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The near-Earth objects and their potential threat to our planet
Abstract
The near-Earth object (NEO) population includes both asteroids (NEAs)
and comet nuclei (NECs) whose orbits have perihelion distances q<1.3
AU and which can approach or cross that of the Earth. A NEA is defined
as a “potentially hazardous asteroid” (PHA) for Earth when
its minimum orbit intersection distance (MOID) comes inside 0.05 AU and
it has an absolute magnitude H<22 mag (i.e. mean diameter > 140
m). These are big enough to cause, in the case of impact with Earth,
destructive effects on a regional scale. Smaller objects can still
produce major damage on a local scale, while the largest NEOs could
endanger the survival of living species. Therefore, several national and
international observational efforts have been started (i) to detect
undiscovered NEOs and especially PHAs, (ii) to determine and
continuously monitor their orbital properties and hence their impact
probability, and (iii) to investigate their physical nature. Further
ongoing activities concern the analysis of possible techniques to
mitigate the risk of a NEO impact, when an object is confirmed to be on
an Earth colliding trajectory. Depending on the timeframe available
before the collision, as well as on the object’s physical
properties, various methods to deflect a NEO have been proposed and are
currently under study from groups of experts on behalf of international
organizations and space agencies. This paper will review our current
understanding of the NEO population, the scientific aspects and the
ongoing space- and ground-based activities to foresee close encounters
and to mitigate the effects of possible impacts.
... From the ground, the near Sun regions are only observable for a small fraction of the night. Several search programs (Stokes et al., 2002;Perna et al., 2013;Vereš et al., 2009) have been undertaken to map the entire population of NEOs, among them the Spaceguard Survey catalogued 90% of NEOs with diameter larger than 1 km. ...
... However, if a Tunguska-class or smaller NEO approaches the Earth from the Sun direction, its observation from ground is very difficult or even impossible, this was the case of the meteorite fall in Chelyabinsk, Russia, in February 2013 (Zuluaga and Ferrin, 2013 et al., 2014). Because the sky region next to the Sun direction is difficult to observe, space-based systems can integrate ground-based observation for monitoring NEOs from a location in between the Sun and the Earth (Stokes, 2003;Perna et al., 2013). Space-based systems can access a larger portion of the sky with respect to ground-based systems and background noise is reduced due to the lack of atmosphere. ...
... If we assume a limiting visual magnitude V lim below which asteroids can be detected, the limiting absolute magnitude H lim at each time can be obtained from Eq. (7). As the asteroid moves around the Sun, the smallest asteroid size D min that can be detected from a given orbit (i.e., the orbit of the Earth for ground-based survey or the spacecraft's orbit for space-based survey) as a function of time can be obtained as in (Sanchez and Colombo, 2013;Michelsen, 2004;Perna et al., 2013;Werner et al., 2002), ...
We analyse a concept for the detection of Potentially Hazardous Asteroids (PHAs) from a space-based network of telescopes on retrograde distant periodic orbits. Planar periodic orbits are designed in the Sun-Earth circular restricted three-body problem, starting from initial conditions in the Hill’s problem available from the literature. A family of retrograde orbits centred at the Earth is selected as baseline, based on their maximum distance from Earth, larger than the Earth-L2 distance. Indeed, spacecraft on such orbits can detect PHAs incoming from the Sun direction, which could not otherwise be monitored from current Earth-based systems. A trade-off on the orbit amplitude, asteroid diameter to be detected, and the constellation size is performed considering current visible sensor telescope technology. The Chelyabinsk meteor scenario is studied and the potential warning time that could be gained with a space-based survey system with respect to an Earth based-survey system is shown.
... Indeed, some potentially hazardous objects among the NEOs have already altered the evolutionary course of the life on the Earth (Jablonski 1994;Chaloner 2009). Moreover, Perna et al. (2013) suggested that some NEOs possibly will hit our planet at irregular and unpredictable intervals in the future. ...
... The results of NASA's NEOWISE project indicate that there are roughly 4700 ± 1500 PHAs in total, with diameters larger than 140 meters (about 390 feet). 3 In the event of a collision with our planet, PHAs are large enough to pass Earth's atmosphere safely, producing regional or global damage that may even put the very existence of our civilization at risk (Perna et al. 2013). PHAs zing through our planet's vicinity almost every day. ...
Planetary research on the Near-Earth objects (NEOs) has always been a relevant and meaningful topic. Investigating the dynamical behaviour and physical properties of NEOs is significant for understanding the evolution and origin of the solar system. On the other hand, the study of some of these NEOs is crucial for Earth inhabitants because they experience sufficiently close approaches to our planet and are large enough to cause significant damage in the event of an impact. Potentially hazardous asteroids (PHAs) are those having a minimum orbital intersection distance (MOID) with Earth of less than 0.05 AU and an absolute magnitude of 22 or brighter; some of them could impact the Earth within the next century, causing damage on a regional or larger scale. About 1900 PHAs are currently known, of them only 20 to 30 percent have been found, from estimated amounts to \(4700\pm 1500\). They have orbits which could bring them to collide with our planet except those excluded by protective resonance. Because mean motion resonances can protect the planet-crossing objects from disruptive close encounters or collision with the planets, they provide us a practical approach to assess and mitigate the risk of some PHAs. We introduce a numerical technique STD criterion to seek the PHAs in resonance conveniently. A systematic survey of all the discovered PHAs in mean motion resonance with Earth is presented. The resonant configurations of some PHAs in different orders are depicted to illustrate our results further. We identified 176 PHAs (about 9.3% of discovered PHAs) trapped in resonances with Earth, 70 PHAs among them are currently in resonances while others will be captured into particular resonant configurations. Theoretically, the risk of these 176 PHAs is lower and can be neglected for the 22 PHAs in the long-term stable resonant state. We provide a new approach to assess the risk of PHAs. Our conclusions may provide a significant reference for the space missions devoted to PHAs. We indicate some PHAs in co-orbit resonance with Earth and resonances characterized by asymmetric libration. Our findings also highlight some essential properties of resonant dynamics and provide a number of real examples for the research on resonant configurations and resonance capture.
... Fortunately, the collision with the Earth itself is also unlikely. The estimated collision rate is one event roughly every 2000 yrs [5,6]. The probability of impact just after the discovery of a hazardous object is two to three orders * E-mail: tanast@nxt.ru of magnitude lower still. 1 In general, such a body will pass near the Earth several times (and thus be discovered) before it finally collides with the Earth [7,8]. ...
... Let E be the energy of the explosion, E 0 = pE the portion of this energy that is transformed into the kinetic energy of all the fragments (solid, liquid, and gas), with 0 < p < 1, and M = π D 3 /6 the mass of the asteroid. The kinetic energy of the collection of fragments E 0 is equal to half their total mass times the square of the mean speedv, so that In our computations, we used a random-number generator corresponding to the distributions (5), (6). As is known [14,Section 1.2], [15,Section 3.2], this requires the inversion of the function (6), which is strictly growing in the interval [0, 1]; we must find the single root of the following fourth-order equation in this interval: ...
One means of countering a hazardous asteroid is discussed: destruction of the object using a nuclear charge. Explosion of such an asteroid shortly before its predicted collision would have catastrophic consequences, with numerous highly radioactive fragments falling onto the Earth. The possibility of exploding the asteroid several years before its impact is also considered. Such an approach is made feasible because the vast majority of hazardous objects pass by the Earth several times before colliding with it. Computations show that, in the 10 years following the explosion, only a negligible number of fragments fall onto the Earth, whose radioactivity has substantially reduced during this time. In most cases, none of these fragments collides with the Earth. Thus, this proposed method for eliminating a threat from space is reasonable in at least two cases: when it is not possible to undergo a soft removal of the object from the collisional path, and to destroy objects that are continually returning to near-Earth space and require multiple removals from hazardous orbits.
... In the 21st century, humanity faces a number of existential threats in addition to pandemic viruses, ranging from runaway climate change (13) to rising global demand for food (14) and ever-looming concerns about asteroids and volcanism (just ask the dinosaurs) (15). Belligerent governments are once again taking the world to the brink of nuclear war (16). ...
Science currently faces major external and internal threats. External threats include persistent anti-science attacks, the post-pandemic politicization of public health, and chronic underfunding. Internal threats include a proliferation of low-quality studies, an epidemic of retractions, and questions regarding the reproducibility of important research findings. These threats occur just as humanity faces an unprecedented onslaught of existential challenges including climate change, a failing green revolution, pandemics, and severe environmental degradation of the planet, each of which will require scientific solutions. History shows that science is fragile and vulnerable to theocratic, ideological, and authoritarian forces. In this moment of crisis, it is important for all scientists to become foot soldiers in the defense of science.
... Notably, NEOs are also a threat to humanity due to potential collision hazard (e.g. Perna, Barucci & Fulchignoni 2013 ;Perna et al. 2016 ). In particular, NEOs with minimum orbital intersection distance MOID < 0.05 au and absolute magnitude H < 22 are classified as potentially hazardous asteroids (PHAs). ...
... Near-Earth object (NEO) refers to a small celestial body whose orbit perihelion distance is smaller than 1.3 AU [1,2]. If a NEO's minimum orbit intersection distance is inside 0.05 AU and its diameter exceeds 140 m, it will be detected as a potentially hazardous asteroid (PHA) [3]. Besides the monitored PHAs, those asteroids with sizes smaller than 140 m are more dangerous to the Earth. ...
Meteoroid disintegration in the atmosphere can produce airbursts that pose regional/global threats to the Earth. Precise dynamical simulation of hypersonic meteoroids is necessary for human safety. An analysis model that includes spatial structures and non-uniform ablation is needed to understand the evolution of meteoroids and provide inference for the deviation of fragments. This paper proposes a new meteoroid entry method to simulate their trajectory, attitude, ablation, fragmentation, and detonation. N-body configurations of deformable polyhedral granules that can alter the structures of heterogeneous meteoroids are introduced. By manipulating the polyhedron vertices, the rugged surfaces of the meteoroid and the volume change under ablation are described quantitatively. The pressure of the concentrated detonation products is modeled using the Jones-Wilkins-Lee equation of state. To verify the effectiveness of the new method, the expansion of the concentrated detonation products is numerically simulated for the Chelyabinsk meteoroid. Different detonation cases are obtained and presented to demonstrate the laterally/vertically-ejected fragments. Characteristics of both the fragments’ trajectories and the remained terminal masses satisfy the observed results well.
... Таблица 3: Физические параметры исследованных АСЗ и оценки величин A 2 Здесь N -число доступных наблюдений в базе данных MPC. диаметра D и абсолютные звездные величины H астероидов 2005 XY7 и 2007 UM12 даны в таблице 3. Диаметр оценивался по следующей формулеPerna, Barucci и Fulchignoni, 2013: ...
We present the results of astrometric observations of two near-Earth asteroids (2005 XY7 and 2007 UM12) performed in September-November 2023 with the 40-cm Pulkovo telescope in the Assy-Turgen observatory. Stellar and asteroid pixel coordinates were calculated by varying the photo center position, background, and flux values for the PSF (point spread function) based on the analysis of the stellar images. The stars within the 4-arcmin asteroid-centered ring were not involved in the astrometric calibration. These stars were used for the asteroid systematic correction calculation. As a result, the internal accuracy of asteroid positions was better than 0.1 arcsec. The estimation of the mean position and the apparent rate components were performed for each set of CCD frames. Finally, the typical accuracy of the coordinates reached values of 0.024 – 0.088 arcsec. In addition, the numerical integration of the asteroid motion was made by varying the components of the state vector and A2-parameter (Yarkovsky acceleration). The unexpected and statistically insignificant A2 value for the 2007 UM12 has been found. It can be explained by the low quality of the data related to the first approach of this asteroid to the Earth and/or the tidal effects that changed the rotational state of the asteroid. The value A2 = (8.1 ± 6.4) · 10−14 a.u. per day2 on the significance boundary has been calculated for 2005 XY7 asteroid. This value does not contradict well-known data for the same size asteroids.
... Unlike HEDs and ordinary chondrites, which have well-defined absorption features in the Vis-NIR, carbonaceous chondrites lack these diagnostic spectral features and are more difficult to link to their parent bodies. We expect that our grain size study of carbonaceous chondrites will aid in the classification of C-type NEAs that make up ∼20% of the near-Earth object population (Perna et al. 2013). Our results may also aid in the interpretation of Bennu and Ryuguʼs rougher surfaces, which are frequently linked to carbonaceous chondrite meteorites (Clark et al. 2011;Hamilton et al. 2019;Yada et al. 2021;Greenwood et al. 2023). ...
