S. Mottola

German Aerospace Center (DLR), Köln, North Rhine-Westphalia, Germany

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Publications (307)480.88 Total impact

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    ABSTRACT: Using our photometric observations taken between April 1996 and January 2013 and other published data, we derive properties of the binary near-Earth asteroid (175706) 1996 FG3 including new measurements constraining evolution of the mutual orbit with potential consequences for the entire binary asteroid population. We also refined previously determined values of parameters of both components, making 1996 FG3 one of the most well understood binary asteroid systems. We determined the orbital vector with a substantially greater accuracy than before and we also placed constraints on a stability of the orbit. Specifically, the ecliptic longitude and latitude of the orbital pole are 266{\deg} and -83{\deg}, respectively, with the mean radius of the uncertainty area of 4{\deg}, and the orbital period is 16.1508 +\- 0.0002 h (all uncertainties correspond to 3sigma). We looked for a quadratic drift of the mean anomaly of the satellite and obtained a value of 0.04 +\- 0.20 deg/yr^2, i.e., consistent with zero. The drift is substantially lower than predicted by the pure binary YORP (BYORP) theory of McMahon and Scheeres (McMahon, J., Scheeres, D. [2010]. Icarus 209, 494-509) and it is consistent with the theory of an equilibrium between BYORP and tidal torques for synchronous binary asteroids as proposed by Jacobson and Scheeres (Jacobson, S.A., Scheeres, D. [2011]. ApJ Letters, 736, L19). Based on the assumption of equilibrium, we derived a ratio of the quality factor and tidal Love number of Q/k = 2.4 x 10^5 uncertain by a factor of five. We also derived a product of the rigidity and quality factor of mu Q = 1.3 x 10^7 Pa using the theory that assumes an elastic response of the asteroid material to the tidal forces. This very low value indicates that the primary of 1996 FG3 is a 'rubble pile', and it also calls for a re-thinking of the tidal energy dissipation in close asteroid binary systems.
    06/2014;
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    ABSTRACT: The NASA Dawn spacecraft acquired thousands of images of asteroid Vesta during its year-long orbital tour, and is now on its way to asteroid Ceres. A method for calibrating images acquired by the onboard Framing Camera was described by Schröder et al. (2013; Icarus 226, 1304). However, their method is only valid for point sources. In this paper we extend the calibration to images of extended sources like Vesta. For this, we devise a first-order correction for in-field stray light, which is known to plague images taken through the narrow band filters, and revise the flat fields that were acquired in an integrating sphere before launch. We used calibrated images of the Vesta surface to construct simple photometric models for all filters, that allow us to study how the spectrum changes with increasing phase angle (phase reddening). In combination with these models, our calibration method can be used to create near-seamless mosaics that are radiometrically accurate to a few percent. Such mosaics are provided in JVesta, the Vesta version of the JMARS geographic information system.
    Icarus 05/2014; 234:99-108. · 3.16 Impact Factor
  • Article: 2014 HF124
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    ABSTRACT: Abstract available on the publisher website.
    03/2014;
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    ABSTRACT: MASCOT on Hayabusa-2 will carry four instruments, including a wide-angle camera. We describe science goals, instrument design, and performance of the camera.
    02/2014;
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    ABSTRACT: The object was discovered in August 2013, displaying a cometary tail, but its orbital elements indicated that it was a typical member of the inner asteroid main belt. We monitored the object from 2013 August 30 until 2013 October 05 using the CFHT 3.6 m telescope (Mauna Kea, HI), the NTT (ESO, La Silla), the CA 1.23 m telescope (Calar Alto), the Perkins 1.8m (Lowell) and the 0.6 m TRAPPIST telescope (La Silla). We measured its nuclear radius to be r ≲ 0.25-0.29 km, and its colours g' - r' = 0.58 ± 0.05 and r' - i' = 0.23 ± 0.06, typical for an S-class asteroid, as expected for an object in the inner asteroid belt and in the vicinity of the Flora collisional family. We failed to detect any rotational light curve with an amplitude <0.05 mag and a double-peaked rotation period <20 h. The evolution of the tail during the observations was as expected from a dust tail. A detailed Finson-Probstein analysis of deep images acquired with the NTT in early September and with the CFHT in late September indicated that the object was active since at least late January 2013 until the time of the latest observations in 2013 September, with at least two peaks of activity around 2013 June 14 ± 10 d and 2013 July 22 ± 3 d. The changes of activity level and the activity peaks were extremely sharp and short, shorter than the temporal resolution of our observations (~1 d). The dust distribution was similar during these two events, with dust grains covering at least the 1-1000 μm range. The total mass ejected in grains <1 mm was estimated to be 3.0 × 106 kg and 2.6 × 107 kg around the two activity peaks. Rotational disruption cannot be ruled out as the cause of the dust ejection. We also propose that the components of a contact binary might gently rub and produce the observed emission. Volatile sublimation might also explain what appears as cometary activity over a period of 8 months. However, while main belt comets best explained by ice sublimation are found in the outskirts of the main belt, where water ice is believed to be able to survive buried in moderately large objects for the age of the solar system deeply, the presence of volatiles in an object smaller than 300 m in radius would be very surprising in the inner asteroid belt.Based on observations collected at the European Southern Observatory, La Silla, Chile (NTT), program 184.C-1143(H), the Canada France Hawaii Telescope, Mauna Kea, Hawaii, and the 1.2 m telescope on Calar Alto, Spain.
