Space Science Reviews

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Cartoon cross section of a protoplanetary disk. In the inner disk and the upper layers of the outer disk water is in the gas phase. In the cool, outer regions of the disk, water is frozen out as ice on the surface of dust grains. The zone where water transitions between existing primarily in the gas versus the ice is called the water snowline. The snowline at the midplane, where planet formation occurs, is thought to separate the gas giant and terrestrial planet forming regions
Model water spectrum for a protoplanetary disks. OASIS will measure the water vapor content of disks throughout the planet forming region using multiple water transitions that probe both the outer and inner disk, as well as intermediate regions near the snowline. Crucially, OASIS is able to observe the ground-state ortho and para water lines and the J=1-0 transition of HD simultaneously
Flux normalized, disk integrated spectra from a protoplanetary disk model inclined 45 degrees from face-on at 0.9 km s⁻¹ spectral resolution. Emission from disks is Doppler shifted due to Keplerian rotation. Emission with a high velocity offset originates from small radii, while emission close to the systemic velocity originates from large radii. OASIS will leverage this to trace emission in spectrally resolved lines to the radius in the disk where the emitting molecules reside
a) Herschel-HIFI detection of ground-state H2O emission (van Dishoeck et al. 2021), tracing cold water vapor in the outer disk. b) Herschel-PACS spectrum (Riviere-Marichalar et al. 2012) showing unresolved lines targeted by OASIS Band-4. The high energy H2O transition probes gas within the snowline. The strong atomic [OI] line could trace disk winds (Sect. 4.3). c) Herschel-PACS detection of the spectrally unresolved HD J=1-0 line (Bergin et al. 2013a), a key measure of total disk mass (Sect. 4.4). OASIS will provide high-sensitivity velocity-resolved observations of these and other transitions in more than 100 protoplanetary systems
Blue dots show disparity between disk mass estimates based on CO (y axis) and dust continuum (x axis) observations with ALMA. The two mass tracers rarely agree (dashed line), with CO-based measurements, often giving a lower mass. Red dots show the mass derived from the HD 1-0 line. HD observations allow a more direct measurement of gas mass. Due to low integration times and limited sensitivity, Herschel only detected HD in three massive disks. OASIS will measure total gas mass in 100+ protoplanetary systems down to 0.1 Jupiter masses
  • Kamber R. Schwarz
    Kamber R. Schwarz
  • Joan Najita
    Joan Najita
  • Jennifer Bergner
    Jennifer Bergner
  • [...]
  • Christopher K. Walker
    Christopher K. Walker
The Orbiting Astronomical Satellite for Investigating Stellar Systems (OASIS) is a NASA Astrophysics MIDEX-class mission concept, with the stated goal of Following water from galaxies, through protostellar systems, to Earth’s oceans. This paper details the protoplanetary disk science achievable with OASIS. OASIS’s suite of heterodyne receivers allow for simultaneous, high spectral resolution observations of water emission lines spanning a large range of physical conditions within protoplanetary disks. These observations will allow us to map the spatial distribution of water vapor in disks across evolutionary stages and assess the importance of water, particularly the location of the midplane water snowline, to planet formation. OASIS will also detect the H2 isotopologue HD in 100+ disks, allowing for the most accurate determination of total protoplanetary disk gas mass to date. When combined with the contemporaneous water observations, the HD detection will also allow us to trace the evolution of water vapor across evolutionary stages. These observations will enable OASIS to characterize the time development of the water distribution and the role water plays in the process of planetary system formation.
 
Venus is the planet in the Solar System most similar to Earth in terms of size and (probably) bulk composition. Until the mid-20th century, scientists thought that Venus was a verdant world—inspiring science-fictional stories of heroes battling megafauna in sprawling jungles. At the start of the Space Age, people learned that Venus actually has a hellish surface, baked by the greenhouse effect under a thick, CO2-rich atmosphere. In popular culture, Venus was demoted from a jungly playground to (at best) a metaphor for the redemptive potential of extreme adversity. However, whether Venus was much different in the past than it is today remains unknown. In this review, we show how now-popular models for the evolution of Venus mirror how the scientific understanding of modern Venus has changed over time. Billions of years ago, Venus could have had a clement surface with water oceans. Venus perhaps then underwent at least one dramatic transition in atmospheric, surface, and interior conditions before present day. This review kicks off a topical collection about all aspects of Venus’s evolution and how understanding Venus can teach us about other planets, including exoplanets. Here we provide the general background and motivation required to delve into the other manuscripts in this collection. Finally, we discuss how our ignorance about the evolution of Venus motivated the prioritization of new spacecraft missions that will rediscover Earth’s nearest planetary neighbor—beginning a new age of Venus exploration.
 
The Planetary Instrument for X-ray Lithochemistry (PIXL) is a micro-focus X-ray fluorescence spectrometer that is mounted on the robotic arm of NASA’s Perseverance rover. PIXL scans target surfaces with high spacial resolution yielding detailed analyses of rock or soil elemental chemistry. The elemental maps are produced by a narrow 120 μm X-ray beam. These scans are correlated to images captured by PIXL’s Micro Context Camera (MCC) which tie the X-ray measurements to the visual texture and structure of the sample, revealing the distribution and variations of chemical elements within the rock. The PIXL subsystem that determines this correspondence is the Optical Fiducial System (OFS), which is comprised of the MCC, two Structured Light Illuminators (SLI) and a Floodlight Illuminator (FLI). This paper discusses the pre-flight calibration of the OFS, including optical calibration of the MCC, radiometric calibration of the floodlight system and geometric calibration of the structured light illumination beam together with an overall geometric calibration of the OFS and the X-ray beam. Finally, results from the performance verification are presented.
 
The Orbiting Astronomical Satellite for Investigating Stellar Systems (OASIS), a proposed Astrophysics MIDEX-class mission concept, has an innovative 14-meter diameter inflatable primary mirror that will provide the sensitivity to study far-infrared continuum and line emission from galaxies at all redshifts with high spectral resolution heterodyne receivers. OASIS will have the sensitivity to follow the water trail from galaxies to the comets that create oceans. It will bring an understanding of the role of water in galaxy evolution and its part of the oxygen budget, by measuring water emission from local to intermediate redshift galaxies, observations that have not been possible from the ground. Observation of the ground-state HD line will accurately measure gas mass in a wide variety of astrophysical objects. Thanks to its exquisite spatial resolution and sensitivity, OASIS will, during its one-year baseline mission, detect water in galaxies with unprecedented statistical significance. This paper reviews the extragalactic science achievable and planned with OASIS.
 
Launched on 12 Aug. 2018, NASA’s Parker Solar Probe had completed 13 of its scheduled 24 orbits around the Sun by Nov. 2022. The mission’s primary science goal is to determine the structure and dynamics of the Sun’s coronal magnetic field, understand how the solar corona and wind are heated and accelerated, and determine what processes accelerate energetic particles. Parker Solar Probe returned a treasure trove of science data that far exceeded quality, significance, and quantity expectations, leading to a significant number of discoveries reported in nearly 700 peer-reviewed publications. The first four years of the 7-year primary mission duration have been mostly during solar minimum conditions with few major solar events. Starting with orbit 8 (i.e., 28 Apr. 2021), Parker flew through the magnetically dominated corona, i.e., sub-Alfvénic solar wind, which is one of the mission’s primary objectives. In this paper, we present an overview of the scientific advances made mainly during the first four years of the Parker Solar Probe mission, which go well beyond the three science objectives that are: (1) Trace the flow of energy that heats and accelerates the solar corona and solar wind; (2) Determine the structure and dynamics of the plasma and magnetic fields at the sources of the solar wind; and (3) Explore mechanisms that accelerate and transport energetic particles.
 
Herbig Ae/Be stars are young contracting stars on the radiative track in the HR diagram on their way to the main sequence. These stars provide a valuable link between high and low mass stars. Here we review the progress that has been made in our understanding of these fascinating objects and their disks since the last major review on this topic published in 1998. We begin with a general overview of these stars and their properties. We then discuss the accretion of circumstellar material onto these stars. Next we discuss the dust and gas properties of the circumstellar disk before exploring the evidence for planet formation in these disks. We conclude with a brief discussion of future prospects for deepening our understanding of these sources and propose a new working definition of Herbig Ae/Be stars.
 