Carbonaceous chondrites are among the most important meteorite types and have played a vital role in deciphering the origin and evolution of our solar system. They have been linked to low-albedo C-type asteroids, but due to subdued absorption bands, definitive asteroid-meteorite linkages remain elusive. A majority of these existing linkages rely on fine-grained (typically < 45 μm) powders across a limited wavelength range in the visible to near-infrared (0.35-2.5 μm). While this is useful in interpreting the fine-grained regolith of larger main-belt objects like Ceres, recent spacecraft missions to smaller near-Earth asteroids (NEAs), such as Bennu and Ryugu, have shown that their surfaces are dominated by larger grain size material. To better interpret the surfaces of these smaller, carbonaceous NEAs, we obtained laboratory reflectance spectra of seven carbonaceous chondrite meteorite groups (CI, CM, CO, CV, CR, CK, C2-ungrouped) over the ultraviolet to mid-infrared range (0.2-14 μm). Each meteorite contained five grain size bins (45-1000 μm) to help constrain spectral grain size effects. We find a correlation between grain size and absolute reflectance, spectral slope, band depth, and the Christiansen feature band center. Principal component analysis of grain size variation illustrates a similar trend to lunar-style space weathering. We also show that the Bus-DeMeo asteroid taxonomic classification of our samples is affected by grain size, specifically shifting CM2 Aguas Zarcas from a Ch-type to B-type with increasing grain size. This has implications for the parent body of the OSIRIS-REx target, Bennu. With Aguas Zarcas, we present results from Hapke modeling.
... on civilization (Perna, Barucci & Fulchignoni 2013 ). The planetary defence missions to de vise ef ficient mitigation strategies critically depend on timely detection and accurate knowledge of orbits and physical properties of these potentially hazardous asteroids (Nakano et al. 2022 ;Reddy 2022 ). ...
The detection and accurate astrometry of fast-moving near-Earth objects (NEOs) has been a challenge for the follow-up community. Their fast apparent motion results in streaks in sidereal images, thus affecting the telescope’s limiting magnitude and astrometric accuracy. A widely adopted technique to mitigate trailing losses is non-sidereal tracking, which transfers the streaking to background reference stars. However, no existing publicly available astrometry software is configured to detect such elongated stars. We present Astreaks, a streaking source detection algorithm, to obtain accurate astrometry of NEOs in non-sidereal data. We validate the astrometric accuracy of Astreaks on 371 non-sidereally tracked images for 115 NEOs with two instrument set-ups of the GROWTH-India Telescope. The observed NEOs had V-band magnitude in the range [15, 22] with proper motion up to 140″/min, thus resulting in stellar streaks as high as 6.5′ (582 pixels) in our data. Our method obtained astrometric solutions for all images with 100% success rate. The standard deviation in Observed-minus-Computed (O-C) residuals is 0.52″, with O-C residuals <2″ (<1″) for 98.4% (84.4%) of our measurements. These are appreciable, given the pixel scale of ∼0.3″ and ∼0.7″ of our two instrument set-ups. This demonstrates that our modular and fully-automated algorithm helps improve the telescope system’s limiting magnitude without compromising astrometric accuracy by enabling non-sidereal tracking on the target. This will help the NEO follow-up community cope with the accelerated discovery rates and improved sensitivity of the next-generation NEO surveys. Astreaks has been made available to the community under an open-source license.
... In case of possible impactors, their physical characterization is crucial to defining successful mitigation strategies [6]. Unfortunately, more than 85% of the ~18.000 known NEOs still lack a compositional characterization, and their increasing discovery rate (currently 1.900 objects year) makes the situation progressively worse. ...
... Asteroid science encompasses studies ranging from formation mechanisms, population, collisional evolution, orbital dynamics, compositional properties and physical mechanisms such as Yarkovsky and YORP effects (Michel et al. 2015). Out of all small solar system bodies, NEOs are of particular interest to the planetary science community, not only from a scientific perspective but also because of the hazardous consequences of their impacts on civilization (Perna et al. 2013). The planetary defence missions ★ E-mail: kritti@caltech.edu ...
The detection and accurate astrometry of fast-moving near-Earth objects (NEOs) has been a challenge for the follow-up community. Their fast apparent motion results in streaks in sidereal images, thus affecting the telescope's limiting magnitude and astrometric accuracy. A widely adopted technique to mitigate trailing losses is non-sidereal tracking, which transfers the streaking to background reference stars. However, no existing publicly available astrometry software is configured to detect such elongated stars. We present Astreaks, a streaking source detection algorithm, to obtain accurate astrometry of NEOs in non-sidereal data. We validate the astrometric accuracy of Astreaks on 371 non-sidereally tracked images for 115 NEOs with two instrument set-ups of the GROWTH-India Telescope. The observed NEOs had V-band magnitude in the range [15, 22] with proper motion up to 140$^{\prime\prime}$/min, thus resulting in stellar streaks as high as 6.5$^\prime$ (582 pixels) in our data. Our method obtained astrometric solutions for all images with 100% success rate. The standard deviation in Observed-minus-Computed (O-C) residuals is 0.52$^{\prime\prime}$, with O-C residuals <2$^{\prime\prime}$(<1$^{\prime\prime}$) for 98.4% (84.4%) of our measurements. These are appreciable, given the pixel scale of $\sim$0.3$^{\prime\prime}$ and $\sim$0.7$^{\prime\prime}$ of our two instrument set-ups. This demonstrates that our modular and fully-automated algorithm helps improve the telescope system's limiting magnitude without compromising astrometric accuracy by enabling non-sidereal tracking on the target. This will help the NEO follow-up community cope with the accelerated discovery rates and improved sensitivity of the next-generation NEO surveys. Astreaks has been made available to the community under an open-source license.
... Notably, NEOs are also a threat to humanity due to potential collision hazard (e.g. Perna, Barucci & Fulchignoni 2013 ;Perna et al. 2016 ). In particular, NEOs with minimum orbital intersection distance MOID < 0.05 au and absolute magnitude H < 22 are classified as potentially hazardous asteroids (PHAs). ...
We present new results of the observing program which is a part of the NEOROCKS project aimed to improve knowledge on physical properties of near-Earth Objects (NEOs) for planetary defense. Photometric observations were performed using the 1.2m telescope at the Haute-Provence observatory (France) in the BVRI filters of the Johnson-Cousins photometric systems between June 2021 and April 2022. We obtained new surface colors for 42 NEOs. Based on the measured colors we classified 20 objects as S-complex, 9 as C-complex, 9 as X-complex, 2 as D-type, one object as V-type, and one object remained unclassified. For all the observed objects we estimated their absolute magnitudes and diameters. Combining these new observations with the previously acquired data within the NEOROCKS project extended our dataset to 93 objects. The majority of objects in the dataset with diameters D<500m belongs to a group of silicate bodies, which could be related to observational bias. Based on MOID and ΔV values we selected 14 objects that could be accessible by a spacecraft. Notably, we find D-type asteroid (163014) 2001 UA5 and A-type asteroid 2017 SE19 to be of particular interest as possible space mission targets.
... Investigation of NEOs provides us with an opportunity to better understand the evolution of the solar system and the processes that took place at the early stages of its formation. Notably, NEOs are also a threat to humanity due to potential collision hazard (e.g., Perna et al. 2013Perna et al. , 2016. In particular, NEOs with minimum orbital intersection distance MOID<0.05 ...
We present new results of the observing program which is a part of the NEOROCKS project aimed to improve knowledge on physical properties of near-Earth Objects (NEOs) for planetary defense. Photometric observations were performed using the 1.2m telescope at the Haute-Provence observatory (France) in the BVRI filters of the Johnson-Cousins photometric systems between June 2021 and April 2022. We obtained new surface colors for 42 NEOs. Based on the measured colors we classified 20 objects as S-complex, 9 as C-complex, 9 as X-complex, 2 as D-type, one object as V-type, and one object remained unclassified. For all the observed objects we estimated their absolute magnitudes and diameters. Combining these new observations with the previously acquired data within the NEOROCKS project extended our dataset to 93 objects. The majority of objects in the dataset with diameters D<500m belongs to a group of silicate bodies, which could be related to observational bias. Based on MOID and $\Delta$V values we selected 14 objects that could be accessible by a spacecraft. Notably, we find D-type asteroid (163014) 2001 UA5 and A-type asteroid 2017 SE19 to be of particular interest as possible space mission targets.
... Identifying the distribution of OH/H 2 O within the NEA population will constrain the OH/H 2 O budget of the inner solar system, as well as aid in general compositional understanding of this varied population. Such a study aids in not only understanding solar system formation but also hazard mitigation for spacecraft and planetary defense (e.g., Lee 1996;Britt et al. 2002;Opeil et al. 2012;Perna et al. 2013), as well as asteroid resource utilization (e.g., Lewis & Huston 1993;Nichols 1993;Sanchez & McInnes 2012). ...
Near-Earth Asteroids (NEAs) are excellent laboratories for processes that affect airless body surfaces. S-complex (including V-type) NEAs were not expected to contain OH/H 2 O on their surfaces because they formed in the anhydrous regions of the solar system and their surface temperatures are high enough to remove these volatiles. However, a 3 μ m feature typically indicative of OH/H 2 O was identified on other seemingly dry bodies in the inner solar system, raising the question of how widespread volatiles may be on NEAs. We observed 29 NEAs using both prism (0.7–2.52 μ m) and LXD_short (1.67–4.2 μ m) modes on SpeX on NASA’s IRTF in order to accurately characterize asteroid spectral type and the 3 μ m region. Eight of the observed NEAs have a 3 μ m absorption feature at >1 σ (three of which are present to >2 σ ), and they exhibit four identified band shape types. Possible sources for OH/H 2 O on these bodies include carbonaceous chondrite impacts and/or interactions with protons implanted by solar wind. Characteristics such as composition and aphelion appear to play an important role in the delivery and/or retention of OH/H 2 O, as all eight NEAs with an absorption feature are S-complex asteroids and six enter the main asteroid belt. Additionally, perihelion, size, albedo, and orbital period may play a minor role. Our observations determined that nominally anhydrous, inner solar system bodies, and therefore near-Earth space in general, contain more OH/H 2 O than previously expected. The identified trends should help predict which NEAs that have not yet been observed might contain OH/H 2 O on their surfaces.
... NEOs are usually only observable during their close approach to Earth, meaning that they can be lost if their ephemeris has a large uncertainty due to observations with low precision or only from a small orbital arc (Micheli et al., 2014). Additionally, perturbation by gravitational forces of other objects or non-gravitational forces like absorption and emission of radiation are increasing the uncertainty (Bottke et al., 2006;Perna et al., 2013). The targeted recovery of such lost object is so difficult, such that it rather will be found again by ordinary survey observations (Milani, 1999). ...
The observation of small bodies in the Space Environment is an ongoing important task in astronomy. While nowadays new objects are mostly detected in larger sky surveys, several follow-up observations are usually needed for each object to improve the accuracy of orbit determination. In particular objects orbiting close to Earth, so called Near-Earth Objects are of special concern as a small but not negligible fraction of them can have a non-zero impact probability with Earth. Telescopes are often hosted by amateur observatories. With upcoming new NEO search campaigns by very wide field of view telescopes, like the Vera C. Rubin Observatory, NASA's NEO surveyor space mission and ESA's Flyeye telescopes, the number of NEO discoveries will increase dramatically. This will require an increasing number of useful telescopes for follow-up observations at different geographical locations. While well-equipped amateur astronomers often host instruments which might be capable of creating useful measurements, both observation planning and scheduling, and also analysis are still a major challenge for many observers. In this work we present a fully robotic planning, scheduling and observation pipeline that extends the widely used open-source cross-platform software KStars/Ekos for INDI devices. The method consists of algorithms which automatically select NEO candidates with priority according to ESA's NEOCC. It then analyses detectable objects (based on limiting magnitudes, geographical position, and time) with preliminary ephemeris from the Minor Planet Center. Optimal observing slots during the night are calculated and scheduled. Immediately before the measurement the accurate position of the minor body is recalculated and finally the images are taken. Besides the detailed description of all components, we will show a complete robotic hard- and software solution based on our methods.
... This interplay controls the properties of the asteroid's interior and shape, which, with their surface properties and composition, 25 influences any attempt to deflect an asteroid in a planetary defense scenario to protect Earth (Tanbakouei et al. 2019). Therefore, assessing the geology of an NEA provides clues to how it has evolved, what its internal structure may look like, and how it might respond to any attempted deflection (e.g., Gehrels 1994;Perna et al. 2013). In particular, knowledge of the geological nature of Dimorphos' surface, i.e., whether it is smooth or boulder rich (Durda et al. 2011;Guettler et al. 2012;Tatsumi & Sugita 2018;Walsh et al. 2019;Jawin et al. 2022), whether its surface has steep slopes , or whether the surface shows signs of being unusually weak or strong (Arakawa et al. 2020;Lauretta et al. 2022;Barnouin et al. 2022;Walsh et al. 2022) is especially critical for the DART impactor to understand how momentum is transferred, hence influencing the efficacy of deflection (Cheng et al. 2018). ...
On 2022 September 26, the DART spacecraft will impact the surface of Dimorphos, the ∼160 m size satellite of the binary near-Earth asteroid (NEA) (65803) Didymos. What will be observed on the surfaces of both asteroids and at the DART impact site is largely unknown, beyond the details of Didymos revealed by previous Arecibo and Goldstone radar observations. We present here the expected DART and LICIACube observations of the Didymos system and discuss the planned mapping strategies. By searching similar geological features and processes identified on other NEAs, we constrain the impact conditions that DART might encounter at Dimorphos, assessing both the asteroid’s surface and interior structure.