    02/2014;
  • Conference Paper: The colors of Vesta
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    ABSTRACT: NASA’s Dawn spacecraft entered orbit of the inner main-belt asteroid 4 Vesta on July 16, 2011, and spent 14 months in orbit to characterize the geology, elemental and mineralogical composition, topography, shape, and internal structure of Vesta before it departed to asteroid 1 Ceres in September 2012. One of the major goals of the mission is a global color mapping of Vesta.
    Vesta in the light of Dawn; 02/2014
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    ABSTRACT: We summarize the globally averaged photometric properties of Vesta and the comparisons with other rocky bodies in the solar system, and discuss the implications in both photometric properties and photometric modeling.
    01/2014;
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    ABSTRACT: Dawn's satellite working group planned and executed a satellite search upon approach to Vesta. We report efforts to determine our upper limits of detection and completion. No satellites were found with 50% completeness to apparent visual magnitude 20.54.
    01/2014;
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    ABSTRACT: P/2013 P5 PANSTARRS was discovered in Aug. 2013, displaying a cometary tail, but with orbital elements typical for a member of the inner asteroid Main Belt. We monitored the object from 2013 Aug. 30 until Oct. 05 using the CFHT, NTT, CA 1.23m, Perkins 1.8m (Lowell), and the 0.6m TRAPPIST telescopes. We measured its nuclear radius to be r < 0.25-0.29km, and its colours g-r = 0.58+/-0.05 and r-i = 0.23+/-0.06, typical for an S-class asteroid. We failed to detect any rotational light curve, with an amplitude < 0.05mag and a double-peaked rotation period < 20h. A detailed Finson-Probstein analysis of deep NTT and CFHT images indicated that the object was active since at least late January 2013 until the time of the latest observations in 2013 September, with at least two peaks of activity around 2013 June 14+/-10d and 2013 July 22+/-3d. The changes of activity level and the activity peaks were extremely sharp and short, shorter than the temporal resolution of our observations (about 1d). The dust distribution was similar during these two events, with dust grains covering at least the 1-1000{\mu}m range. The total mass ejected in grains <1mm was estimated to be 3.0 10$^6$kg and 2.6 10$^7$kg around the two activity peaks. Rotational disruption cannot be ruled out as the cause of the dust ejection. We also propose that the components of a contact binary might gently rub and produce the observed emission. Volatile sublimation might also explain what appears as cometary activity over a period of 8 months. However, while Main Belt comets best explained by ice sublimation are found in the outskirts of the Main Belt, where water ice is believed to be able to survive buried in moderately large objects for the age of the solar system deeply, the presence of volatiles in an object smaller than 300m in radius would be very surprising in the inner asteroid belt.
    01/2014;
  • Stefano Mottola, Paul Schenk, Harald Hiesinger
    Planetary and Space Science 01/2014; · 2.11 Impact Factor
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    ABSTRACT: Events such as GRB130606A at z=5.91, offer an exciting new window into pre-galactic metal enrichment in these very high redshift host galaxies. We study the environment and host galaxy of GRB 130606A, a high-z event, in the context of a high redshift population of GRBs. We have obtained multiwavelength observations from radio to gamma-ray, concentrating particularly on the X-ray evolution as well as the optical photometric and spectroscopic data analysis. With an initial Lorentz bulk factor in the range \Gamma_0 ~ 65-220, the X-ray afterglow evolution can be explained by a time-dependent photoionization of the local circumburst medium, within a compact and dense environment. The host galaxy is a sub-DLA (log N (HI) = 19.85+/-0.15), with a metallicity content in the range from ~1/7 to ~1/60 of solar. Highly ionized species (N V and Si IV) are also detected. This is the second highest redshift burst with a measured GRB-DLA metallicity and only the third GRB absorber with sub-DLA HI column density. GRB ' lighthouses' therefore offer enormous potential as backlighting sources to probe the ionization and metal enrichment state of the IGM at very high redshifts for the chemical signature of the first generation of stars.