The “Mars Microphone” is one of the five measurement techniques of SuperCam, an improved version of the ChemCam instrument that has been functioning aboard the Curiosity rover for several years. SuperCam is located on the rover’s Mast Unit, to take advantage of the unique pointing capabilities of the rover’s head. In addition to being the first instrument to record sounds on Mars, the SuperCam Microphone can address several original scientific objectives: the study of sound associated with laser impacts on Martian rocks to better understand their mechanical properties, the improvement of our knowledge of atmospheric phenomena at the surface of Mars such as atmospheric turbulence, convective vortices, dust lifting processes and wind interactions with the rover itself. The microphone also helps our understanding of the sound signature of the different movements of the rover: operations of the robotic arm and the mast, driving on the rough surface of Mars, monitoring of the pumps, etc. The SuperCam Microphone was delivered to the SuperCam team in early 2019 and integrated at the Jet Propulsion Laboratory (JPL), Pasadena, CA with the complete SuperCam instrument. The Mars 2020 Mission launched in July 2020 and landed on Mars on February 18, 2021. The mission operations are expected to last until at least August 2023. The microphone is operating perfectly.
 
Gas-surface interactions at the Moon, Mercury and other massive planetary bodies constitute, alongside production and escape, an essential element of the physics of their gravitationally bound exospheres. From condensation and accumulation of exospheric species onto the surface in response to diurnal and seasonal changes of surface temperature, to thermal accommodation, diffusion and ultimate escape of these species from the regolith back into space, surface-interactions have a drastic impact on exospheric composition, structure and dynamics. The study of this interaction at planetary bodies combines exospheric modeling and observations with a consideration of fundamental physics and laboratory experimentation in surface science. With a growing body of earth-based and spacecraft observational data, and a renewed focus on lunar missions and exploration, the connection between the exospheres and surfaces of planetary bodies is an area of active and growing research, with advances being made on problems such as topographical and epiregolith thermal effects on volatile cold trapping, among others. In this paper we review current understanding, latest developments, outstanding issues and future directions on the topic of exosphere-surface interactions at the Moon, Mercury and elsewhere.
 
Top: Relative VER for one daytime orbit on 1 January 2020. Bottom: Zonal winds corresponding to the VER plot. Each plot is over 90–160 km and the UT, latitude, and longitude are given. See text for details on VER units
Top: Residual of the relative volume emission rate for the same daytime orbit as Fig. 1 with locations of peaks found by the algorithm described in Sect. 2 as black dots. Bottom: Residual of the zonal winds for the same daytime orbit as Fig. 1 with locations of peaks found by the algorithm described in Sect. 2 as black dots
a: A histogram of the slopes found for all events from the relative VER data. b: A histogram of the slopes found for all events from the zonal wind data. c: A histogram of the slopes found for all events from temperature data. All three are bimodal with two peaks close to ±0.01km/km\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\pm0.01~\text{km/km}$\end{document}. Bins are 0.002 km/km in size. See text for explanation of units
a: the latitude distribution of events found in 2020 in relative volume emission rate. b: the latitude distribution of events found in 2020 in zonal winds. c: the latitude distribution of events found in 2020 in temperature. d: the same as a) but number has been normalized to the total number of MIGHTI samples in that latitude bin. e: the same as b) but number has been normalized to the total number of MIGHTI samples in that latitude bin. f: the same as c) but number has been normalized to the total number of MIGHTI samples in that latitude bin. Bins are 1∘\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$1{^{\circ}}$\end{document} latitude in size. The reader is cautioned in interpreting these data. See text for details
a: the longitude distribution of occurrences found in 2020 from the relative volume emission rate data. b: the longitude distribution of occurrences found in 2020 from the zonal wind data. c: the longitude distribution of occurrences found in 2020 from the temperature data. d: the same as a) but number has been normalized to the total number of MIGHTI samples in that longitude bin. e: the same as b) but number has been normalized to the total number of MIGHTI samples in that longitude bin. f: the same as c) but number has been normalized to the total number of MIGHTI samples in that longitude bin. All three distributions show local peaks around 90∘\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$90{^{\circ}}$\end{document} East and 180∘\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$180{^{\circ}}$\end{document} East. The lack of data inside the SAA is also visible in all three distributions. Bins are is 15∘\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$15{^{ \circ}}$\end{document} longitude in size
The Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) onboard the NASA Ionospheric Connection Explorer (ICON) has retrieved profiles of thermospheric wind and temperature in the 90–300 km range for over two years. As part of these limb-viewing measurements, MIGHTI also retrieves a relative volume emission rate (VER) of two atomic oxygen (OI) emissions in the same altitude range. Generally, the VER data do not vary in concert with the retrieved winds or temperatures. However, there are periods of observations where the VER measurements clearly vary together with the wind and temperature measurements, in unexpectedly prominent, large-scale structures. These large-scale variations are smaller than the tidal structures that are investigated as part of ICON’s main mission. In this study, we present these large-scale variations as they appear together in the MIGHTI VER, zonal wind, and temperature products. We present a method to extract wave parameters from these structures and show their properties over the entire year of 2020. These large-scale waves consistently have vertical-to-horizontal slopes of 0.01 km/km, an upper-limit of ∼3000km for horizontal wavelengths and of ∼35km for vertical wavelengths. We interpret these waves as inertia gravity waves. While observational evidence for such waves is not new, it was not expected to observe their signatures with ICON data. Thus, this new global data set opens up a new and unique data source to explore this wave-type.
 
Vortex flows, related to solar convective turbulent dynamics at granular scales and their interplay with magnetic fields within intergranular lanes, occur abundantly on the solar surface and in the atmosphere above. Their presence is revealed in high-resolution and high-cadence solar observations from the ground and from space and with state-of-the-art magnetoconvection simulations. Vortical flows exhibit complex characteristics and dynamics, excite a wide range of different waves, and couple different layers of the solar atmosphere, which facilitates the channeling and transfer of mass, momentum and energy from the solar surface up to the low corona. Here we provide a comprehensive review of documented research and new developments in theory, observations, and modelling of vortices over the past couple of decades after their observational discovery, including recent observations in $\text{H}\alpha $ H α , innovative detection techniques, diverse hydrostatic modelling of waves and forefront magnetohydrodynamic simulations incorporating effects of a non-ideal plasma. It is the first systematic overview of solar vortex flows at granular scales, a field with a plethora of names for phenomena that exhibit similarities and differences and often interconnect and rely on the same physics. With the advent of the 4-m Daniel K. Inouye Solar Telescope and the forthcoming European Solar Telescope, the ongoing Solar Orbiter mission, and the development of cutting-edge simulations, this review timely addresses the state-of-the-art on vortex flows and outlines both theoretical and observational future research directions.
 
Within the fully integrated magnetosphere-ionosphere system, many electrodynamic processes interact with each other. We review recent advances in understanding three major meso-scale coupling processes within the system: the transient field-aligned currents (FACs), mid-latitude plasma convection, and auroral particle precipitation. (1) Transient FACs arise due to disturbances from either dayside or nightside magnetosphere. As the interplanetary shocks suddenly compress the dayside magnetosphere, short-lived FACs are induced at high latitudes with their polarity successively changing. Magnetotail dynamics, such as substorm injections, can also disturb the current structures, leading to the formation of substorm current wedges and ring current disruption. (2) The mid-latitude plasma convection is closely associated with electric fields in the system. Recent studies have unraveled some important features and mechanisms of subauroral fast flows. (3) Charged particles, while drifting around the Earth, often experience precipitating loss down to the upper atmosphere, enhancing the auroral conductivity. Recent studies have been devoted to developing more self-consistent geospace circulation models by including a better representation of the auroral conductance. It is expected that including these new advances in geospace circulation models could promisingly strengthen their forecasting capability in space weather applications. The remaining challenges especially in the global modeling of the circulation system are also discussed.
 