... The mission will autonomously navigate to and intentionally collide with a target asteroid, thereby demonstrating the kinetic impactor technique for deflecting an asteroid (Cheng et al. 2020;Rivkin et al. 2021). The kinetic impactor technique is one of several approaches for deflecting a potentially hazardous asteroid off a collision course with Earth (e.g., Gehrels et al. 1994;Perna et al. 2013). ...
The Double Asteroid Redirection Test (DART) is the first planetary defense test mission. It will demonstrate the kinetic impactor technique by intentionally colliding the DART spacecraft with the near-Earth asteroid Dimorphos. The main DART spacecraft is accompanied by the Italian Space Agency Light Italian CubeSat for Imaging of Asteroids (LICIACube). Shape modeling efforts will estimate the volume of Dimorphos and constrain the nature of the impact site. The DART mission uses stereophotoclinometry (SPC) as its primary shape modeling technique. DART is essentially a worst-case scenario for any image-based shape modeling approach because images taken by the camera on board the DART spacecraft, called the Didymos Reconnaissance and Asteroid Camera for Optical navigation (DRACO), possess little stereo and no lighting variation; they simply zoom in on the asteroid. LICIACube images add some stereo, but the images are substantially lower in resolution than the DRACO images. Despite the far-from-optimal imaging conditions, our tests indicate that we can identify the impact site to an accuracy and precision better than 10% the size of the spacecraft core, estimate the volume of Dimorphos to better than 25%, and measure tilts at the impact site over the scale of the spacecraft with an accuracy better than 7°. In short, we will know with excellent accuracy where the DART spacecraft hit, with reasonable knowledge of local tilt, and determine the volume well enough that uncertainties in the density of Dimorphos will be comparable to or dominate the uncertainty in the estimated mass. The tests reported here demonstrate that SPC is a robust technique for shape modeling, even with suboptimal images.
... [retrieved July 2021]), belong to the class of potential hazardous near-Earth asteroids (PHAs) [1][2][3][4][5][6][7]. These PHAs frequently make close approaches to Earth's orbit, and therefore, the hazard caused by PHAs is still a very real and ever-present threat [8,9]. Two well-known events are the Tunguska event in 1908 [10] and the Chelyabinsk meteor event in 2013 [11,12], in which a 17 m asteroid entered Earth's atmosphere, damaged thousands of buildings and injured more than 1500 residents. ...
The threat of potential hazardous near-Earth asteroid (PHA) impact on Earth is increasingly attracting public attention. Monitoring and early warning of those PHAs are the premise of planetary defense. In this paper, we proposed a novel concept of surveillance constellation of heterogeneous wide-field near-Earth asteroid (NEA) surveyors (CROWN), in which six space-based surveyors are loosely deployed in Venus-like orbits to detect the NEAs along the direction of the sunlight. First, the concept and overall design of the NEA surveillance constellation are discussed. Second, the transfer and deployment trajectory of the surveyors are investigated based on the Sun-Venus three-body system. The Sun-Venus libration orbit is taken as the parking orbit, and its stable invariant manifolds are used to reduce the deployment fuel consumption. Next, the detection performance of the CROWN was evaluated considering constraints of apparent visual magnitude and field of view. The NEA orbit determination (OD) using the CROWN was studied and verified. Simulation results show that the CROWN can be deployed with a total velocity increment of approximately 300 m/s. During the 5 years of observation, 99.8% of PHAs can be detected and the OD precision is better than a single-surveyor system. This paper can provide a reference for the construction of future asteroid defense system.
... Besides being objects of great scientific interest, Near-Earth Asteroids (NEAs) also represent a potential threat to human life and civilization (for a review of such topics, see e.g. Perna et al., 2013). ...
“LICIACube – the Light Italian Cubesat for Imaging of Asteroids” is managed by the Italian Space Agency (ASI) and will be part of the NASA DART mission, with the aim of i) documenting the DART impact’s effects on the secondary member of the (65803) Didymos binary asteroid system, ii) characterizing the shape of the target, and iii) performing dedicated scientific investigations on it. DART probe will be launched in mid 2021 and LICIACube will be hosted as piggyback during the 15 months of interplanetary cruise, then released 10 days before the impact, and autonomously guided along its fly-by trajectory. The LICIACube payload is composed by LEIA, a narrow FoV camera, and LUKE, a wide FoV imager with an RGB Bayer pattern filter, that will collect and transmit to Earth several unique images of the effects of the DART impact on the asteroid, such as the formation and the development of the plume potentially determined by the impact.
LICIACube will be the first deep space mission developed and autonomously managed by an Italian team: the design, integration and test of the CubeSat have been assigned by ASI to the aerospace company Argotec, while the LICIACube Ground Segment has a complex architecture based on the Argotec Mission Control Centre, antennas of the NASA Deep Space Network and data archiving and processing, managed at the ASI Space Science Data Center. The LICIACube team includes a wide Italian scientific community, involved in the definition of all the aspects of the mission: trajectory design; mission definition (and real-time orbit determination during operations); impact, plume and imaging simulation and modelling, in preparation of a suitable framework for the analysis and interpretation of in-situ data. The major technological mission challenge, i.e. the autonomous targeting and imaging of such a small body during a fast fly-by, to be accomplished with the limited resources of a CubeSat, is affordable thanks to a strong synergy of all the mentioned teams in support of the engineering tasks.
... The analysis of Near Earth Asteroids is of high importance partly because these objects are easily accessible for spacecraft (Michel et al., 2014), and samples could be returned on moderate cost (Duffard et al., 2011;Fujiwara et al., 2000;Lauretta et al., 2017). The other main reason for their analysis is the preparation for asteroid deflection to avoid a possible impact (Chapman, 1994;Cheng et al., 2016;Losiak et al., 2017;Perna et al., 2013). This paper focuses on the mid-infrared observational possibilities to prepare thermal infrared observations for the HERA (formerly named AIM, Michel et al., 2016Michel et al., , 2018 mission of ESA that targets the Didymos double asteroid, also the target of the NASA DART impacting mission (Cheng et al., 2017;Stickle et al., 2016). ...
Near future missions to Near Earth Asteroids could provide new information exploiting the middle-infrared (2.5–25 μm) region, as at the temperature range of asteroids at Earth’ solar distance the maximal energy is emitted in this region. The IR range is ideal for the analysis and separation of various silicate types. This work reviews the background knowledge and evaluates the possibilities for mineral identification using high resolution laboratory data. Examples are presented using laboratory based meteorite powder data to evaluate the possibility for identification of plagioclase, estimation on the Mg/(Mg + Fe) ratio and other characteristics. The expected peak position shift from temperature differences on a rotating asteroid might be below 0.01 μm, while the fine structure of bands requires high spectral resolution as well. However, with moderate resolution, the analysis of three main minerals is still possible, focusing at the range of 12.5–9.09 μm (800-1100 cm⁻¹) with spectral resolution of about 0.08 μm (10 cm⁻¹), to identify the expected main bands of olivine, pyroxene and feldspars.
An infrared camera at small orbital distance around the target could resolve fine powder covered areas like dust ponds or separate blocks. For this task an angular resolution below 0.05° might be required. Such observations would provide a wide range of important data both on surface composition, granular processes and space weathering on asteroid surfaces. However, further targeted laboratory analysis is necessary, especially using pure minerals of different grain size and meteorite powder mixtures.
... Asteroid threat is very important problem [1][2][3][4][5]. Up to now many methods to mitigate the asteroidal hazard are proposed. ...
This paper deals with one of the methods asteroid hazard mitigation. The preventive destruction of a hazardous asteroid during the previous close encounter before its predicted collision is considered. Two variants of the explosion are considered: in the first case a projectile overtakes an asteroid; in the second one the situation is contrary. The second way requires significantly lower velocity of spacecraft delivery. On the other hand, it loses to the first way, since the number of fragments falling to the Earth is about an order of magnitude larger. However, with a more careful approach (non-isotropic explosion), this unfavorable factor can be likely reduced.
... The so-called Near Earth Objects (NEOs) are comets and asteroids with perihelion distances < 1.3 AU. The following orbital elements: semi-major axis (a), perihelion distance ( ), and aphelion distance ( ), are used to classify NEOs into the two following categories (Chodas, 2017a;Perna et al., 2013). The first one, consisting of Near-Earth Comets (NECs), is described by values of < 1.3 AU and an orbital period < 200 years. ...
The dynamics of asteroids’ trajectories constitute potential threats to the Earth in the hypothetical case where the orbit of such an object crosses the orbit of the Earth. For this reason, advanced monitoring systems such as NASA JPL Sentry continually scan trajectories of Near-Earth Asteroids (NEAs), in addition to other celestial bodies. A large amount of data concerning NEAs is provided by such systems, including estimations of the impact probabilities as well as predictions of impact dates. In this paper, we apply a novel methodology to rank the impact dates of NEAs based on the data provided by Sentry. This approach carries out a comparison process via a novel Multi-Criteria Decision Making (MCDM) method named the Reference Ideal Method (RIM). It takes into account several NEA features, such as distance to the Earth, width, and impact energy, and establishes comparisons with respect to the impact dates of a population of non-small NEAs with those ones from noteworthy objects 410777 (2009 FD), 29075 (1950 DA), and 101955 Bennu (1999 RQ36). The obtained results have been found to be quite consistent, allowing the authors to present this methodology as a novel metric to assess impact dates of hazardous NEAs.
... Studying and characterizing the small-body population within the neighborhood of Earth is critical to understanding the threat of near-Earth asteroids. Accordingly, several national and international efforts aim to discover and track these objects, as well as to investigate their physical nature [2]. Characterizing the physical composition and orbital behavior of HO 3 may inform how this asteroid population was formed and increase understanding of these threatening objects. ...
The Near-Earth Asteroid Characterization and Observation (NEACO) mission is a concept study proposing to explore the fast-rotating asteroid (469219) 2016 HO3, one of Earth's few quasi-satellites. In this study, a SmallSat spacecraft performs a scientific investigation that characterizes the asteroid at a sufficient degree to enable future, more in-depth missions. The 166 kg NEACO spacecraft uses a low-thrust, solar electric propulsion system to reach HO3 within 22 months from launch. Its instrument suite consists of two optical cameras, two spectrometers, an altimeter, and a low-velocity impactor. Upon arrival at HO3, NEACO uses pulsed plasma thrusters to hover at varying altitudes to enable lit surface mapping, shape modeling, and surface spectroscopy. The spacecraft will then perform several flybys to estimate the asteroid's mass. Finally, NEACO releases a low-velocity impactor during very low-altitude hovering to validate the existence of regolith and estimate the magnitude of surface cohesion. The science operations are completed within 8 months and the total mission is completed in less than 3 years. The NEACO mission concept integrates novel small-body analyses and proximity operation techniques with high-technology-readiness-level spacecraft components to achieve its science objectives within a reasonable mission timeline.
... Studying and characterizing the small-body population within the neighborhood of Earth is critical to understanding the threat of near-Earth asteroids. Accordingly, several national and international efforts aim to discover and track these objects, as well as to investigate their physical nature [2]. Characterizing the physical composition and orbital behavior of HO 3 may inform how this asteroid population was formed and increase understanding of these threatening objects. ...
The Near-Earth Asteroid Characterization and Observation (NEACO) mission proposes to explore the fast-rotating asteroid (469219) 2016 HO3 with a SmallSat spacecraft and perform an early scientific investigation to enable future, more indepth missions. The NEACO spacecraft is equipped with a low-thrust, solar electric propulsion system to reach its target within two years, making use of an Earth gravity assist. Its instrument suite consists of two optical cameras, a spectrometer, an altimeter, and an explosive impactor assembly. Upon arrival at HO3 , NEACO uses pulsed plasma thrusters to hover, first at a high altitude of 50 km to perform lit surface mapping and shape modeling, and later at a lower altitude of 10 km to refine these models and perform surface spectroscopy. Following the hovering phases, the spacecraft performs several flybys with decreasing periapses in order to estimate the asteroid’s mass. Finally, NEACO uses an additional flyby to release an explosive impactor that craters the asteroid surface. After spending a few weeks at a safe hovering distance, the spacecraft returns and images the crater and freshly exposed sub-surface material. This provides information on the strength of the asteroid surface. The science operations are completed within eight months, with the total mission lasting less than three years. The objectives met by the NEACO mission satisfy all science goals for the student competition of the 2017 AAS Astrodynamics Specialist Conference.
... In recent years, the importance of the problem of asteroid-comet hazards (ACHs) has become generally recognized, and many scientific publications have been devoted to this issue (see, e.g., [1][2][3][4][5][6][7]). Currently, mainly due to the Space Guard Program implemented in the United States, the majority (~90%) of all large, potentially hazardous objects (PHOs) has been revealed. ...
The concept of the System for the Observation of Daytime Asteroids (SODA system) has been developed, the purpose of which is to detect at least 95% of hazardous celestial bodies larger than 10 m in size that fly towards Earth from the Sun side. Spacecraft, equipped with the optimum version, which has three wide-angle optical telescopes of small aperture (20–30 cm) will be placed in a halo orbit around the L1 libration point of the Sun–Earth system. This will provide a warning on the hazardous object, approaching from the Sun side, and will allow one to determine the orbit and the point of body entering Earth atmosphere to a sufficient accuracy, at least a few hours before the body collides with Earth. The requirements to the system are considered, the results of a preliminary design of the set of instruments have been described, the areas of visibility are calculated, and the versions of data transmission modes have been proposed. It has been shown that, in cooperation with other (particularly ground-based) projects aimed to observing objects flying from the night sky side, it is possible to detect in advance all hazardous bodies in the near-Earth space larger than 10 m in size that approach Earth from almost any direction.