    12/2013;
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    ABSTRACT: There have been previous hints that the transiting planet WASP-3 b is accompanied by a second planet in a nearby orbit, based on small deviations from strict periodicity of the observed transits. Here we present 17 precise radial velocity measurements and 32 transit light curves that were acquired between 2009 and 2011. These data were used to refine the parameters of the host star and transiting planet. This has resulted in reduced uncertainties for the radii and masses of the star and planet. The radial-velocity data and the transit times show no evidence for an additional planet in the system. Therefore, we have determined the upper limit on the mass of any hypothetical second planet, as a function of its orbital period.
    Astronomical Journal. 12/2013; 146(6).
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    ABSTRACT: Maria family is regarded as an old-type (~3 +/- 1 Gyr) asteroid family which has experienced substantial collisional and dynamical evolution in the Main-belt. It is located nearby the 3:1 Jupter mean motion resonance area that supplies Near-Earth asteroids (NEAs) to the inner Solar System. We carried out observations of Maria family asteroids during 134 nights from 2008 July to 2013 May, and derived synodic rotational periods for 51 objects, including newly obtained periods of 34 asteroids. We found that there is a significant excess of fast and slow rotators in observed rotation rate distribution. The two-sample Kolmogorov-Smirnov test confirms that the spin rate distribution is not consistent with a Maxwellian at a 92% confidence level. From correlations among rotational periods, amplitudes of lightcurves, and sizes, we conclude that the rotational properties of Maria family asteroids have been changed considerably by non-gravitational forces such as the YORP effect. Using a lightcurve inversion method (Kaasalainen & Torppa 2001; Kaasalainen et al. 2001), we successfully determined the pole orientations for 13 Maria members, and found an excess of prograde versus retrograde spins with a ratio (N_p/N_r) of 3. This implies that the retrograde rotators could have been ejected by the 3:1 resonance into the inner Solar System since the formation of Maria family. We estimate that approximately 37 to 75 Maria family asteroids larger than 1 km have entered the near-Earth space every 100 Myr.
    The Astronomical Journal 11/2013; 147(3). · 4.97 Impact Factor
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    ABSTRACT: Dawn spacecraft orbited Vesta for more than one year and collected a huge volume of multispectral, high-resolution data in the visible wavelengths with the Framing Camera. We present a detailed disk-integrated and disk-resolved photometric analysis using the Framing Camera images with the Minnaert model and the Hapke model, and report our results about the global photometric properties of Vesta. The photometric properties of Vesta show weak or no dependence on wavelengths, except for the albedo. At 554 nm, the global average geometric albedo of Vesta is 0.38+/-0.04, and the Bond albedo range is 0.20+/-0.02. The bolometric Bond albedo is 0.18+/-0.01. The phase function of Vesta is similar to those of S-type asteroids. Vesta's surface shows a single-peaked albedo distribution with a full-width-half-max ~17% relative to the global average. This width is much smaller than the full range of albedos (from ~0.55x to >2x global average) in localized bright and dark areas of a few tens of km in sizes, and is probably a consequence of significant regolith mixing on the global scale. Rheasilvia basin is about 10% brighter than the global average. The phase reddening of Vesta measured from Dawn Framing Camera images is comparable or slightly stronger than that of Eros as measured by the Near Earth Asteroid Rendezvous mission, but weaker than previous measurements based on ground-based observations of Vesta and laboratory measurements of HED meteorites. The photometric behaviors of Vesta are best described by the Hapke model and the Akimov disk- function, when compared with the Minnaert model, Lommel-Seeliger model, and Lommel- Seeliger-Lambertian model. The traditional approach for photometric correction is validated for Vesta for >99% of its surface where reflectance is within +/-30% of global average.
    Icarus 11/2013; 226(2):1252-1274. · 3.16 Impact Factor
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    ABSTRACT: We present a method for calibrating images acquired by the Dawn Framing Camera (FC) that is based on the results of an in-flight calibration campaign performed during the cruise from Earth to Vesta. We describe this campaign and the data analysis in full. Both the primary camera FC2 and the backup camera FC1 are radiometrically and geometrically calibrated through observations of standard stars, star fields, and Solar System objects. The calibration in each spectral filter is accurate to within a few percent for point sources. Geometric distortion, small by design, is characterized with high accuracy. Dark current, monitored on a regular basis, is very low at flight operational temperatures. Out-of-field stray light was characterized using the Sun as a stray light source. In-field stray light is confirmed in narrow-band filter images of Vesta. Its magnitude and distribution are scene-dependent, and expected to contribute significantly to images of extended objects. Description of a method for in-field stray light correction is deferred to a follow-up paper, as is a discussion of the closely related topic of flat-fielding.