Unlabelled: The NASA InSight Lander on Mars includes the Heat Flow and Physical Properties Package HP3 to measure the surface heat flow of the planet. The package uses temperature sensors that would have been brought to the target depth of 3-5 m by a small penetrator, nicknamed the mole. The mole requiring friction on its hull to balance remaining recoil from its hammer mechanism did not penetrate to the targeted depth. Instead, by precessing about a point midway along its hull, it carved a 7 cm deep and 5-6 cm wide pit and reached a depth of initially 31 cm. The root cause of the failure - as was determined through an extensive, almost two years long campaign - was a lack of friction in an unexpectedly thick cohesive duricrust. During the campaign - described in detail in this paper - the mole penetrated further aided by friction applied using the scoop at the end of the robotic Instrument Deployment Arm and by direct support by the latter. The mole tip finally reached a depth of about 37 cm, bringing the mole back-end 1-2 cm below the surface. It reversed its downward motion twice during attempts to provide friction through pressure on the regolith instead of directly with the scoop to the mole hull. The penetration record of the mole was used to infer mechanical soil parameters such as the penetration resistance of the duricrust of 0.3-0.7 MPa and a penetration resistance of a deeper layer ( > 30 cm depth) of 4.9 ± 0.4 MPa . Using the mole's thermal sensors, thermal conductivity and diffusivity were measured. Applying cone penetration theory, the resistance of the duricrust was used to estimate a cohesion of the latter of 2-15 kPa depending on the internal friction angle of the duricrust. Pushing the scoop with its blade into the surface and chopping off a piece of duricrust provided another estimate of the cohesion of 5.8 kPa. The hammerings of the mole were recorded by the seismometer SEIS and the signals were used to derive P-wave and S-wave velocities representative of the topmost tens of cm of the regolith. Together with the density provided by a thermal conductivity and diffusivity measurement using the mole's thermal sensors, the elastic moduli were calculated from the seismic velocities. Using empirical correlations from terrestrial soil studies between the shear modulus and cohesion, the previous cohesion estimates were found to be consistent with the elastic moduli. The combined data were used to derive a model of the regolith that has an about 20 cm thick duricrust underneath a 1 cm thick unconsolidated layer of sand mixed with dust and above another 10 cm of unconsolidated sand. Underneath the latter, a layer more resistant to penetration and possibly containing debris from a small impact crater is inferred. The thermal conductivity increases from 14 mW/m K to 34 mW/m K through the 1 cm sand/dust layer, keeps the latter value in the duricrust and the sand layer underneath and then increases to 64 mW/m K in the sand/gravel layer below. Supplementary information: The online version contains supplementary material available at 10.1007/s11214-022-00941-z.
 
Interstellar dust particles were discovered in situ, in the solar system, with the Ulysses mission’s dust detector in 1992. Ever since, more interstellar dust particles have been measured inside the solar system by various missions, providing insight into not only the composition of such far-away visitors, but also in their dynamics and interaction with the heliosphere. The dynamics of interstellar (and interplanetary) dust in the solar/stellar systems depend on the dust properties and also on the space environment, in particular on the heliospheric/astrospheric plasma, and the embedded time-variable magnetic fields, via Lorentz forces. Also, solar radiation pressure filters out dust particles depending on their composition. Charge exchanges between the dust and the ambient plasma occur, and pick-up ions can be created. The role of the dust for the physics of the heliosphere and astrospheres is fairly unexplored, but an important and a rapidly growing topic of investigation. This review paper gives an overview of dust processes in heliospheric and astrospheric environments, with its resulting dynamics and consequences. It discusses theoretical modeling, and reviews in situ measurements and remote sensing of dust in and near our heliosphere and astrospheres, with the latter being a newly emerging field of science. Finally, it summarizes the open questions in the field.
 
The ESA Swarm mission, launched on 22 November 2013, consists of three spacecraft each equipped with a Micro Advanced Stellar Compass (μASC) from the Technical University of Denmark (DTU). Each μASC features three Camera Head Units (CHUs) orientated orthogonally to optimize system accuracy performance and avoid simultaneous blinding. The image sensors inside the CHUs are sensitive to ionizing radiation. When an energetic particle impacts the image sensor, electrons are liberated along the particle’s ionizing track and appear on the source image as white dots dubbed ‘energetic particle detection’ (EPD) events. For star tracker applications EPDs are normally supressed to support nominal attitude operation. However, in early 2018 software was uploaded to the μASCs on-board Swarm, which on top of using the EPD measurements to improve the image for star tracking, is reporting the EPD count to the telemetry to ground. This added functionality enables detection and monitoring of high energy particles. By taking advantage of the sample rates (1-2 Hz), the orientation of the camera heads and simultaneous measurements from all three spacecraft spatial derivatives of the EDP aligned to electric and magnetic fields can be determined. Furthermore, since the Swarm spacecraft are in circular, near-polar orbits at an altitude of 450-510 km the spacecraft continuously monitor and map high energy particles at the South Atlantic Anomaly (SAA) of relevance for future mission planning as well as provide detailed time-radiation relations from charge injections processes from e.g. Coronal Mass Ejections (CMEs). In this work we present processes and analysis of four years of high energy radiation data obtained from the Micro Advanced Stellar Compass (μASC) on board ESA’s Swarm mission, from February 2018 to February 2022.
 
The dynamics and evolution of Venus’ mantle are of first-order relevance for the origin and modification of the tectonic and volcanic structures we observe on Venus today. Solid-state convection in the mantle induces stresses into the lithosphere and crust that drive deformation leading to tectonic signatures. Thermal coupling of the mantle with the atmosphere and the core leads to a distinct structure with substantial lateral heterogeneity, thermally and compositionally. These processes ultimately shape Venus’ tectonic regime and provide the framework to interpret surface observations made on Venus, such as gravity and topography. Tectonic and convective processes are continuously changing through geological time, largely driven by the long-term thermal and compositional evolution of Venus’ mantle. To date, no consensus has been reached on the geodynamic regime Venus’ mantle is presently in, mostly because observational data remains fragmentary. In contrast to Earth, Venus’ mantle does not support the existence of continuous plate tectonics on its surface. However, the planet’s surface signature substantially deviates from those of tectonically largely inactive bodies, such as Mars, Mercury, or the Moon. This work reviews the current state of knowledge of Venus’ mantle dynamics and evolution through time, focussing on a dynamic system perspective. Available observations to constrain the deep interior are evaluated and their insufficiency to pin down Venus’ evolutionary path is emphasised. Future missions will likely revive the discussion of these open issues and boost our current understanding by filling current data gaps; some promising avenues are discussed in this chapter.
 
The Van Allen Probes Electric Fields and Waves (EFW) instrument provided measurements of electric fields and spacecraft floating potentials over a wide dynamic range from DC to 6.5 kHz near the equatorial plane of the inner magnetosphere between 600 km altitude and 5.8 Re geocentric distance from October 2012 to November 2019. The two identical instruments provided data to investigate the quasi-static and low frequency fields that drive large-scale convection, waves induced by interplanetary shock impacts that result in rapid relativistic particle energization, ultra-low frequency (ULF) MHD waves which can drive radial diffusion, and higher frequency wave fields and time domain structures that provide particle pitch angle scattering and energization. In addition, measurements of the spacecraft potential provided a density estimate in cold plasmas ( $<20~\text{eV}$ < 20 eV ) from 10 to $3000~\text{cm}^{-3}$ 3000 cm − 3 . The EFW instrument provided analog electric field signals to EMFISIS for wave analysis, and it received 3d analog signals from the EMFISIS search coil sensors for inclusion in high time resolution waveform data. The electric fields and potentials were measured by current-biased spherical sensors deployed at the end of four 50 m booms in the spacecraft spin plane (spin period $\sim11~\text{sec}$ ∼ 11 sec ) and a pair of stacer booms with a total tip-tip separation of 15 m along the spin axis. Survey waveform measurements at 16 and/or 32 S/sec (with a nominal uncertainty of 0.3 mV/m over the prime mission) were available continuously while burst waveform captures at up to 16,384 S/sec provided high frequency waveforms. This post-mission paper provides the reader with information useful for accessing, understanding and using EFW data. Selected science results are discussed and used to highlight instrument capabilities. Science quantities, data quality and error sources, and analysis routines are documented.
 