... Interpretation of this type of flux data yields important clues about the near-Earth object (NEO) population, helps identify and recover freshly fallen meteorites, and provides valuable insights for projects that are focused on space hazards (Shustov 2010;Perna et al. 2013;Harris et al. 2013;Emel'yanenko and Shustov 2013;Reinhardt et al. 2013). For all these applications it is crucial to evaluate the object's pre-atmospheric size and mass based on such observations in order to build a realistic model of atmospheric entry which takes into account the changes in mass along the trajectory, and to derive an impact scale that reflects the consequences of the collision with the planet and its corresponding level of threat (Collins et al. 2005;Gritsevich et al. 2012;Turchak and Gritsevich 2014;Moreno-Ibáñez et al. 2016). ...
Out of a total around 50,000 meteorites currently known to science, the atmospheric passage was recorded instrumentally in only 25 cases with the potential to derive their atmospheric trajectories and pre-impact heliocentric orbits. Similarly, while observations of meteors generate thousands of new entries per month to existing databases, it is extremely rare they lead to meteorite recovery (http:// www. meteoriteorbits. info/ ). These 25 exceptional cases thus deserve a thorough re-examination by different techniques—not only to ensure that we are able to match the model with the observations, but also to enable the best possible interpretation scenario and facilitate the robust extraction of key characteristics of a meteoroid based on the available data. In this study, we evaluate the dynamic mass of the Košice meteoroid using analysis of drag and mass-loss rate available from the observations. We estimate the dynamic pre-atmospheric meteoroid mass at 1850 kg. The pre-fragmentation size proportions of the Košice meteoroid are estimated based on the statistical distribution of the recovered meteorite fragments. The heliocentric orbit of the Košice meteoroid, derived using numerical integration of the equations of motion, is found to be in close agreement to earlier published results.
... Interpretation of this type of flux data yields important clues about the near-Earth object (NEO) population, helps identify and recover freshly fallen meteorites, and provides valuable insights for projects that are focused on space hazards (Shustov 2010;Perna et al. 2013;Harris et al. 2013;Emel'yanenko and Shustov 2013;Reinhardt et al. 2013). For all these applications it is crucial to evaluate the object's pre-atmospheric size and mass based on such observations in order to build a realistic model of atmospheric entry which takes into account the changes in mass along the trajectory, and to derive an impact scale that reflects the consequences of the collision with the planet and its corresponding level of threat Turchak and Gritsevich 2014;. ...
This volume is a compilation of the research presented at the International Asteroid Day workshop which was celebrated at Barcelona on June 30th, 2015. The proceedings discuss the beginning of a new era in the study and exploration of the solar system’s minor bodies. International Asteroid Day commemorates the Tunguska event of June 30th, 1908. The workshop’s goal was to promote the importance of dealing proactively with impact hazards from space. Multidisciplinary experts contributed to this discussion by describing the nature of comets and asteroids along with their offspring, meteoroids. New missions to return material samples of asteroids back to Earth such as Osiris-REx and Hayabusa 2, as well as projects like AIM and DART which will test impact deflection techniques for Potentially Hazardous Asteroids encounters were also covered.
The proceedings include both an outreach level to popularize impact hazards and a scientific character which covers the latest knowledge on these topics, as well as offering proposals of promising new techniques that will help gain new insights of the properties of these challenging bodies by studying meteoroids and meteorites. Asteroids, comets, meteoroids and meteorites are introduced with descriptions of their nature, origin, and solar system pathways.
The effect of the destruction of asteroids in orbits as they approach the Earth, and the consequences of their impacts, have been estimated. The areas affected by a shock wave, a seismic wave, and radiation upon impact of stony asteroids on land or upon entry into the atmosphere over land at a speed of 20 km/s are determined for a range of their sizes of 20–500 m. It has been found that arbitrary destruction of an asteroid near the Earth can lead to an increase in the total area affected by shock waves and thermal radiation during impacts of individual fragments. In the general case, reduction of damage after the destruction of asteroids with diameters of 150–500 m can be achieved if the bulk of the fragments are bodies with dimensions of less than 20–30 m, which do not pose a catastrophic danger.
La Tierra, nuestro hogar en el cosmos, enfrenta una amenaza latente que podría cambiar el rumbo de la humidad. ¿Qué pasaría si un colosal asteroide se dirigiera hacia nuestro planeta? ¿Tenemos la capacidad de afrontar ese desafío? En este apasionante viaje literario, especialistas en astrofísica, filosofía, derecho, psicología, comunicación y ecología se unen para explicar el fascinante mundo de la defensa planetaria. Descubrirás cómo disantos campos del conocimiento convergen para brindarnos una visión integral sobre el peligro de impacto de objetos celestes y sus analogías con otros riesgos globales. Tanto personas curiosas como investigadoras profesionales disfrutarán del ejercicio de creatividad y rigurosidad que supone esta obra colaborativa. Una invitación a la reflexión y al compromiso para salvaguardar nuestro lugar en el universo y asegurar un futuro a las generaciones venideras.
In recent decades, growing interest has arisen within the scientific community in asteroids, in particular near-Earth objects (NEOs), which are asteroids or comets characterized by a semimajor axis close to that of the Earth. Interest in these objects is motivated not only by their capability of providing answers to important questions concerning the origins of the solar system, but also by the threat of a possible future collision with Earth. It is quite common for NEOs to have peculiar orbits, with non-negligible inclinations and/or eccentricities. This implies that a rendezvous mission with such objects requires a large propellant consumption and gravity-assist maneuvers that significantly increase flight time when chemical (and also electrical) thrusters are used. Therefore, a promising option for exploring NEOs is provided by a propellantless propulsive system as solar sails or electric solar wind sails (E-sails), which are capable of generating thrust without consuming any propellant. In this chapter, the optimal solar sail- or E-sail-based transfers towards some of the most relevant NEOs are generated by solving an optimal control problem through an indirect approach. The results are compared with the transfer times obtained assuming a chemical thruster and a bi-impulsive maneuver.
Potentially hazardous asteroids (PHAs) are objects which can have close encounters with Earth and are significantly large to cause significant regional damage in the event of impact. The mitigation strategy requires to understand their physical properties. We aim to investigate the physical nature of PHAs, using data obtained within the framework of the Visible NEOs Observations Survey (ViNOS). We analyzed and characterized a sample comprised of 14 of these objects. To conduct this study, we obtained visible spectra of 14 PHAs in the 0.5–0.9μm region using the 2.5m Nordic Optical Telescope, located at the El Roque De Los Muchachos Observatory in La Palma (Spain). The resulting spectra were combined with their corresponding near-infrared counterparts, available in the literature from the Small Main-Belt Asteroid Spectroscopic Survey (SMASS). We performed a taxonomical classification, computed several diagnostic spectral parameters (slopes, band centres, and band area ratios), and provide completely new mineralogical information for 10 of these objects. We also compared the data with laboratory spectra of meteorites from the RELAB database. Among the studied sample of PHAs, approximately 90 per cent of the objects (13 out of 14) were classified as silicaceous (S-types and subclasses). Only one object, 489486, was classified as carbonaceous. Five of the studied PHAs did not have previous taxonomic classifications. The comparisons of the silicaceous PHAs with meteoritic spectra yielded, in all cases, ordinary chondrites (OCs) as the best match for meteoritic analogs. The computed mineralogy of all of our targets is also consistent with this results.
Rotations of asteroids have been set and altered by several processes since their formation. In the case of the near-Earth objects (NEOs), the rotational states are significantly affected by non-gravitational effects. In addition, an abundant population of binary systems has been found among NEOs with rotational periods very close to the spin barrier and in the size range from 0.2 to 10 km. In this paper we report photometric observations of about 80 NEAs carried out with the 1-m telescope of the Observatório Astronômico do Sertão de Itaparica (OASI, Brazil) from 2016 October to 2020 December. Reliable rotational periods and lightcurve amplitudes were determined for 46 objects, of which 15 are Potentially Hazardous Asteroids (PHAs). A minimum period value was also derived for other 11 NEOs. Then, asteroids with rotation periods between 2 and 3 h had their lightcurves analyzed for binarity signatures. We analyzed 21 binary candidates and for 8 of them we found the signature of a possible satellite. These suspected binaries showed a single possible mutual event or a secondary period superimposed on the lightcurve. Primary lightcurves for 6 confirmed binary NEOs were also obtained and for some of them the orbital period was also determined. Finally, we show that binary candidates require some internal cohesion strength to avoid structural failure by centrifugal forces.
The aim of this work is to investigate the performance of a solar sail-based spacecraft in an optimal apse line rotation maneuver. Considering a heliocentric two-body motion and a low-performance solar sail with an ideal force model, this study derives the optimal steering law that maximizes the final rotation angle of the osculating orbit apse line. Starting from an approximated (Gaussian) form of the Lagrange’s planetary equations, the achievable argument of periapsis and the required flight times are obtained in a parametric way, for given values of parking orbit eccentricity and sail (reference) propulsive acceleration, as the solutions of an optimal control problem. The numerical simulations show that, for sufficiently large values of the orbit eccentricity, the maximum argument of periapsis is roughly proportional to the sail (reference) propulsive acceleration. An approximate locally-optimal steering law is also derived, and the results of the optimization problem are applied to Earth- and Venus-following orbits, where the planets trajectories are assumed to be circular and coplanar with the spacecraft parking orbit.
Current investigation is devoted to ongoing follow-up observations of fast-moving Near-Earth Asteroids (NEAs) carried out with Rotating-drift-scan CCD technique on small-aperture telescopes in China and Ukraine. The observations were obtained during closest approach (CA) to the Earth in order to get more observational points and extend observational arc. It is especially important for newly discovered NEAs when high-precision astrometry is required to determine and improve the orbital elements making them recoverable in next apparitions. The latest astrometric results of NEAs observations, particularly for newly discovered ones, are presented and analyzed in order to refine their orbits and estimate possible recovery in next CA. The comparative analysis of astrometric positions and orbital elements were done regarding to International Astronomical Union Minor Planet Center database and JPL's HORIZONS ephemerides system. The residual differences (O – C) often show high values for newly discovered NEAs during observation date which explained by lack of available observations for reliable calculations of ephemerid positions. The data for such NEAs is presented and orbital calculations are done.
Results of determining the Yarkovsky effect parameter for all asteroids with small perihelion distances known by January, 2021 are presented. A comparison is performed with the results obtained earlier based on another approach and presented in the NASA website. For some objects, different observation sets are considered.
Context. Near-earth objects (NEOs), thanks to their proximity, provide a unique opportunity to investigate asteroids with diameters down to dozens of meters. The study of NEOs is also important because of their potential hazard to the Earth. The investigation of small NEOs is challenging from Earth as they are observable only for a short time following their discovery and can sometimes only be reached again years or decades later.
Aims. We aim to derive the visible colors of NEOs and perform an initial taxonomic classification with a main focus on smaller objects and recent discoveries.
Methods. Photometric observations were performed using the 1.2 m telescope at the Haute-Provence observatory and the 1.0 m telescope at the Pic du Midi observatory in broadband Johnson-Cousins and Sloan photometric systems.
Results. We present new photometric observations for 55 NEOs. Our taxonomic classification shows that almost half (43%) of the objects in our sample are classified as S+Q-complex members, 19% as X-complex, 16% as C-complex, 12% as D-types, and finally 6% and 4% as A- and V-types, respectively. The distribution of the observed objects with H > 19 and H ≤ 19 remains almost the same. However, the majority of the objects in our dataset with D < 500 m belong to the “silicate” group, which is probably a result of an observational bias towards brighter and more accessible objects. “Carbonaceous” objects are predominant among those with a Jovian Tisserand parameter of Tj < 3. These bodies could be dormant or extinct comets. The median values of the absolute magnitude for “carbonaceous” and “silicate” groups are H = 18.10 ± 0.95 and H = 19.50 ± 1.20, whereas the estimated median diameters are D = 1219 ± 729 m and D = 344 ± 226 m, respectively. “Silicate” objects have a much lower median Earth’s minimum orbit intersection distance (MOID) and a somewhat lower orbital inclination in comparison to “carbonaceous” objects. About half of the observed objects are potentially hazardous asteroids and are mostly (almost 65%) represented by “silicate” objects.
Context. The near-Earth objects (NEOs), whose proximity makes them the most accessible bodies in the Solar System, allow us to sample asteroids from tens of kilometers down to objects of a few meters in size. However, while the physical properties for the largest bodies are mostly known, we have very little physical information regarding the small NEOs. These objects today represent the overall majority among the ~2500 new discoveries each year, but they are usually only bright enough to be observable during their close approaches.
Aims. Our aim was to extend our survey that started in 2015 on the NEO population, using ground-based observations to characterize the fainter (and typically smaller) NEOs observable each night.