The Ionospheric CONnections (ICON) mission has been continuously operating during the period from January 2020 to December 2021 providing simultaneous measurements of the thermal plasma properties near 600 km altitude and the neutral atmosphere and ionosphere in the altitude range 100 km to 500 km at low and middle latitudes. During this period of extremely low to moderately low solar activity, the evolving properties of the topside ionospheric density, composition, temperature and drift velocity at the satellite location are described using measurements from the Ion Velocity Meter (IVM). In the early months of 2020, the very low solar activity and relatively high abundance of H+ in the total plasma density present a challenge to a robust description of the full local time distribution of the topside ion drifts. However, the quality of measurements of the ionospheric composition and temperature are not impacted by low solar activity conditions and changes in the O+ and H+ concentrations and their effects on the energy balance in the topside can be investigated as solar activity changes. As the relative abundance of O+ increases, the susceptibility of the ion drift determination to the local plasma environment around the spacecraft is reduced and a more robust determination of the ion drift at all local times is possible. From October 2020 onward, the relationships between the topside ionospheric dynamics and the ionospheric density and temperature can be investigated and the relationships between the plasma drifts and the underlying neutral wind drivers can be established.
 
The Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) was launched aboard NASA’s Ionospheric Connection (ICON) Explorer satellite in October 2019 to measure winds and temperatures on the limb in the upper mesosphere and lower thermosphere (MLT). Temperatures are observed using the molecular oxygen atmospheric band near 763 nm from 90–127 km altitude in the daytime and 90–108 km in the nighttime. Here we describe the measurement approach and methodology of the temperature retrieval, including unique on-orbit operations that allow for a better understanding of the instrument response. The MIGHTI measurement approach for temperatures is distinguished by concurrent observations from two different sensors, allowing for two self-consistent temperature products. We compare the MIGHTI temperatures against existing MLT space-borne and ground-based observations. The MIGHTI temperatures are within 7 K of these observations on average from 90–95 km throughout the day and night. In the daytime on average from 99–105 km, MIGHTI temperatures are higher than coincident observations by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on NASA’s TIMED satellite by 18 K. Because the difference between the MIGHTI and SABER observations is predominantly a constant bias at a given altitude, conclusions of scientific analyses that are based on temperature variations are largely unaffected.
 
The Van Allen Probes mission operations materialized through a distributed model in which operational responsibility was divided between the Mission Operations Center (MOC) and separate instrument specific SOCs. The sole MOC handled all aspects of telemetering and receiving tasks as well as certain scientifically relevant ancillary tasks. Each instrument science team developed individual instrument specific SOCs proficient in unique capabilities in support of science data acquisition, data processing, instrument performance, and tools for the instrument team scientists. In parallel activities, project scientists took on the task of providing a significant modeling tool base usable by the instrument science teams and the larger scientific community. With a mission as complex as Van Allen Probes, scientific inquiry occurred due to constant and significant collaboration between the SOCs and in concert with the project science team. Planned cross-instrument coordinated observations resulted in critical discoveries during the seven-year mission. Instrument cross-calibration activities elucidated a more seamless set of data products. Specific topics include post-launch changes and enhancements to the SOCs, discussion of coordination activities between the SOCs, SOC specific analysis software, modeling software provided by the Van Allen Probes project, and a section on lessons learned. One of the most significant lessons learned was the importance of the original decision to implement individual team SOCs providing timely and well-documented instrument data for the NASA Van Allen Probes Mission scientists and the larger magnetospheric and radiation belt scientific community.
 
There has been scientific debate about speculations that ‘neutrino-induced’ radioactive decay causes apparent violations of the exponential-decay law. Sturrock and others repeatedly publish papers asserting influences by solar and cosmic neutrinos on radioactive decay measurements and therefrom draw conclusions about space science that are highly speculative. Recurrent themes in their work are claims that the solar neutrino flux reveals oscillations at a monthly rate which can be linked to solar rotation, that annual and monthly oscillations occur in radioactive decay rates or directionality of emitted radiation which can be linked to variations in solar and cosmic neutrino flux hitting Earth’s surface, and that unstable radioactivity measurements can be used as a source of information about the interior of the Sun and dark matter. Radionuclide metrologists have extensively investigated and refuted their arguments. Metrological evidence shows that radioactive decay does not violate the exponential-decay law and is not a probe for variations in solar neutrino flux. In this review paper, the main arguments of Sturrock are listed and counterarguments are presented. Reference is made to earlier published work in which the evidence has been scrutinised in detail.
 
The environment of a comet is a fascinating and unique laboratory to study plasma processes and the formation of structures such as shocks and discontinuities from electron scales to ion scales and above. The European Space Agency’s Rosetta mission collected data for more than two years, from the rendezvous with comet 67P/Churyumov-Gerasimenko in August 2014 until the final touch-down of the spacecraft end of September 2016. This escort phase spanned a large arc of the comet’s orbit around the Sun, including its perihelion and corresponding to heliocentric distances between 3.8 AU and 1.24 AU. The length of the active mission together with this span in heliocentric and cometocentric distances make the Rosetta data set unique and much richer than sets obtained with previous cometary probes. Here, we review the results from the Rosetta mission that pertain to the plasma environment. We detail all known sources and losses of the plasma and typical processes within it. The findings from in-situ plasma measurements are complemented by remote observations of emissions from the plasma. Overviews of the methods and instruments used in the study are given as well as a short review of the Rosetta mission. The long duration of the Rosetta mission provides the opportunity to better understand how the importance of these processes changes depending on parameters like the outgassing rate and the solar wind conditions. We discuss how the shape and existence of large scale structures depend on these parameters and how the plasma within different regions of the plasma environment can be characterised. We end with a non-exhaustive list of still open questions, as well as suggestions on how to answer them in the future.
 
The NASA Ionospheric Connection Explorer Extreme Ultraviolet spectrograph, ICON EUV, images one-dimensional altitude profiles of the daytime extreme-ultraviolet (EUV) airglow between 54-88 nm. This spectral range contains several OII emission features derived from the photoionization of atomic oxygen by solar EUV. The primary target of the ICON EUV is the bright OII (4P – 4S) triplet emission spanning 83.2-83.4 nm that is used in combination with a dimmer but complementary feature (2P – 2D) spanning 61.6-61.7 nm that are jointly analyzed with an algorithm that uses discrete inverse theory to optimize a forward model of these emissions to infer the best-fit solution of ionospheric O+ density profile between 150-450 km. From this result, the daytime ionospheric F-region peak electron density and height, NmF2 and hmF2 respectively, are inferred. The science goals of ICON require these measurements be made in the regions of interest with a vertical resolution in hmF2 of 20 km and a 20% precision in NmF2 within a 60-second integration corresponding to a 500 km sampling along the orbit track. This paper describes the results from the ICON EUV over the first year of the mission, which occurred primarily under solar minimum conditions. It describes adjustments made to the algorithm to improve not only the quality of data products during this time, but also to improve speed and performance while simultaneously meeting the ICON measurement requirements. It also provides examples of results and an overview of key features and limitations to consider when using these products for scientific studies.
 
We provide the first comparison of the ICON-EUV O⁺ density profile with radio wave datasets coming from GNSS radio-occultation, ionosondes and incoherent scatter radar. The peak density and height deduced from those different observation techniques are compared. It is found that the EUV-deduced peak density is smaller than that from other techniques by 50 to 60%, while the altitude of the peak is retrieved with a slight bias of 10 to 20 km on average. These average values are found to vary between November 2019 and March 2021. Magnetic latitude and local time are not factors significantly influencing this variability. In contrast, the EUV density is closer to that deduced from radio-wave techniques in the mid latitude region, i.e. where the ionospheric crests do not play a role. The persistent very low solar activity conditions prevailing during the studied time interval challenge the EUV O⁺ density profile retrieval technique. These values are consistent, both in magnitude and direction, with a systematic error on the order of 10% in the data or the forward model, or a combination of both. Ultimately, the EUV instrument on-board ICON provides the only known technique capable of precisely monitoring the ionospheric peak properties at daytime from a single space platform, on a global scale and at high cadence. This feature paves the way to transpose the technology to the study of the ionosphere surrounding other planets.
 