Methods. We performed BVRIz photometry of NEOs, making use of the DOLORES instrument at the Telescopio Nazionale Galileo (TNG, La Palma, Spain) and the Asiago Schmidt telescope (Italy), in order to derive visible color indexes and the taxonomic classification for each target in our sample.
Results. We taxonomically classified 51 new NEOs for the first time. Together with data obtained in our previous work and collected by other surveys available online, we analyzed an extended sample of 1081 individual NEOs. While the overall majority of them belong to the S-complex, our analysis of the taxonomic distribution found a larger contribution for dark bodies going toward larger H, suggesting that they could be more abundant among the fainter NEOs. Moreover, we find an interesting correlation between semi-major axis and diameter, which could be in part related to the Yarkovsky effect. Rapid characterization of the fainter NEO population shortly after their discovery will be crucial in the future, before those bodies become too faint to be observed, or lost forever.
One possible means of counteraction against a hazardous asteroid is discussed: destruction of the object with a nuclear device during an earlier encounter with the Earth. This is feasible, since virtually all hazardous asteroids appear in near-Earth space several times before they hit the Earth. Computations show that this method is effective and essentially harmless if certain conditions are satisfied. Two possibilities are acceptable. In the first, a spacecraft overtakes the asteroid in a heliocentric orbit. In the second, the asteroid overtakes the spacecraft, which demands a substantially lower characteristic geocentric velocity for the spacecraft. This method for eliminating this cosmic threat is reasonable in two cases: when it is not possible to achieve a soft departure of the object from the collision orbit, and when the object continuously returns to the Earth. A soft departure from a collision orbit can be required multiple times, whereas the destruction of such an object must occur only once.
We have observed three near-Earth objects (NEOs), 2017 VR12, Camillo and Midas, during 2018. The observations were made with the 1-m telescope, operated by Yunnan Observatories, over two nights. Their precise astrometric positions are derived from 989 CCD observations. The theoretical positions of asteroids are retrieved from the Jet Propulsion Laboratory (JPL) Horizons System and Institut de Mécanique Céleste et de Calcul des Éphémérides (IMCCE). The positions of three asteroids are measured with respect to stars in the Gaia DR2 star catalog. For 2017 VR12, the means ( O − C ) of right ascension and declination are −0.090′′ and −0.623′′ respectively based on the published JPL ephemeris, but the correspondingmeans ( O − C ) are 3.122′′ and −0.636′′ based on the published IMCCE ephemeris. The great difference in declination could be explained by several factors. (1) The degraded CCD images caused by the fast apparent motion of the objects lead to a reduction in positioning accuracy. (2) The poor timing system may introduce systematic errors, especially in the high speed direction. (3) The asteroid may be perturbed by Earth when it approaches the Earth too closely. These astrometric results demonstrate that the centroid centering method can reduce the dispersion of non-Gaussian images as compared with the PSF modeling method. For Camillo and Midas, the astrometric results are consistent based on the two ephemerides. Implementing a high-precision timing system, and analyzing some astronomical effects and geometric distortions in CCD images should be carefully considered in future works.
We investigate surface changes near two lunar craters formed on March 17 and September 11, 2003, using high-resolution imagery data (0.5 m/pixel) of the LRO narrow angle camera. The phase- and temporal ratio techniques are applied. Using these techniques reveals a slight “butterfly-wings” pattern around the March 17 crater. This pattern is not seen on usual brightness images. The observed dark halos around the craters may be formed by thin deposits of vapor products at the impacts. Rough estimates show that only 100 g of the nano-phase iron (npFe⁰) is needed to generate the darkening effect, if the iron is spread in a layer of 10 nm thickness on an area with a radius of 70 m. A portion of the ejected materials is seen around the craters as dark and bright splotches. The dark splotches could be produced when excavated material interacts with the cloud of evaporated substance and then falls down to the surface.
Context . The near-Earth object (NEO) population is a window into the original conditions of the protosolar nebula, and has the potential to provide a key pathway for the delivery of water and organics to the early Earth. In addition to delivering the crucial ingredients for life, NEOs can pose a serious hazard to humanity since they can impact the Earth. To properly quantify the impact risk, physical properties of the NEO population need to be studied. Unfortunately, NEOs have a great variation in terms of mitigation-relevant quantities (size, albedo, composition, etc.) and less than 15% of them have been characterized to date.
Aims . There is an urgent need to undertake a comprehensive characterization of smaller NEOs ( D < 300 m) given that there are many more of them than larger objects; their small sizes make them intrinsically fainter and therefore harder to study. One of the main aims of the NEOShield-2 project (2015–2017), financed by the European Community in the framework of the Horizon 2020 program, is therefore to retrieve physical properties of a wide number of NEOs in order to design impact mitigation missions and assess the consequences of an impact on Earth.
Methods . We carried out visible photometry of NEOs, making use of the DOLORES instrument at the Telescopio Nazionale Galileo (TNG, La Palma, Spain) in order to derive visible color indexes and the taxonomic classification for each target in our sample.
Results . We attributed for the first time the taxonomical complex of 67 objects obtained during the first year of the project. While the majority of our sample belong to the S-complex, carbonaceous C-complex NEOs deserve particular attention. These NEOs can be located in orbits that are challenging from a mitigation point of view, with high inclination and low minimum orbit intersection distance (MOID). In addition, the lack of carbonaceous material we see in the small NEO population might not be due to an observational bias alone.
We present the results of the first-ever visible spectroscopic survey fully dedicated to the small (absolute magnitude H>20) near-Earth asteroid (NEA) population. Observations have been performed at the New Technology Telescope (NTT) of the European Southern Observatory (ESO), during a 30-night Guaranteed Time Observations programme, in the framework of the European Commission financed NEOShield-2 project. The visible spectra of 147 objects have been obtained and taxonomically classified. They show a peculiar taxonomic distribution, with respect to larger NEAs. In particular, olivine-rich A-types and organic-rich D-types are more abundant than what could be expected by extrapolating the taxonomic distribution of larger NEAs. Such results have implications for the investigation of the first phases of solar system history, including the delivery of prebiotic material on the early Earth. Having been obtained over a large range of solar phase angles, our data allowed us to evidence peculiar phase reddening behaviours for asteroids belonging to different taxonomic types. Low-albedo asteroids display no or limited phase reddening, compared to moderate- and high-albedo objects. This result suggests a promising novel way to distinguish primitive asteroids in the X-complex. In agreement with previous laboratory experiments, olivine-rich surfaces are the most affected by phase reddening.
Volume 1 of this report discusses overarching trends in the space sector, their drivers, and their implications. Chapters 2 through 8 of this volume focuses on important trends within seven individual subsectors: Earth observation; communication satellite services; space science and technology (S&T) and exploration; launch and access to space; position, navigation, and timing (PNT); human space flight; and space situational awareness (SSA). Chapter 9 looks at current developments in small satellites, which experts believe have the potential to disrupt current trends across sectors. Finally, in Chapter 10, the STPI team speculates on potential “wildcards”—technological, geopolitical, and other unexpected developments—that could disrupt trends. This volume also includes the methodological appendixes referred to in Volume 1 of the report.
The present near-Earth asteroids (NEA) discovery rate has surpassed 1500 objects per year, thus calling for extensive observation campaigns devoted to physical characterization in order to define successful mitigation strategies in case of possible impactors. A tool is presented which, through a prioritization algorithm, aims to optimize the planning and the execution of NEA physical observations. Two ranking criteria are introduced, Importance and Urgency, accounting for the need of satisfying the two basic observational modes for physical characterization, that is, rapid response and large observing programs, aimed at selecting targets for exploration and mitigation space missions. The resulting tool generates a daily table of observable targets and it can also be run as a stand-alone tool in order to provide future observing opportunities at a specific date of interest. It has been developed and implemented within the framework of the NEOShield-2 EU/HORIZON 2020 Project; the output of the prioritization algorithm is publicly available, in tabular format, on the NEOShield-2 NEO Properties Portal (http://www.neoshield.net/the-neoshield-project/project-activities/neo-properties-portal), reachable from the main page of the Project website (http://www.neoshield.eu).
The impact of a near-Earth object (NEO) may release large amounts of energy and cause serious damage. Several NEO hazard studies conducted over the past few years provide forecasts, impact probabilities and assessment ratings, such as the Torino and Palermo scales. These high-risk NEO assessments involve several criteria, including impact energy, mass, and absolute magnitude. The main objective of this paper is to provide the first Multi-Criteria Decision Making (MCDM) approach to classify hazardous NEOs. Our approach applies a combination of two methods from a widely utilized decision making theory. Specifically, the Analytic Hierarchy Process (AHP) methodology is employed to determine the criteria weights, which influence the decision making, and the Technique for Order Performance by Similarity to Ideal Solution (TOPSIS) is used to obtain a ranking of alternatives (potentially hazardous NEOs). In addition, NEO datasets provided by the NASA Near-Earth Object Program are utilized. This approach allows the classification of NEOs by descending order of their TOPSIS ratio, a single quantity that contains all of the relevant information for each object.
Editor: R.D. van der Hilst Keywords: nucleobases Murchison meteorite carbon isotope extraterrestrial organic molecules origin of life Carbon-rich meteorites, carbonaceous chondrites, contain many biologically relevant organic molecules and delivered prebiotic material to the young Earth. We present compound-specific carbon isotope data indicating that measured purine and pyrimidine compounds are indigenous components of the Murchison meteorite. Carbon isotope ratios for uracil and xanthine of δ 13 C = +44.5‰ and +37.7‰, respectively, indicate a non-terrestrial origin for these compounds. These new results demonstrate that organic compounds, which are components of the genetic code in modern biochemistry, were already present in the early solar system and may have played a key role in life's origin.
Longo G.: "The Tunguska event" . Chapter 18, pp. 303-330 in the book: "Comet/Asteroid Impacts and Human Society, An Interdisciplinary Approach, Bobrowsky, Peter T.; Rickman, Hans (Eds.)." , 546 p., © Springer-Verlag, Berlin Heidelberg New York, 2007
In the early morning of 30th June 1908, a powerful explosion over the basin of the Podkamennaya Tunguska River (Central Siberia), devastated 2 150 ± 50 km2 of Siberian taiga. Eighty millions trees were flattened, a great number of trees and bushes were burnt in a large part of the explosion area. Eyewitnesses described the flight of a fire ball, bright as the sun. Seismic and pressure waves were recorded in many observatories throughout the world. Bright nights were observed over much of Eurasia. These different phenomena, initially considered non-correlated, were subsequently linked together as different aspects of the Tunguska event (TE).
On the territory of Russian Federation the Chelyabinsk event was the
biggest and the most dramatic observed LL5 chondrite meteorite fall
since the Tunguska event. For a moment 99% of the main mass was not
found and probably presents atmospheric loss.
Context. The potentially hazardous asteroid (99942) Apophis, previously
designated 2004 MN4, is emblematic of the study of asteroids
that could impact the Earth in the near future. Orbit monitoring and
error propagation analysis are mandatory to predict the probability of
an impact and, furthermore, its possible mitigation. Several aspects for
this prediction have to be investigated, in particular the orbit
adjustment and prediction updates when new astrometric data are
available. Aims: We analyze Apophis orbit and provide impact
predictions based on new observational data, including several orbit
propagations. Methods: New astrometric data of Apophis have been
acquired at the Pic du Midi one-meter telescope (T1m) during March 2011.
Indeed, this asteroid was again visible from ground-based stations after
a period of several years of unfavorable conjunction with the Sun. We
present here the original astrometric data and reduction, and the new
orbit obtained from the adjustment to all data available at Minor Planet
Center (until March 2011). Results: We present a new sketch of
keyholes and impacts for the next century. Additionally, we discuss
observational errors, astrometric reduction, orbit adjustment, and
adequacy of the dynamical model used.
Based on observations made at Pic du Midi station and data from IAU-MPC.
When an asteroid experiences an impact, its path is changed. How much it changes is important to know for both asteroid evolution studies and for attempts to prevent an asteroid from impacting the Earth. In an impact process the total momentum of the material is conserved. However, not all of the material is of interest, but only that remaining with the asteroid. The ratio of the change of momentum of the remaining asteroid to that of the impactor is called the momentum multiplication factor; and is commonly given the symbol β. It has been known for some time that β can be greater than unity, and in some cases far greater. That could be a significant factor in attempts to deflect an asteroid with an impact, and can also be important in the stirring of objects in the asteroid belt due to mutual impacts.The escaping crater ejecta are the source of the momentum multiplication. Housen and Holsapple (Housen, K.R., Holsapple, K.A. [2011a]. Icarus 211, 856–875) have given a recent summary of ejecta characteristics and scaling. Here we use those ejecta results to determine how β depends on the impactor properties, on the asteroid size and composition, and establish the paths and time of flight of all of the ejecta particles. The approach is to add the contribution of each element of ejected mass accounting for its initial velocity, its trajectory and whether it escapes the asteroid. The goal in this paper is to provide a theoretical framework of the fundamental results which can be used as a test of the veracity of experiments and detailed numerical calculations of impacts. A subsequent paper will present direct laboratory results and numerical simulations of momentum multiplication in various geological materials.
Asteroids represent a geophysical frontier of considerable scientific importance, for these building blocks of planets preserve a compositional and mechanical record of the solar system's origin. They also pose a formidable hazard to life on Earth, while offering potentially enormous resources to benefit solar system exploration. This chapter introduces their geologic subtlety through the theme of strength vs. gravity: Asteroids stand apart from rocks and planets because these primary forces (strength short-range and gravity long-range) achieve an intricate mechanical balance that is only partly understood. Recent findings have turned Earth-based intuition on its head. For example, structurally weak asteroids and comets may, through stress dissipation, be the most highly resistant to catastrophic disruption. Perhaps more surprising, the collisional evolution of bodies the size of a city block may be determined by their minuscule self-gravity. While the fundamental geophysical behavior of asteroids continues to elude us, one idea resonates: Instead of competing for dominance, strength and gravity collaborate over a wide spectrum of sizes and shapes to produce some of the richest structures in nature.
Non-gravitational perturbations, regardless being many orders of magnitude weaker than gravity, hold keys to fully understand the evolution of small Solar System bodies. This is because individual bodies, or their entire groups, manifest traces of a long-term accumulated changes by these effects.For meteoroids and small asteroids in the 10 cm-10 km size range, the principal non-gravitational force and torque arise from an anisotropic thermal emission of the absorbed solar radiation. Related perturbations of the orbital and rotational motion are called the Yarkovsky and YORP effects.We review the most important Yarkovsky- and YORP-driven processes, in the Main Asteroid Belt. These include: steady and size-dependent semimajor axis drift, secular changes of rotational period and obliquity, efficient transport towards low-order resonances, interaction with weaker higher-order resonances, captures in secular and spin-orbit resonances.Many independent observations can be naturally interpreted in the framework of Yarkov-sky/YORP models, like cosmic ray exposure ages of meteorites, current population and size-distribution of near-Earth objects, the existence of unstable resonant asteroids or the structure of asteroid families.
Asteroids and comets on orbits with perihelion distance q < 1.3 AU and aphelion distance Q > 0.983 AU are usually called near-Earth objects (NEOs). It has long been debated whether the NEOs are mostly of asteroidal or cometary origin. With improved knowledge of resonant dynamics, it is now clear that the asteroid belt is capable of supplying most of the observed NEOs. Particular zones in the main belt provide NEOs via powerful and diffusive resonances. Through the numerical integration of a large number of test asteroids in these zones, the pos- sible evolutionary paths of NEOs have been identified and the statistical properties of NEOs dynamics have been quantified. This work has allowed the construction of a steady-state model of the orbital and magnitude distribution of the NEO population, dependent on parameters that are quantified by calibration with the available observations. The model accounts for the exist- ence of ~1000 NEOs with absolute magnitude H < 18 (roughly 1 km in size). These bodies carry a probability of one collision with the Earth every 0.5 m.y. Only 6% of the NEO popu- lation should be of Kuiper Belt origin. Finally, it has been generally believed that collisional activity in the main belt, which continuously breaks up large asteroids, injects a large quantity of fresh material into the NEO source regions. In this manner, the NEO population is kept in steady state. The steep size distribution associated with fresh collisonal debris, however, is not observed among the NEO population. This paradox might suggest that Yarkovsky thermal drag, rather than collisional injection, plays the dominant role in delivering material to the NEO source resonances.
The ESO/MPG WFI and the INT WFC wide field archives comprising 330,000 images
were mined to search for serendipitous encounters of known Near Earth Asteroids
(NEAs) and Potentially Hazardous Asteroids (PHAs). A total of 152 asteroids (44
PHAs and 108 other NEAs) were identified using the PRECOVERY software, their
astrometry being measured on 761 images and sent to the Minor Planet Centre.
Both recoveries and precoveries were reported, including prolonged orbital arcs
for 18 precovered objects and 10 recoveries. We analyze all new opposition data
by comparing the orbits fitted before and after including our contributions. We
conclude the paper presenting Mega-Precovery, a new online service focused on
data mining of many instrument archives simultaneously for one or a few given
asteroids. A total of 28 instrument archives have been made available for
mining using this tool, adding together about 2.5 million images forming the
Mega-Archive.
In Plants and the K-T Boundary, two of the world's leading experts in palynology and paleobotany provide a comprehensive account of the fate of land plants during the ‘great extinction’ about 65 million years ago. They describe how the time boundary between the Cretaceous and Paleogene Periods (the K-T boundary) is recognized in the geological record, and how fossil plants can be used to understand global events of that time. There are case studies from over 100 localities around the world, including North America, China, Russia and New Zealand. The book concludes with an evaluation of possible causes of the K-T boundary event and its effects on floras of the past and present. This book is written for researchers and students in paleontology, botany, geology and Earth history, and everyone who has been following the course of the extinction debate and the K-T boundary paradigm shift.
The short dynamical lifetime of near-Earth objects (NEOs) compared to the age of the Solar System implies the existence of sources of replenishment in order to maintain the observed population of NEOs. Main belt asteroids and Jupiter family comets (JFCs), which can end up in typical NEO orbits via planetary perturbations and non-gravitational forces, are the most important sources of replenishment of NEOs. JFCs that become NEOs suffer accelerated loss of their near-surface volatiles, evolving into inactive "dormant" or "extinct" comets that are observationally indistinguishable from low albedo asteroids. Dynamically, however, they retain "comet-like" orbital characteristics. Knowledge of the fraction of extinct comets in the NEO population is important for assessing the amount of cometary material that has been transported to Earth. Furthermore, identifying inactive comet candidates facilitates detailed investigations of the final phase of comet evolution. We present an independent analysis of the fraction of former cometary objects in the NEO population. Due to the large number of NEOs we use a statistical approach to identify dormant or extinct comets based on dynamical and physical properties. We utilize (1) the Tisserand parameter with respect to Jupiter, (2) the minimum orbit intersection distance with respect to Jupiter and (3) albedo measurements. Our albedos are determined from thermal-IR observations made by the Warm Spitzer Space Telescope Exploration Science project "ExploreNEOs", using thermal modeling. The main goal of this work is to estimate the fraction of dormant or extinct comets in the NEO population. We will further provide a list of former comet candidate objects and assess their accessibility with spacecraft via the delta-V parameter. We enhance our investigation by adding data from the literature to our sample and compare our results to earlier published works based on independent analyses. MM acknowledges support by the DFG SPP 1385.
The primary objective of the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) mission is to return pristine samples of carbonaceous material from the surface of a primitive asteroid. The target asteroid, near-Earth object (101955) Bennu, is the most exciting, accessible, and volatile- and organic-rich remnant from the early Solar System. OSIRIS-REx returns a minimum of 60 g of bulk regolith and a separate 26 cm2of fine-grained surface material from this body. Analyses of these samples provide unprecedented knowledge about presolar history, from the initial stages of planet formation to the origin of life. Prior to sample acquisition, OSIRIS-REx performs comprehensive global mapping of the texture, mineralogy, and chemistry of Bennu, resolving geological features, revealing its geologic and dynamic history, and providing context for the returned samples. The instruments also document the regolith at the sampling site in situ at scales down to the sub-centimeter. In addition, OSIRIS-REx studies the Yarkovsky effect, a non-Keplerian force affecting the orbit of this potentially hazardous asteroid (PHA), and provides the first ground truth for telescopic observations of carbonaceous asteroids.
Several competing techniques have been proposed for deflecting NEOs (Near Earth Objects) on potential collision courses with Earth. This paper summarizes recent efforts to develop the NOMAD (NEO Objective Mitigation Analysis Decider) process as a method to compare different NEO mitigation options. NOMAD is the combination of two previously developed processes, ROSETTA (Reduced-Order Simulation for Evaluation of Technologies and Transportation Architectures) modeling and TOPSIS (Technique for Order Preference by Similarity to Ideal Solution). ROSETTA modeling is used to simulate each mitigation option from technology development through mission completion based on consistent methodologies and common analysis assumptions. The ROSETTA model generates values for in-space stage and mitigation vehicle masses, development and deployment costs, and momentum imparted to the NEO. These results are then used by TOPSIS to rank the different mitigation options with six figures of merit: effectiveness, applicability, technology readiness, research and development degree of difficulty, development cost, and deployment cost. Multiple weighting scenarios between these figures of merit are considered to display the flexibility of this ranking system based on different decision-making priorities. In this study, six mitigation options are evaluated against three different NEO test cases. The results of these evaluations are presented with four TOPSIS weighting scenarios.
The Near Earth Object Camera (NEOCam) is a proposed space mission
designed to discover and characterize most of the potentially hazardous
asteroids that orbit near the Earth. NEOCam consists of an infrared
telescope and a passively cooled wide-field camera operating at thermal
infrared wavelengths. NASA has funded technology development for NEOCam,
including the development of long wavelength infrared detector arrays
that will have excellent performance at NEOCam’s zodiacal
emission-limited background. Teledyne Imaging Sensors has developed and
delivered for test at the University of Rochester the first set of
approximately 10 micron cutoff, 1024 x 1024 HgCdTe detector arrays in
accord with NEOCam requirements. The first measurements of these arrays
show the development to be extremely promising: noise, dark current,
quantum efficiency and well depth goals have been met by this technology
at focal plane temperatures of 40K, readily attainable with passive
cooling. The next set of arrays to be developed will address changes
suggested by the first set of deliverables.
The near Earth asteroid (99942) Apophis, discovered in 2004, (with an
approximately diameter of 270 meter) will come back very close to the
Earth on April 13, 2029. During its 2029 pass, Apophis will present an
unique opportunity for study its characterization and investigate
possible mitigation techniques. The object will be easily visible from
the Earth and it can be expected that its geometry and thermal
properties will be well determined from ground based observations.
However, the characterization of its interior will not be achievable
from purely terrestrial observations. Such a characterization, beyond
its high scientific value, is essential for planning any mitigation
operation, should it be necessary in the future. Near Earth objects are
a precious source of information as they represent a mixture of
different population of small bodies containing fundamental issues on
the origin and early evolution of the solar system. The accretion
mechanism plays a major role in the formation of the planets of the
solar system. These small bodies are believed in fact to be the remnants
of the swarm of planetesimals from which the planets were formed.
Monitoring the response of this asteroid to the gravitational
constraints induced by its close approach to the Earth will permit to
characterize its internal structure. A study to identify some affordable
mission scenario for such a mission is presently underway at CNES (the
French Space Agency). The paper will present the scientific and
mitigation objectives of the mission as well as the preliminary results
of the mission analysis and the main system characteristics.
The short dynamical lifetime of near-Earth objects (NEOs) compared to
the age of the Solar System implies the existence of sources of
replenishment in order to maintain the observed population of NEOs. Main
belt asteroids and Jupiter family comets (JFCs), which can end up in
typical NEO orbits via planetary perturbations and non-gravitational
forces, are the most important sources of replenishment of NEOs. JFCs
that become NEOs suffer accelerated loss of their near-surface
volatiles, evolving into inactive "dormant" or "extinct" comets that are
observationally indistinguishable from low albedo asteroids.
Dynamically, however, they retain "comet-like" orbital characteristics.
Knowledge of the fraction of extinct comets in the NEO population is
important for assessing the amount of cometary material that has been
transported to Earth. Furthermore, identifying inactive comet candidates
facilitates detailed investigations of the final phase of comet
evolution. We present an independent analysis of the fraction of former
cometary objects in the NEO population. Due to the large number of NEOs
we use a statistical approach to identify dormant or extinct comets
based on dynamical and physical properties. We utilize (1) the Tisserand
parameter with respect to Jupiter, (2) the minimum orbit intersection
distance with respect to Jupiter and (3) albedo measurements. Our
albedos are determined from thermal-IR observations made by the Warm
Spitzer Space Telescope Exploration Science project "ExploreNEOs", using
thermal modeling. The main goal of this work is to estimate the fraction
of dormant or extinct comets in the NEO population. We will further
provide a list of former comet candidate objects and assess their
accessibility with spacecraft via the delta-V parameter. We enhance our
investigation by adding data from the literature to our sample and
compare our results to earlier published works based on independent
analyses. MM acknowledges support by the DFG SPP 1385.
NEO surveys have now achieved, more or less, the “Spaceguard
Goal” of cataloging 90% of NEAs larger than 1 km in diameter, and
thereby have reduced the short-term hazard from cosmic impacts by about
an order of magnitude, from an actuarial estimate of 1,000 deaths per
year (actually about a billion every million years, with very little in
between), to about 100 deaths per year, with a shift toward smaller but
more frequent events accounting for the remaining risk. It is fair to
ask, then, what is the value of a next-generation accelerated survey to
“retire” much of the remaining risk. The curve of completion
of survey versus size of NEA is remarkably similar for any survey,
ground or space based, visible light or thermal IR, so it is possible to
integrate risk over all sizes, with a time variable curve of completion
to evaluate the actuarial value of speeding up survey completion. I will
present my latest estimate of NEA population and completion of surveys.
From those I will estimate the “value” of accelerated
surveys such as Pan-STARRS, LSST, or space-based surveys, versus
continuing with current surveys. My tentative conclusion is that we may
have already reached the point in terms of cost-benefit where
accelerated surveys are not cost-effective in terms of reducing impact
risk. If not yet, we soon will. On the other hand, the surveys, which
find and catalog main-belt and other classes of small bodies as well as
NEOs, have provided a gold mine of good science. The scientific value of
continued or accelerated surveys needs to be emphasized as the impact
risk is increasingly “retired.”