One of the objectives of the Far UltraViolet (FUV) imager on the Ionospheric Connection Explorer (ICON) spacecraft is to make high resolution images of the nighttime near equatorial oxygen 135.6 nm airglow emission. This emission is largely the product of O⁺ ion re-combination and therefore the emission intensity is a proxy for remote measurement of ionospheric density. The ICON FUV instrument is capable of high resolution imaging of the night glow by viewing the Earth’s limb from above on the left side of the spacecraft and taking rapid exposures and co-adding the resultant images for 12 seconds. To improve the resolution and compress the resulting data a new type of Time Delay Integration (TDI) technique was developed, which involves transforming the images into a distorted frame so that the displacement due to orbital motion becomes a singular constant vector for all pixels. Operating in this transformed frame it is possible to co-add and shift the images to retain the resolution and minimize the required data bandwidth. The transformation needs modeling of the object distance for all pixels. Two models, the “limb” and “sub-limb” models, are used for transforming the upper and lower parts of the ICON FUV images, respectively. At the input of the instrument there is a rotatable mirror, which allows directing the optic axis near to the plane of the local magnetic field. The images are co-added for 12 sec and are down linked and re-assembled on the ground into maps of the O emission showing an entire night pass. This is the first report on the performance of this newly developed TDI system. ICON with its low inclination (27 degree) orbit provides an extensive longitudinal coverage on each orbit complementing the coverage of GOLD or TIMED. During 179 orbits in October 2021 ICON FUV saw significant nighttime ion densities on 76% of the orbits. At low latitudes the ionization was clearly associated with the equatorial ionospheric anomaly (EIA). The maps showed significant structuring during 34% of the orbits when ICON was in the position to view the EIA. In coordinated observations GOLD and ICON FUV observed regular structuring in the form of Equatorial Plasma Bubbles (EPB-s). Comparing to GOLD observations in 2018, ICON saw significantly fewer EPB-s in the month of October 2021. ICON TDI integrated sub-limb view was tested for resolution using star images and should have seen structures less than 10 km. From the 179 orbits taken in October 2021 the shortest repetition EPB-were 350 km from peak to peaks.
 
The composition the atmosphere of Venus results from the integration of many processes entering into play over the entire geological history of the planet. Determining the elemental abundances and isotopic ratios of noble gases (He, Ne, Ar, Kr, Xe) and stable isotopes (H, C, N, O, S) in the Venus atmosphere is a high priority scientific target since it could open a window on the origin and early evolution of the entire planet. This chapter provides an overview of the existing dataset on noble gases and stable isotopes in the Venus atmosphere. The current state of knowledge on the origin and early and long-term evolution of the Venus atmosphere deduced from this dataset is summarized. A list of persistent and new unsolved scientific questions stemming from recent studies of planetary atmospheres (Venus, Earth and Mars) are described. Important mission requirements pertaining to the measurement of volatile elements in the atmosphere of Venus as well as potential technical difficulties are outlined.
 
Sampling soil or rocks from extraterrestrial celestial bodies is the essential step to detecting the existence of water and life in celestial bodies, it is also an important channel to obtain scientific information about the evolution of the solar system and the origin of the universe. To date, a large number of sampling devices have been designed and developed for sampling exploration of extraterrestrial celestial bodies. However, the sampling devices are versatile, and the employed working principle and sampling methods vary in different exploration missions and celestial bodies’ environments. The present work focuses on the exploration history, celestial bodies’ environment, and sampling devices of extraterrestrial celestial bodies (mainly the Moon, Mars, and small celestial bodies), and provides a systematic review. First, the exploration history and future exploration plans of extraterrestrial celestial bodies are reviewed, which outlines the features of the exploration methods and sampling devices. In the overview of the exploration history, it is found that the failure of sampling exploration is mainly due to the unknown of the celestial bodies’ environment. Therefore, the surface environment and geology of extraterrestrial celestial bodies are further summarized, and whereby the influence of the environment on sampling device design and performance in the exploration process is analyzed. Then a focused analysis of the sampling devices that have been used in previous exploration missions and recent advances has been conducted, which provides a comprehensive description of their exploration goals, operating principles, and properties. This work summarizes the current sampling methods into nine types: excavating, drilling, grinding, grabbing, projecting, penetrating, wire-line coring, ultrasonic-assisted coring, and pneumatic, for which their advantages, disadvantages, and scope of application are analyzed. Finally, the limitations and challenges faced by extraterrestrial bodies’ sampling exploration are discussed, with prospects for future sampling exploration techniques, which can provide a reference for the subsequent in-depth development of extraterrestrial celestial bodies’ sampling devices.
 
Schematic depicting the progressive lowering of science mapping orbits, designed based on experience with the Dawn mission. Gravity science is prioritized in Orbit C
Shape of Psyche (Shepard et al. 2021) shown from different viewing angles
Block diagram of the Psyche telecommunication system
Schematics showing key components of the Psyche telecommunication system
Gravitational power spectra for an assumed Kaula rule (black-dashed) and for the Shepard et al. (2021) Psyche shape model (blue solid; cf. Fig. 2) assuming a constant density interior. The reference radius of Psyche was assumed to be 113 km. The power spectrum of the expected accuracy of the recovered gravity field from Orbit C is shown in the dashed-blue line. Expected accuracy is defined by the degree at which the formal error spectrum intersects the power spectrum
The objective of the NASA Psyche mission gravity science investigation is to map the mass distribution within asteroid (16) Psyche to elucidate interior structure and to resolve the question of whether this metal-rich asteroid represents a remnant metal core or whether it is a primordial body that never melted. Measurements of gravity will be obtained via the X-band telecommunication system on the Psyche spacecraft, collected from progressively lower mapping altitudes. Orbital gravity will allow an estimate of GM\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$GM$\end{document} to better than 0.001 km³ s⁻². A spherical harmonic model of gravity to degree and order 10 will be achievable and, in concert with spherical harmonic data sets from topography and magnetometry, as well as surface composition data, will provide information regarding the spatial and radial distribution of mass that will be used to constrain the origin and evolution of (16) Psyche.
 
This work reviews the long-term evolution of the atmosphere of Venus, and modulation of its composition by interior/exterior cycling. The formation and evolution of Venus’s atmosphere, leading to contemporary surface conditions, remain hotly debated topics, and involve questions that tie into many disciplines. We explore these various inter-related mechanisms which shaped the evolution of the atmosphere, starting with the volatile sources and sinks. Going from the deep interior to the top of the atmosphere, we describe volcanic outgassing, surface-atmosphere interactions, and atmosphere escape. Furthermore, we address more complex aspects of the history of Venus, including the role of Late Accretion impacts, how magnetic field generation is tied into long-term evolution, and the implications of geochemical and geodynamical feedback cycles for atmospheric evolution. We highlight plausible end-member evolutionary pathways that Venus could have followed, from accretion to its present-day state, based on modeling and observations. In a first scenario, the planet was desiccated by atmospheric escape during the magma ocean phase. In a second scenario, Venus could have harbored surface liquid water for long periods of time, until its temperate climate was destabilized and it entered a runaway greenhouse phase. In a third scenario, Venus’s inefficient outgassing could have kept water inside the planet, where hydrogen was trapped in the core and the mantle was oxidized. We discuss existing evidence and future observations/missions required to refine our understanding of the planet’s history and of the complex feedback cycles between the interior, surface, and atmosphere that have been operating in the past, present or future of Venus.
 
It is now well established that waves generated in the lower atmosphere can propagate upward and significantly impact the dynamics and mean state of the ionosphere-thermosphere (IT, 100-600 km) system. Given the geometry of magnetic field lines near the equator, a significant fraction of this IT coupling occurs at low latitudes (<30∘\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$<30^{\circ}$\end{document}) and is driven by global-scale waves of tropical tropospheric origin, such as the diurnal eastward-propagating tide with zonal wavenumber 3 (DE3) and the ultra-fast Kelvin wave (UFKW). Despite recent progress, lack of coincident global observations has thus far precluded full characterization of the sources of day-to-day variability of these waves, including nonlinear interactions, and impacts on the low-latitude IT. In this work, in-situ ion densities from Ionospheric Connection Explorer (ICON)’s and Constellation Observing System for Meteorology, Ionosphere and Climate 2 (COSMIC-2)’s Ion Velocity Meter (IVM) along with remotely-sensed zonal winds from ICON’s Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) are used to reveal a rich spectrum of waves coupling the lower (∼90-105 km) and middle (∼200-270 km) thermosphere with the upper F-region (∼540 and ∼590 km) ionosphere. Spectral analyses for a 40-day period of similar local time demonstrate prominent IT coupling via DE3, a 3-day UFKW, and the two ∼1.43-day and ∼0.77-day secondary waves from their nonlinear interactions. While all these waves are found to dominate the F-region spectra, only the UFKW and the 1.43-day secondary wave can propagate to ∼270 km suggesting E-region wind dynamo processes as major contributors to their observed ionospheric signatures.
 
The BepiColombo Environment Radiation Monitor (BERM) on board the European Space Agency’s Mercury Planetary Orbiter (MPO), is designed to measure the radiation environment encountered by BepiColombo. The instrument measures electrons with energies from ∼150keV to ∼10MeV, protons with energies from ∼1.5MeV to ∼100MeV, and heavy ions with Linear Energy Transfer from 1 to 50MeV⋅mg−1⋅cm2. BERM is operated continuously, being responsible for monitoring the radiation levels during all phases of the mission, including the cruise, the planetary flybys of Earth, Venus and Mercury, and the Hermean environment. In this paper, we describe the scientific objectives, instrument design and calibration, and the in-flight scientific performance of BERM. Moreover, we provide the first scientific results obtained by BERM during the BepiColombo flyby of Earth in April 2020, and after the impact of a solar energetic particle event during the cruise phase in May 2021. We also discuss the future plans of the instrument including synergies with other instruments on the BepiColombo and on other missions.
 
We present a review of the observations of the solar F-corona from space with a special emphasis of the 25 years of continuous monitoring achieved by the LASCO-C2 and C3 coronagraphs. Our work includes images obtained by the navigation cameras of the Clementine spacecraft, the SECCHI/HI-1A heliospheric imager onboard STEREO-A, and the Wide Field Imager for Solar Probe onboard the Parker Solar Probe. The connection to the zodiacal light is considered based on ground- and space-based observations, prominently from the past Helios, IRAS, COBE, and IRAKI missions. The characteristic radiance profiles along the two symmetry axis of the “elliptically” shaped F-corona (aka equatorial and polar directions) follow power laws in the 5∘\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$5^{\circ }$\end{document}–50∘\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$50^{\circ }$\end{document} range of elongation, with constant power exponents of −2.33 and −2.55. Both profiles connect extremely well to the corresponding standard profiles of the zodiacal light. The LASCO equatorial profile exhibits a shoulder implying a ≈17%\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\approx17\%$\end{document} decrease of the radiance within ≈10R⊙\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\approx10~\text{R}_{\odot }$\end{document} that may be explained by the disappearance of organic materials within 0.3 AU. LASCO detected for the first time a secular variation of the F-corona, an increase at a rate of 0.46% per year of the integrated radiance in the LASCO-C3 field of view. This is likely the first observational evidence of the role of collisions in the inner zodiacal cloud. The temporal evolution of the integrated radiance in the LASCO-C2 field of view is more complex suggesting possible additional processes. Whereas it is well established that the F-corona is slightly redder than the Sun, the spectral variation of its color index is not yet well established. A composite of C2 and C3 images produced the LASCO reference map of the radiance of the F-corona from 2 to 30R⊙\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$30~\text{R}_{\odot }$\end{document} and, by combining with ground-based measurements, the LASCO extended map from 1 to 6R⊙\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$6~\text{R}_{\odot }$\end{document}. An upper limit of 0.03R⊙\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$0.03~\text{R}_{\odot}$\end{document} is obtained for the offset between the center of the Sun and that of the F-corona with a most likely value of zero. The flattening index of the F-corona starts from zero at an elongation of 0.5∘±0.01∘\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$0.5^{\circ }\pm0.01^{\circ }$\end{document} (1.9R⊙\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$1.9~\text{R}_{ \odot }$\end{document}) and increases linearly with the logarithm of the elongation to connect to that of the zodiacal light with however a small hump related to the shoulder in the equatorial profile. The shape of the isophotes is best described by super-ellipses with an exponent linked to the flattening index. An ellipsoid model of the spatial density of interplanetary dust is solely capable of reproducing this shape, thus rejecting other classical models such as fan, and cosine. The plane of symmetry of the inner zodiacal cloud is strongly warped, its inclination increasing towards the planes of the inner planets and ultimately the solar equator. In contrast, its longitude of ascending node is found to be constant and equal to 87.6∘\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$87.6^{ \circ }$\end{document}. LASCO did not detect any small scale structures such as putative rings occasionally reported during solar eclipses. The outer border of the depletion zone where interplanetary dust particles start to be affected by sublimation appears well constrained at ≈19R⊙\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\approx19~\text{R}_{\odot }$\end{document}. This zone extends down to ≈5R⊙\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\approx5~\text{R}_{\odot}$\end{document}, thus defining the boundary of the dust-free zone where the most refractory materials – likely moderately absorbing silicates – disappear.
 
Swarm is the first European Space Agency (ESA) constellation mission for Earth Observation. Three identical Swarm satellites were launched into near-polar orbits on 22 November 2013. Each satellite hosts a range of instruments, including a Langmuir probe, GPS receivers, and magnetometers, from which the ionospheric plasma can be sampled and current systems inferred. In March 2018, the CASSIOPE/e-POP mission was formally integrated into the Swarm mission through ESA’s Earthnet Third Party Mission Programme. Collectively the instruments on the Swarm satellites enable detailed studies of ionospheric plasma, together with the variability of this plasma in space and in time. This allows the driving processes to be determined and understood. The purpose of this paper is to review ionospheric results from the first seven years of the Swarm mission and to discuss scientific challenges for future work in this field.
 
One of the earliest indicators of the importance of shock acceleration of solar energetic particles (SEPs) was the broad spatial extent of the "gradual" SEP events produced as the shock waves, driven by wide, fast coronal mass ejections (CMEs), expand across the Sun with cross-field transport mediated by the shocks. Contrasting "impulsive" SEP events, with characteristic enhancements of 3 He and of heavy elements, are now associated with magnetic reconnection on open field lines in solar jets. However, large shock waves can also traverse pools of residual impulsive suprathermal ions and jets can produce fast CMEs that drive shock waves; in both cases shocks reaccelerate ions with the "impulsive" abundance signatures as well as coronal plasma. These more-complex events produce "excess protons" that identify this process, and recently, differences in the distribution of 4He abundances have also been found to depend upon the combination of seed population and acceleration mode. Extreme differences in the 4He abundances may reflect underlying differences in the abundances of the coronal regions being sampled by solar jets and, surprisingly, SEP events where shock waves sample two seed-particle populations seem to have about twice the 4He/O ratio of those with a single source.
 
This paper presents a review of the space exploration for life signature search with a special focus on the fluorescence microscope we developed for the life signature search on Mars and in other sites. Considering where, what, and how to search for life signature is essential. Life signature search exploration can be performed on the Mars surface and underground, on Venus’ cloud, moon, asteroids, icy bodies (e.g., moons of Jupiter and Saturn), and so on. It is a useful strategy to consider the targeted characteristics that may be similar to those of terrestrial microorganisms, which are microorganisms with uniform spherical or rod structures with approximately 1 μm diameter surrounded by a membrane having a metabolic activity and mainly made of carbon-based molecules. These characteristics can be analyzed by using a fluorescence microscope and a combination of fluorescence pigments with specific staining characteristics to distinguish the microorganism characteristics. Section 1 introduces the space exploration for life signature search. Section 2 reviews the scientific instruments and achievements of past and ongoing Mars exploration missions closely related to astrobiology. Section 3 presents the search targets and analysis of astrobiology. Section 4 discusses the extraterrestrial life exploration methods that use a microscope together with other methods (based on mass spectrometry, morphology, detection of growth, movement, and death, etc. for microscopic and macroscopic organism). Section 5 expounds on the life signature detection fluorescence microscope, for which we have manufactured a bread board model and tested for extraterrestrial life exploration.
 
The solar wind (SW) and local interstellar medium (LISM) are turbulent media. Their interaction is governed by complex physical processes and creates heliospheric regions with significantly different properties in terms of particle populations, bulk flow and turbulence. Our knowledge of the solar wind turbulence nature and dynamics mostly relies on near-Earth and near-Sun observations, and has been increasingly improving in recent years due to the availability of a wealth of space missions, including multi-spacecraft missions. In contrast, the properties of turbulence in the outer heliosphere are still not completely understood. In situ observations by Voyager and New Horizons, and remote neutral atom measurements by IBEX strongly suggest that turbulence is one of the critical processes acting at the heliospheric interface. It is intimately connected to charge exchange processes responsible for the production of suprathermal ions and energetic neutral atoms. This paper reviews the observational evidence of turbulence in the distant SW and in the LISM, advances in modeling efforts, and open challenges.
 
The Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) is a robotic arm-mounted instrument onboard NASA’s Perseverance rover. SHERLOC combines imaging via two cameras with both Raman and fluorescence spectroscopy to investigate geological materials at the rover’s Jezero crater field site. SHERLOC requires in situ calibration to monitor the health and performance of the instrument. These calibration data are critically important to ensure the veracity of data interpretation, especially considering the extreme martian environmental conditions where the instrument operates. The SHERLOC Calibration Target (SCT) is located at the front of the rover and is exposed to the same atmospheric conditions as the instrument. The SCT includes 10 individual targets designed to meet all instrument calibration requirements. An additional calibration target is mounted inside the instrument’s dust cover. The targets include polymers, rock, synthetic material, and optical pattern targets. Their primary function is calibration of parameters within the SHERLOC instrument so that the data can be interpreted correctly. The SCT was also designed to take advantage of opportunities for supplemental science investigations and includes targets intended for public engagement. The exposure of materials to martian atmospheric conditions allows for opportunistic science on extravehicular suit (i.e., “spacesuit”) materials. These samples will be used in an extended study to produce direct measurements of the expected service lifetimes of these materials on the martian surface, thus helping NASA facilitate human exploration of the planet. Other targets include a martian meteorite and the first geocache target to reside on another planet, both of which increase the outreach and potential of the mission to foster interest in, and enthusiasm for, planetary exploration. During the first 200 sols (martian days) of operation on Mars, the SCT has been analyzed three times and has proven to be vital in the calibration of the instrument and in assisting the SHERLOC team with interpretation of in situ data.
 
Deep space exploration can satisfy humanity’s curiosity about the origin of life and the evolution of the universe and enhance our understanding of the internal geological structure and climate change of extraterrestrial bodies. The most direct way to explore extraterrestrial bodies is to sample and analyze the regolith. Drilling is the most effective sampling method, and extraterrestrial regolith drills have helped humans acquire many samples in planetary exploration. Developing high applicable and flexible ERDs for extraterrestrial regolith penetration and sampling has attracted strong attention from scientists and engineers worldwide. This paper presents a detailed review of extraterrestrial drilling technologies. Firstly, the particularities of extraterrestrial drilling are introduced. Then, the ERDs utilized in previous planetary exploration missions and the latest advances are reviewed in detail, including the categories, historical context, and (dis)advantages. Next, the general characteristics of extraterrestrial drilling are summarized, including the mainstream approaches to studying the drilling mechanics and thermophysics. Then, the critical technologies of ERDs, from a conceptual design to a practical prototype, are analyzed in depth. Finally, the prospects for extraterrestrial drilling technology are presented, including water ice drilling, long tunnel boring, deep drilling, and intelligent drilling.
 
The Entry, Descent and Landing Demonstrator Module (EDM) named Schiaparelli, was the ESA-led Mars lander element of the ESA-Roscosmos ExoMars 2016 mission. Following launch on 14 March 2016 with the ExoMars Trace Gas Orbiter (TGO) and cruise to Mars, Schiaparelli separated for encounter with Mars to demonstrate entry, descent and landing technologies. Although on 19 October 2016 the final touchdown and surface operation were not achieved, other aspects were demonstrated and reported via real-time telemetry transmitted at 8 kbps in UHF during entry and descent. This paper presents a technical description of the elements of the Schiaparelli EDM system and its operation, plus reference to published post-flight analyses of the data obtained.
 
The full sky map (in ecliptic J2000 coordinates) of the Lyman-α\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\alpha $\end{document} intensity observed by SWAN/SOHO on 17 March 1996. The white areas represent regions of the sky which can not be observed by SWAN or which are contaminated by hot stars of the Galactic plane. The color represents the intensity in counts per second per pixel (one square degree). Credit: https://sohowww.nascom.nasa.gov/gallery/Particle/swa005.html
(A) Temporal and heliolatitudinal variations of the charge exchange ionization rate derived from SOHO/SWAN data. Panels B and C show averaged latitudinal profiles in particular years of the solar minimum (1996 and 2009) and solar maximum (2003 and 2015) periods, respectively. Adapted from Katushkina et al. (2019)
Modeled interplanetary Lyman-α\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\alpha $\end{document} line profile in the upwind direction. The simulation was performed in the self-absorption approximation for an observer at 1 AU in the upwind direction from the Sun. The Doppler shift velocity in the solar rest frame is presented on the x-axis in km/s. The emission due to the primary H population is shown by the dash-dotted line, the secondary hydrogen by the dashed line, and the hot component by the dotted line. The solid line presents the total emission due to the three hydrogen populations. Adapted from Quémerais and Izmodenov (2002)
The Lyman-α\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\alpha $\end{document} line profile in the upwind direction observed by HST/STIS in March 2001. The dotted line presents the original profile. The geocoronal emission (dashed line) was removed from the data, and the rest is associated with the IP background emission (solid line). The x-axis shows the wavelength in the Earth rest frame in units of Angstrom, so the geocoronal line is centered at 1215.67 Å. Adapted from Quémerais et al. (2009)
Full sky sinusoidal projections (in ecliptic J2000 coordinates) of the Lyman-α\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\alpha $\end{document} intensities Ioff\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$I_{\mathrm{off}}$\end{document} (panel A), Ion\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$I_{\mathrm{on}}$\end{document} (panel B), Ioff−Ion\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$I_{\mathrm{off}} - I_{\mathrm{on}}$\end{document} (panel C), and reduction factor R=Ion/Ioff\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$R = I_{\mathrm{on}} / I_{\mathrm{off}}$\end{document} (panel D) observed by SWAN/SOHO on 26 January 1997. Adapted from Baliukin et al. (2019)
This review summarizes our current understanding of the outer heliosphere and local interstellar medium (LISM) inferred from observations and modeling of interplanetary Lyman- $\alpha $ α emission. The emission is produced by solar Lyman- $\alpha $ α photons (121.567 nm) backscattered by interstellar H atoms inflowing to the heliosphere from the LISM. Studies of Lyman- $\alpha $ α radiation determined the parameters of interstellar hydrogen within a few astronomical units from the Sun. The interstellar hydrogen atoms appeared to be decelerated, heated, and shifted compared to the helium atoms. The detected deceleration and heating proved the existence of secondary hydrogen atoms created near the heliopause. This finding supports the discovery of a Hydrogen Wall beyond the heliosphere consisting of heated hydrogen observed in HST/GHRS Lyman- $\alpha $ α absorption spectra toward nearby stars. The shift of the interstellar hydrogen bulk velocity was the first observational evidence of the global heliosphere asymmetry confirmed later by Voyager in situ measurements. SOHO/SWAN all-sky maps of the backscattered Lyman- $\alpha $ α intensity identified variations of the solar wind mass flux with heliolatitude and time. In particular, two maxima at mid-latitudes were discovered during solar activity maximum, which Ulysses missed due to its specific trajectory. Finally, Voyager/UVS and New Horizons/Alice UV spectrographs discovered extraheliospheric Lyman- $\alpha $ α emission. We review these scientific breakthroughs, outline open science questions, and discuss potential future heliospheric Lyman- $\alpha $ α experiments.
 