The Asteroid Terrestrial-impact Last Alert System (ATLAS) could survey
the entire visible night sky to V 20 four times each night to detect
asteroids on an Earth-impacting trajectory. We plan on using existing
image analysis and moving object detection software; mostly
off-the-shelf telescopes, mounts and observatories; and readily
available computation and data storage nodes. We will present our survey
simulations showing the evolution of the impact probability for objects
on an impact trajectory as a function of time before impact for
different ATLAS implementations. e.g. with two observatories at one
location or separated by about 100 km. ATLAS should provide about a
month's advance notice of impact for 300m diameter objects and about a
week's notice for Tunguska scale impactors of 50m diameter.
We present estimates of momentum transfer by ablation and β
factor-like ejection of solid material from the surface of a Potentially
Hazardous Object (PHO) by a stand-off nuclear burst. We consider
parameters including object composition, shadowing effects of surface
geometry, burst yield, and stand-off distance. We use radiation
hydrocode models of x-ray energy deposition to estimate the response of
a PHO to x-rays. We also use Monte Carlo models to estimate energy
deposition from neutrons. These models yield estimates of the mass of
vapor and solid material ejected from the surface of the PHO. A
byproduct of the Monte Carlo models is an estimate of neutron activation
of PHO material, a commonly quoted hazard of nuclear PHO deflection,
which is negligible, of order tens of micrograms per kiloton of burst
yield. The mass vaporized or ejected from the PHO, along with initial
distributions and velocities can then be used to refine n-body models of
velocity change and debris reaggregation.
Various methods have been proposed to avoid the collision of a Near-Earth Object (NEO) with the Earth. Each of these methods relies on a mitigation concept (deflection or fragmentation), an energy source (e.g. kinetic, gravitational, solar, thermal, etc.) and a mode of approach (e.g. remote station and interaction). The efficiency of each method depends on the physical properties of the considered NEO that influence the way the body will respond to the considered energy source. While the knowledge of properties such as the mass, spin rate and obliquity as well as the shape is generally required for all mitigation methods, there are other properties that are important to know for some methods and that have no great influence for other ones. This paper summarizes the current knowledge of main physical properties of NEOs and their importance for the most usual mitigation strategies that have been proposed, i.e. the kinetic impactor, the gravity tractor, strategies based on anchoring or depositing material on the surface, and strategies aimed at modifying the thermal properties of the NEO in order to either modify or cancel the Yarkovsky effect, or cause surface vaporization.
Although discussions are underway within the Action Team 14 of the United Nations COPUOS, there is currently no concerted international plan addressing the impact threat from near-Earth objects (NEOs) and how to organize, prepare and implement mitigation measures. We report on a new international project to address impact hazard mitigation issues, being the subject of a proposal submitted to the European Commission in response to the 2011 FP7 Call “Prevention of impacts from near-Earth objects on our planet”. Our consortium consists of 13 research institutes, universities, and industrial partners from 6 countries and includes leading US and Russian space organizations. The primary aim of the project, NEOShield, is to investigate in detail the three most promising mitigation techniques: the kinetic impactor, blast deflection, and the gravity tractor, and devise feasible demonstration missions. Furthermore, we will investigate options for an international strategy for implementation when an actual impact threat arises.The NEOShield project was formally accepted by the European Commission on 17 November 2011 and funded with a total of 5.8 million Euros for a period of 3.5 years. The kick-off meeting took place at the DLR Institute of Planetary Research, Berlin, in January 2012. In this paper we present a brief overview of the planned scope of the project.
Near-Earth Asteroids (NEAs) offer insight into a size range of objects that are not easily observed in the main asteroid belt. Previous studies on the diversity of the NEA population have relied primarily on modeling and statistical analysis to determine asteroid compositions. Olivine and pyroxene, the dominant minerals in most asteroids, have characteristic absorption features in the visible and near-infrared (VISNIR) wavelengths that can be used to determine their compositions and abundances. However, formulas previously used for deriving compositions do not work very well for ordinary chondrite assemblages. Because two-thirds of NEAs have ordinary chondrite-like spectral parameters, it is essential to determine accurate mineralogies. Here we determine the band area ratios and Band I centers of 72 NEAs with visible and near-infrared spectra and use new calibrations to derive the mineralogies 47 of these NEAs with ordinary chondrite-like spectral parameters. Our results indicate that the majority of NEAs have LL-chondrite mineralogies. This is consistent with results from previous studies but continues to be in conflict with the population of recovered ordinary chondrites, of which H chondrites are the most abundant. To look for potential correlations between asteroid size, composition, and source region, we use a dynamical model to determine the most probable source region of each NEA. Model results indicate that NEAs with LL chondrite mineralogies appear to be preferentially derived from the ν6 secular resonance. This supports the hypothesis that the Flora family, which lies near the ν6 resonance, is the source of the LL chondrites. With the exception of basaltic achondrites, NEAs with non-chondrite spectral parameters are slightly less likely to be derived from the ν6 resonance than NEAs with chondrite-like mineralogies. The population of NEAs with H, L, and LL chondrite mineralogies does not appear to be influenced by size, which would suggest that ordinary chondrites are not preferentially sourced from meter-sized objects due to Yarkovsky effect.
A significant portion of the Solar System’s population of minor bodies may be quite porous. A unique aspect of crater formation in porous bodies is that large craters may form without the ejecta deposits that are associated with craters on less porous bodies. In this paper, laboratory experiments and scaling theories are used to identify the conditions under which ejecta deposits are suppressed. The results are consistent with the interpretation that large craters on asteroid Mathilde (porosity ∼50%) and Saturn’s moon Hyperion (porosity >40%) apparently formed without producing significant ejecta deposits, while smaller bodies do have notable regoliths.
We observed near-Earth Asteroid (8567) 1996 HW1 at the Arecibo Observatory on six dates in September 2008, obtaining radar images and spectra. By combining these data with an extensive set of new lightcurves taken during 2008–2009 and with previously published lightcurves from 2005, we were able to reconstruct the object’s shape and spin state. 1996 HW1 is an elongated, bifurcated object with maximum diameters of 3.8 × 1.6 × 1.5 km and a contact-binary shape. It is the most bifurcated near-Earth asteroid yet studied and one of the most elongated as well. The sidereal rotation period is 8.76243 ± 0.00004 h and the pole direction is within 5° of ecliptic longitude and latitude (281°, −31°). Radar astrometry has reduced the orbital element uncertainties by 27% relative to the a priori orbit solution that was based on a half-century of optical data. Simple dynamical arguments are used to demonstrate that this asteroid could have originated as a binary system that tidally decayed and merged.
Canada’s Near-Earth Object Surveillance Satellite (NEOSSat), set to launch in early 2012, will search for and track Near-Earth Objects (NEOs), tuning its search to best detect objects with a < 1.0 AU. In order to construct an optimal pointing strategy for NEOSSat, we needed more detailed information in the a < 1.0 AU region than the best current model (Bottke, W.F., Morbidelli, A., Jedicke, R., Petit, J.M., Levison, H.F., Michel, P., Metcalfe, T.S. [2002]. Icarus 156, 399–433) provides. We present here the NEOSSat-1.0 NEO orbital distribution model with larger statistics that permit finer resolution and less uncertainty, especially in the a < 1.0 AU region. We find that Amors = 30.1 ± 0.8%, Apollos = 63.3 ± 0.4%, Atens = 5.0 ± 0.3%, Atiras (0.718 < Q < 0.983 AU) = 1.38 ± 0.04%, and Vatiras (0.307 < Q < 0.718 AU) = 0.22 ± 0.03% of the steady-state NEO population. Vatiras are a previously undiscussed NEO population clearly defined in our integrations, whose orbits lie completely interior to that of Venus. Our integrations also uncovered the unexpected production of retrograde orbits from main-belt asteroid sources; this retrograde NEA population makes up ≃0.1% of the steady-state NEO population. The relative NEO impact rate onto Mercury, Venus, and Earth, as well as the normalized distribution of impact speeds, was calculated from the NEOSSat-1.0 orbital model under the assumption of a steady-state. The new model predicts a slightly higher Mercury impact flux.
The earliest bombardment history of the Moon potentially provides powerful constraints for solar system evolution models. A major uncertainty, however, is how much of this history is actually recorded in lunar craters. For example, some argue that most ancient lunar craters and basins were produced by a declining bombardment of leftover planetesimals produced by terrestrial planet formation processes. Others believe that most lunar craters and large basins were formed in a narrow time interval between 3.8 and 4.0 Ga, the so-called lunar cataclysm. In the light of recent improvements in our understanding of early solar system evolution, it is possible that the contributions from both scenarios could be represented in the lunar crater record. If so, when did the declining bombardment end and the lunar cataclysm begin?Here we show, using new counts of 15–150 km diameter craters on the most ancient lunar terrains, that the craters found on or near Nectaris basin appear to have been created by projectiles hitting twice as fast as those that made the oldest craters on various Pre-Nectarian-era terrains. This dramatic velocity increase is consistent with the existence of a lunar cataclysm and potentially with a late reconfiguration of giant planet orbits, which may have strongly modified the source of lunar impactors. This work also suggests that the lunar cataclysm may have started near the formation time of Nectaris basin. This possibility implies that South Pole-Aitken basin (SPA), the largest lunar basin and one of the oldest by superposition, was not created during the cataclysm. This view is strengthened by our interpretation that a substantial fraction of ancient craters on SPA were made by low velocity impactors. Finally, we believe these results shed new light on the impact history of the primordial Earth.
Pan-STARRS is a highly cost-effective, modular and scalable approach to wide-field optical/NIR imaging. It uses 1.8m telescopes with very large (7 square degree) field of view and revolutionary1.4 billion pixel CCD cameras with low noise and rapid read-out to provide broad-band imaging from 400-1000nm wavelength. The first single telescope system, PS1, has been deployed on Haleakala on Maui, and has been collecting science quality survey data for approximately six months. PS1 will be joined by a second telescope PS2 in approximately 18 months. A four aperture system is planned to become operational following the end of the PS1 mission. This will be able to scan the entire visible sky to approximately 24th magnitude in less than a week, thereby meeting the goals set out by the NAS 2000 decadal review for a "Large Synoptic Sky Telescope". Here we review the technical design, and give an update on the progress that has been made with the PS1 system.
We review the results of this dual-hemisphere NEO survey which has been responsible for the majority of new NEO discoveries since 2005. We will discuss the distribution of discovery circumstances, coverage limitations, discovery efficiency, contribution to the spaceguard goal, and ongoing experiments to improve the discovery rate. We find that the ability to make same-night follow up of suspected NEOs aids significantly towards identifying and not losing NEOs. This work is supported by the NASA NEOO Program.
On February 14, 2000, the Near Earth Asteroid Rendezvous spacecraft (NEAR Shoemaker) began the first orbital study of an asteroid, the near-Earth object 433 Eros. Almost a year later, on February 12, 2001, NEAR Shoemaker completed its mission by landing on the asteroid and acquiring data from its surface. NEAR Shoemaker's intensive study has found an average density of 2.67 ± 0.03, almost uniform within the asteroid. Based upon solar fluorescence X-ray spectra obtained from orbit, the abundance of major rock-forming elements at Eros may be consistent with that of ordinary chondrite meteorites except for a depletion in S. Such a composition would be consistent with spatially resolved, visible and near-infrared (NIR) spectra of the surface. Gamma-ray spectra from the surface show Fe to be depleted from chondritic values, but not K. Eros is not a highly differentiated body, but some degree of partial melting or differentiation cannot be ruled out. No evidence has been found for compositional heterogeneity or an intrinsic magnetic field. The surface is covered by a regolith estimated at tens of meters thick, formed by successive impacts. Some areas have lesser surface age and were apparently more recently disturbed or covered by regolith. A small center of mass offset from the center of figure suggests regionally nonuniform regolith thickness or internal density variation. Blocks have a nonuniform distribution consistent with emplacement of ejecta from the youngest large crater. Some topographic features indicate tectonic deformations. Several regional-scale linear features have related orientations, suggesting a globally consolidated internal structure. Structural control of crater shapes hints that such internal structure is pervasive. From the bulk density, inferred composition, and evidence for global structure, Eros is interpreted to be largely intact but extensively fractured.
Direct comparison of ancient extinctions to the present-day situation is difficult, because quantitative palaeontological data come primarily from marine invertebrates, fossilized species are usually drawn from the more abundant and widespread taxa, and time resolution is rarely better than 103-104 years. A growing array of techniques permits quantitative error estimates on some of these potential biases, and allows calculation of species extinction intensities from genus-level data, which are more robust. Extensive as today's species losses probably are, they have yet to equal any of the Big Five mass extinctions. Background extinction patterns are potential sources of insight regarding present-day biotic losses; over 90% of past species extinction has occurred at times other than the Big Five mass extinctions. Mean durations of fossil species vary by more than an order of magnitude even within clades, rendering uninformative any global average for background extinction. Taxon-specific variation is evidently related to intrinsic biotic factors such as geographic range and population size. Approaches to extinction analysis and prediction based on morphological variety or biodisparity should be explored as an adjunct or alternative to taxon inventories or phylogenetic metrics. Rebounds from mass extinctions are geologically rapid but ecologically slow; biodiversity recovery and the re-establishment of some communities typically requires 5-10 million years.
We use recently published coastal population density data [1] and impact-generated tsunami rates [2] to develop a quantitative assessment of the tsunami risk posed by Earth impactors. We find that most tsunami damage can be associated with the more frequent impacts of smaller objects with sizes at or near the atmospheric penetration limit. Fully half of the impact tsunami hazard arises from objects smaller than 300m in diameter. Similarly, half of the tsunami risk stems from waves smaller than 11m high that should run in only 500-1000m from shore. In the mean, one million people are displaced by isolated tsunami events occurring 5200 years apart, and 182 people will be displaced annually by such catastrophes. Error analyses indicate the 90% confidence interval for this result is 59-379 people displaced per year. [1] Small, C., V. Gornitz and J. Cohen, Environmental Geosciences, vol. 7, 3--12 (2000). [2] Ward, S.N. and E. Asphaug, Icarus, vol. 145, 64--78 (2000) .
The Near-Earth Object Camera (NEOCam) is a space-based mid- infrared (IR) observing system, operating at the Earth-Sun L1 point. NEOCam's primary science goals are: - To assess the hazard to Earth from Near-Earth Objects (NEOs) - To study the origin and ultimate fate of our Solar System's asteroids NEOCam consists of a 50 cm telescope passively cooled to 30 K; it is equipped with a single mid-IR bandpass operating from 6 - 10 um. NEOCam will detect 78% of potentially hazardous NEOs >140; m diameter within 5 years. If the mission continues for an additional 5 years, NEOCam will meet NASA's goal of discovering 90% of potentially hazardous objects larger than 140 m in diameter. NEOCam's observation strategy allows it to discover the orbits of new NEOs independently and provide robust diameter measurements for all detections. NEOCam will discover and measure diameters for 100x more NEOs than are currently known today. NEOCam will place the first constraints on the population of asteroids with orbits that are totally interior to the Earth's orbit (IEOs). NEOCam is sensitive to a wide range of albedos and can scan areas of the sky that are difficult to access with ground-based surveys. NEOCam is fundamentally different from visible surveys, since its mid-IR bandpass allows more direct physical characterization of asteroids.
The Lincoln Near-Earth Asteroid Research (LINEAR) program has applied electro-optical technology developed for Air Force Space Surveillance applications to the problem of discovering near-Earth asteroids (NEAs) and comets. This application is natural due to the commonality between the surveillance of the sky for man-made satellites and the search for near-Earth objects (NEOs). Both require the efficient search of broad swaths of sky to detect faint, moving objects. Currently, the Air Force Ground-based Electro-Optic Deep Space Surveillance (GEODSS) systems, which operate as part of the worldwide U.S. space surveillance network, are being upgraded to state-of-the-art charge-coupled device (CCD) detectors. These detectors are based on recent advances made by MIT Lincoln Laboratory in the fabrication of large format, highly sensitive CCDs. In addition, state-of-the-art data processing algorithms have been developed to employ the new detectors for search operations. In order to address stressing space surveillance requirements, the Lincoln CCDs have a unique combination of features, including large format, high quantum efficiency, frame transfer, high readout rate, and low noise, not found on any commercially available CCD. Systems development for the GEODSS upgrades has been accomplished at the Lincoln Laboratory Experimental Test Site (ETS) located near Socorro, New Mexico, over the past several years. Starting in 1996, the Air Force funded a small effort to demonstrate the effectiveness of the CCD and broad area search technology when applied to the problem of finding asteroids and comets. This program evolved into the current LINEAR program, which is jointly funded by the Air Force Office of Scientific Research and NASA. LINEAR, which started full operations in March of 1998, has discovered through September of 1999, 257 NEAs (of 797 known to date), 11 unusual objects (of 44 known), and 32 comets. Currently, LINEAR is contributing ~70% of the worldwide NEA discovery rate and has single-handedly increased the observations submitted to the Minor Planet Center by a factor of 10. This paper covers the technology used by the program, the operations, and the detailed results of the search efforts.
Holsapple [Holsapple, K.A., 2001. Icarus 154, 432 448; Holsapple, K.A., 2004. Icarus 172, 272 303] determined the spin limits of bodies using a model for solid bodies without tensile or cohesive strength, but with the pressure-induced shear strengths characteristic of dry sands and gravels. That theory included the classical analyses for fluid bodies given by Maclaurin, Jacobi and others as a special case. For the general solid bodies, it was shown that there exists a very wide range of permissible shapes and spin limits; and explicit algebraic results for those limits were given. This paper gives an extension of those analyses to include geological-like materials that also have tensile and cohesive strength. Those strengths are necessary to explain the smaller, fast-rotating asteroids discovered in the last few years. I find that the spin limits for these more general solids have two limiting regimes: a strength regime for bodies with a diameter 10 km (which is the case covered by the earlier papers). I derive explicit algebraic forms for the dependence of the spin limits on shape, mass density and material strength properties. The comparison of the theory to the database for the spins of asteroids and trans-neptunian objects (TNO's) objects shows excellent agreement. For large bodies (diameter D>10 km), the presence of cohesive and/or tensile strength does not permit higher spin rates than would be allowed for rubble pile bodies. Thus, the fact that the spin rates of all large bodies is limited to periods greater than about 2 h does not imply that they are rubble piles. In contrast, for small bodies (D
Photon thrust from shape alone can produce quasi-secular changes in an asteroid's orbital elements. An asteroid in an elliptical orbit with a north–south shape asymmetry can steadily alter its elements over timescales longer than one orbital trip about the Sun. This thrust, called here orbital YORP (YORP = Yarkovsky–O'Keefe–Radzievskii–Paddack), operates even in the absence of thermal inertia, which the Yarkovsky effects require. However, unlike the Yarkovsky effects, which produce secular orbital changes over millions or billions of years, the change in an asteroid's orbital elements from orbital YORP operates only over the precession timescale of the orbit or of the asteroid's spin axis; this is generally only thousands or tens of thousands of years. Thus while the orbital YORP timescale is too short for an asteroid to secularly journey very far, it is long enough to warrant investigation with respect to 99942 Apophis, which might conceivably impact the Earth in 2036. A near-maximal orbital YORP effect is found by assuming Apophis is without thermal inertia and is shaped like a hemisphere, with its spin axis lying in the orbital plane. With these assumptions orbital YORP can change its along-track position by up to ±245 km, which is comparable to Yarkovsky effects. Though Apophis' shape, thermal properties, and spin axis orientation are currently unknown, the practical upper and lower limits are liable to be much less than the ±245 km extremes. Even so, the uncertainty in position is still likely to be much larger than the ∼0.5 km “keyhole” Apophis must pass through during its close approach in 2029 in order to strike the Earth in 2036.
Direct comparison of ancient extinctions to the present-day situation is difficult, because quantitative palaeontological data come primarily from marine invertebrates, fossilized species are usually drawn from the more abundant and widespread taxa, and time resolution is rarely better than 10(3)-10(4) years. A growing array of techniques permits quantitative error estimates on some of these potential biases, and allows calculation of species extinction intensities from genus-level data, which are more robust. Extensive as today's species losses probably are, they have yet to equal any of the Big Five mass extinctions. Background extinction patterns are potential sources of insight regarding present-day biotic losses; over 90% of past species extinction has occurred at times other than the Big Five mass extinctions. Mean durations of fossil species vary by more than an order of magnitude even within clades, rendering uninformative any global average for background extinction. Taxon-specific variation is evidently related to intrinsic biotic factors such as geographic range and population size. Approaches to extinction analysis and prediction based on morphological variety or biodisparity should be explored as an adjunct or alternative to taxon inventories or phylogenetic metrics. Rebounds from mass extinctions are geologically rapid but ecologically slow; biodiversity recovery and the re-establishment of some communities typically requires 5-10 million years.
This paper describes the implementation of delta-DOR (delta-differential one-way ranging) receivers within the ESA Deep Space ground station network. Delta-DOR provides very accurate plane-of-sky measurements of spacecraft position which complement existing line-of-sight ranging and Doppler measurements. We discuss how this technique has been adapted and implemented at the two ESA deep-space ground stations using existing equipment and infrastructure. These new capabilities were added by writing new software modules for the standard ESA digital receiver (the intermediate frequency modem system—IFMS). With these upgrades the receiver has the ability to record accurately timetagged signals from up to eight IF sub-channels. These sub-channels can have bandwidths of 50kHz–2MHz with a sample quantization of 1–16 bits per component. The IF samples are stored locally for subsequent retrieval over a WAN by the correlator facility at ESOC.
The physical characterization of the surfaces of Near Earth Objects (NEOs) is crucial to analyse the relationships among NEOs and the other populations of minor bodies of the Solar System (main-belt asteroids, comets and meteorites) and to investigate NEO origin and evolution. Reflectance spectroscopy provides a powerful tool for determining several aspects of the surface composition of atmosphereless bodies. In particular, photometry and spectroscopy in a large wavelength interval (from visible to far-infrared) allow us to characterize the materials present on the surfaces of NEOs and to classify them, depending on the albedo values and the observed spectral behaviour. To cite this article: E. Dotto et al., C. R. Physique 6 (2005).
We explore the hypothesis that, due to small van der Waals forces between
regolith grains, the strength of small rubble pile asteroids is constant. This
creates a scale dependence, with relative strength increasing as size
decreases. This counters classical theory that rubble pile asteroids should
behave as scale-independent cohesionless collections of rocks. We explore a
simple model for asteroid strength that is based on these weak forces, validate
it through granular mechanics simulations and comparisons with properties of
lunar regolith, and then show its implications and ability to explain and
predict observed properties of small asteroids in the NEA and Main Belt
populations. A conclusion is that the population of rapidly rotating asteroids
consists of both distributions of smaller grains (i.e., rubble piles) and of
monolithic boulders whose surfaces may still retain a size distribution of
finer grains, potentially of size up to centimeters.
The so-called Nysa-Polana complex of asteroids is a diverse and widespread
group. It appears to be two overlapping families of different asteroid
taxonomies: (44) Nysa is an E-type asteroid with the lowest number in the midst
of a predominantly S-type cluster and (142) Polana is a B-type asteroid near
the low-albedo B- and C-type cluster.
Using the data from the Wide-field Infrared Survey Explorer (WISE) mission we
have re-analyzed the region around the Nysa-Polana complex in the inner Main
Belt, focusing on the low-albedo population. (142) Polana does not appear to be
a member of the family of low-albedo asteroids in the Nysa-Polana complex.
Rather, the largest is asteroid (495) Eulalia. This asteroid has never before
been linked to this complex for an important dynamical reason: it currently has
a proper eccentricity slightly below the range of most of the family members.
However, its orbit is very close to the 3:1 mean motion resonance with Jupiter
and is in a weak secular resonance. We show that its osculating eccentricity
varies widely on short timescales and the averaged value diffuses over long
timescales. The diffusive orbit, low-albedo, taxonomic similarity and semimajor
axis strongly suggests that despite its current proper eccentricity, (495)
Eulalia could have recently been at an orbit very central to the family.
Hierarchical Clustering Method tests confirm that at an eccentricity of e=0.15,
(495) Eulalia could be the parent of the family. The ``Eulalia family'' was
formed between 900--1500 Myr ago, and likely resulted from the breakup of a
100--160 km parent body. There is also compelling evidence for an older and
more widespread primitive family in the same region of the asteroid belt
parented by asteroid (142) Polana.
We seek evidence of the Yarkovsky effect among Near Earth Asteroids (NEAs) by
measuring the Yarkovsky-related orbital drift from the orbital fit. To prevent
the occurrence of unreliable detections we employ a high precision dynamical
model, including the Newtonian attraction of 16 massive asteroids and the
planetary relativistic terms, and a suitable astrometric data treatment. We
find 21 NEAs whose orbital fits show a measurable orbital drift with a signal
to noise ratio (SNR) greater than 3. The best determination is for asteroid
(101955) 1999 RQ36, resulting in the recovery of one radar apparition and an
orbit improvement by two orders of magnitude. In addition, we find 16 cases
with a lower SNR that, despite being less reliable, are good candidates for
becoming stronger detections in the future. In some cases it is possible to
constrain physical quantities otherwise unknown by means of the detected
orbital drift. Furthermore, the distribution of the detected orbital drifts
shows an excess of retrograde rotators that can be connected to the delivery
mechanism from the most important NEA feeding resonances and allows us to infer
the distribution for NEAs obliquity. We discuss the implications of the
Yarkovsky effect for impact predictions. In particular, for asteroid (29075)
1950 DA our results favor a retrograde rotation that would rule out an impact
in 2880.
We discuss the potential contribution of the Discovery Channel Telescope (or a clone) to a detection program aimed at discovering 90% of potentially hazardous objects (PHOs) larger than 140 m in diameter. Three options are described, each involving different levels of investment. We believe that LSST, Pan-STARRS, and DCT, working in a coordinated fashion, offer a cost-effective, low-risk way to accomplish the objectives of the extended NEO search program.