The overarching theme of the Orbiting Astronomical Satellite for Investigating Stellar Systems (OASIS) , an Astrophysics MIDEX-class mission concept, is Following water from galaxies, through protostellar systems, to Earth’s oceans . The OASIS science objectives address fundamental questions raised in “Pathways to Discovery in Astronomy and Astrophysics for the 2020s (National Academies of Sciences and Medicine, Pathways to Discovery in Astronomy and Astrophysics for the 2020s, 2021, https://doi.org/10.17226/26141 , https://www.nap.edu/catalog/26141/pathways-to-discovery-in-astronomy-and-astrophysics-for-the-2020s )” and in “Enduring Quests and Daring Visions” (Kouveliotou et al. in Enduring quests-daring visions (NASA astrophysics in the next three decades), 2014, arXiv:1401.3741 ), in the areas of: 1) the Interstellar Medium and Planet Formation, 2) Exoplanets, Astrobiology, and the Solar System, and 3) Galaxies. The OASIS science objectives require space-borne observations of galaxies, molecular clouds, protoplanetary disks, and solar system objects utilizing a telescope with a collecting area that is only achievable by large apertures coupled with cryogenic heterodyne receivers. OASIS will deploy an innovative 14-meter inflatable reflector that enables >16× the sensitivity and >4× the angular resolution of Herschel , and complements the short wavelength capabilities of James Webb Space Telescope . The OASIS state-of-the-art cryogenic heterodyne receivers will enable high spectral resolution (resolving power $>10^{6}$ > 10 6 ) observations at terahertz (THz) frequencies. These frequencies encompass far-IR transitions of water and its isotopologues, HD, and other molecular species, from 660 to 63 μm that are otherwise obscured by Earth’s atmosphere. From observations of the ground state HD line, OASIS will directly measure gas mass in a wide variety of astrophysical objects. Over its one-year baseline mission, OASIS will find water sources as close as the Moon, to galaxies ∼4 billion light years away. This paper reviews the solar system science achievable and planned with OASIS .
 
We review recent observations and modeling developments on the subject of galactic cosmic rays through the heliosphere and in the Very Local Interstellar Medium, emphasizing knowledge that has accumulated over the past decade. We begin by highlighting key measurements of cosmic-ray spectra by Voyager, PAMELA, and AMS and discuss advances in global models of solar modulation. Next, we survey recent works related to large-scale, long-term spatial and temporal variations of cosmic rays in different regimes of the solar wind. Then we highlight new discoveries from beyond the heliopause and link these to the short-term evolution of transients caused by solar activity. Lastly, we visit new results that yield interesting insights from a broader astrophysical perspective.
 
The Lunar Mineralogical Spectrometer (LMS) is one of the main payloads on the Chang’E-5 (CE-5) lunar probe, belonging to the China Lunar Exploration Program. The scientific objective of the LMS is to explore the mineralogical composition and search for evidence of -OH/H 2 O in the sampling area. The LMS consists of an optomechanism unit, a dustproof calibration unit (DPCU) and an electronic unit. The LMS is installed on the lander about 1.4-m above the lunar surface, the field of view (FOV) is $4.17\times 4.17^{\circ }$ 4.17 × 4.17 ∘ , the instant FOV of the visible imaging channel is 0.28 mrad, and the typical spatial resolution is 0.56 mm/pixel @ 2 m distance. The rotation range of the 2D scanner is $\pm 22.5^{\circ}$ ± 22.5 ∘ along the azimuth axis and $0\sim 30^{\circ }$ 0 ∼ 30 ∘ along the elevation axis, making it possible to observe the sampling area or to select important observing targets. The dispersing beam uses acousto-optic tunable filters, and target detection is performed with a 2D scanner. The LMS acquires spectral imaging information covering 480–950 nm, and reflectance spectra of 900–3,200-nm, both at a 5-nm/band sampling interval. The spectral resolution is $2.4\sim 9.4\text{ nm}$ 2.4 ∼ 9.4 nm in the visible and near-infrared channels and $7.6\sim 24.9\text{ nm}$ 7.6 ∼ 24.9 nm in the short–medium-wave infrared channel. The LMS has a 588-band detection capability designed for fine spectral observation of sampling points and wields a 20-band full-view multi-spectral mode to observe candidate areas prior to sampling. The DPCU of the LMS is integrated with a calibration diffuser that is used for in-flight calibration on the lunar surface using solar irradiation, thus improving the quantitative level of scientific data.
 
NASA’s Endurance sounding rocket (yard No. 47.001) will launch from Ny Ålesund, Svalbard in May 2022 on a solid fueled Oriole III-A launch vehicle. Its ∼19\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\sim19$\end{document} minute flight will carry it to an altitude of ∼780km\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\sim780~\text{km}$\end{document} above Earth’s sunlit polar cap. Its objective is to make the first measurement of the weak “ambipolar” electric field generated by Earth’s ionosphere. This field is thought to play a critical role in the upwelling and escape of ionospheric ions, and thus potentially in the evolution of Earth’s atmosphere. The results will enable us to determine the importance to ion escape of this previously unmeasured fundamental property of our planet, which will aid in a better understanding of what makes Earth habitable. Endurance will carry six science instruments (with 16 sensors) that will measure the total electrical potential drop below the spacecraft, and the physical parameters required to understand the physics of what generates the ambipolar field. The mission will be supported by simultaneous observations of solar and geomagnetic activity.
 
This paper presents the highlights of joint observations of the inner magnetosphere by the Arase spacecraft, the Van Allen Probes spacecraft, and ground-based experiments integrated into spacecraft programs. The concurrent operation of the two missions in 2017–2019 facilitated the separation of the spatial and temporal structures of dynamic phenomena occurring in the inner magnetosphere. Because the orbital inclination angle of Arase is larger than that of Van Allen Probes, Arase collected observations at higher $L$ L -shells up to $L \sim 10$ L ∼ 10 . After March 2017, similar variations in plasma and waves were detected by Van Allen Probes and Arase. We describe plasma wave observations at longitudinally separated locations in space and geomagnetically-conjugate locations in space and on the ground. The results of instrument intercalibrations between the two missions are also presented. Arase continued its normal operation after the scientific operation of Van Allen Probes completed in October 2019. The combined Van Allen Probes (2012-2019) and Arase (2017-present) observations will cover a full solar cycle. This will be the first comprehensive long-term observation of the inner magnetosphere and radiation belts.
 
Dayside transients, such as hot flow anomalies, foreshock bubbles, magnetosheath jets, flux transfer events, and surface waves, are frequently observed upstream from the bow shock, in the magnetosheath, and at the magnetopause. They play a significant role in the solar wind-magnetosphere-ionosphere coupling. Foreshock transient phenomena, associated with variations in the solar wind dynamic pressure, deform the magnetopause, and in turn generates field-aligned currents (FACs) connected to the auroral ionosphere. Solar wind dynamic pressure variations and transient phenomena at the dayside magnetopause drive magnetospheric ultra low frequency (ULF) waves, which can play an important role in the dynamics of Earth’s radiation belts. These transient phenomena and their geoeffects have been investigated using coordinated in-situ spacecraft observations, spacecraft-borne imagers, ground-based observations, and numerical simulations. Cluster, THEMIS, Geotail, and MMS multi-mission observations allow us to track the motion and time evolution of transient phenomena at different spatial and temporal scales in detail, whereas ground-based experiments can observe the ionospheric projections of transient magnetopause phenomena such as waves on the magnetopause driven by hot flow anomalies or flux transfer events produced by bursty reconnection across their full longitudinal and latitudinal extent. Magnetohydrodynamics (MHD), hybrid, and particle-in-cell (PIC) simulations are powerful tools to simulate the dayside transient phenomena. This paper provides a comprehensive review of the present understanding of dayside transient phenomena at Earth and other planets, their geoeffects, and outstanding questions.
 
The ionospheric equivalent slab thickness (τ) is a parameter characterizing both the distribution of the plasma in the ionosphere and the shape of the corresponding vertical electron density profile. It is calculated as the ratio of the vertical total electron content (vTEC) to the ionospheric F2-layer electron density maximum (NmF2). Since its definition dated back in the 60s, a lot of information on the behavior of τ for different helio-geophysical conditions has been cumulated and the connection with several plasma properties has been also demonstrated. The beginning of the Global Positioning System (GPS) era in the 90s had a strong effect on the studies about τ because GPS signals allow to obtain the vTEC up to about 20000 km of altitude. Recently, τ has also found application in many data-assimilation methodologies, especially for the improvement of empirical ionospheric models based on near real-time data. All of these topics are reviewed and discussed in this paper based on the literature published in the last sixty years. Moreover, to highlight and summarize the main global climatological features of τ, in this work we selected thirty-two ionospheric stations globally distributed and co-located with ground-based Global Navigation Satellite System (GNSS) receivers, for the last two solar cycles. This allowed to collect a dataset of NmF2 and vTEC that represents the largest and most complete ever analyzed for studies concerning τ, which gave the chance to deeply investigate its spatial, diurnal, seasonal, and solar activity variations. The corresponding results are presented and discussed in the light of the existing literature.
 
Top-cited authors
David Mccomas
  • Princeton University
Adam Szabo