    Icarus 11/2013; 226:1304-1317. · 3.16 Impact Factor
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    ABSTRACT: Comet 49P/Arend-Rigaux is well known as a low-activity Jupiter Family comet. Previous observations suggest that 49P might become purely asteroidal in appearance so by studying it over several apparitions we can start to understand this process. However on March 27, 2012 (160 days after perihelion) we discovered that comet 49P had a prominent jet pointing at an approximate position angle of 180 degrees (south) and a tail at about 270 degrees (west). The projected extent of the jet was ~9.3 x104 km and the projected tail was ~2.3x105 km long. Searching amateur archives (at http://comet.observations.free.fr) showed that the jet appeared somewhere between March 16 and March 23. We obtained follow-up observations on six dates between March 31 and July 10 using the 1.2m telescope on Calar Alto and the UH 2.2m telescope on Mauna Kea. On March 31 the jet was still present but appeared more separated from the comet, on April 15 we observed minor remnants of activity near the surface of the comet in the same region, and by June 5 the nucleus appeared stellar. To understand this outgassing event, we used 26 nights of data over 4 apparitions between 1985 and 2012 to model the heliocentric light curve. Ice sublimation models were consistent with water-ice sublimation as the volatile driving activity on 49P. Our initial models show no evidence for a secular decrease in activity. Preliminary results on two consecutive apparitions suggest a grain size of ~20 μm and a fractional active area of about 0.6% which is consistent with the low activity. Finson-Probstein (FP) dust dynamical models (Farnham, 1992) show that the data from the 1992 apparition consisted of emission of large grains emitted (up to 2 mm) with very low emission velocities near 1 m s-1 (Farnham, 1996). We will present our results from running FP models for the 2012 apparition to determine a grain size distribution and emission velocity and compare this with the 1992 apparition. We will also show how these results constrain the ice sublimation models to get better estimates of grain sizes and fractional active area.
    10/2013;
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    ABSTRACT: We report photometric observations for comet C/2012 S1 ISON obtained immediately after discovery (22 Sep. 2012; r = 6.28 AU) until moving into solar conjunction in mid-June 2013 using the UH2.2m, and Gemini North 8-m telescopes on Mauna Kea, the Lowell 1.8m in Flagstaff, the Calar Alto 1.2m telescope in Spain, and the VYSOS-5 and VYSOS-20 telescopes on Mauna Loa Hawai’i. An additional pre-discovery data point from the Pan STARRS1 survey extends the light curve back to 28 Jan. 2012 (r = 8.4 AU). The images showed similar tail morphology throughout this period, largely because of projection effects. Additional observations at sub-mm wavelengths using the JCMT on 15 nights between 9 March (r = 4.52 AU) and 16 June 2013 (r = 3.35 AU) were used to search for CO J(3-2), CO J(2-1), HCN J(4-3), and HCN J(3-2) rotation lines. No gas was detected, with preliminary upper limits for CO during 14-15 June (r = 3.3 AU) of Q < 6.4 x 10^27 molec/s based on the observations of the CO J(2-1) line. Using these production rates, the Q(H2O) published by Schleicher (2013; IAUC 9254), and the preliminary radius from the HST measurements (J.-Y. Li et al., 2013; STScI-2013-14) we have generated ice sublimation models consistent with the photometric light curve. The inbound light curve is likely controlled by sublimation of CO or CO2; at these distances water is not a strong contributor to the outgassing. Without more sensitive limits on CO, we cannot yet constrain which of these volatiles is controlling the activity. It is clear from the photometric light curve that the fractional active area of the nucleus increased linearly by about a factor of 2 from Jan. 2012 until mid Jan. 2013 (r ~ 5 AU) at which point the activity decreased by 30% by early May 2013. This suggests that a limited supply of volatile material was driving the current activity.
    10/2013;
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    ABSTRACT: The DLR Institute of Planetary Exploration has proposed a novel design of a space instrument accommodated on a small satellite bus (SSB) that is dedicated to the detection of inner earth objects (IEOs) from a low earth orbit (LEO). The instrument design is based on a focal plane consisting of electron multiplied CCDs (EMCCD) operating at high frame rates for compensation of the spacecraft's pointing jitter at very low effective readout noise. The CCD detectors operate at a nominal operating temperature of -80°C and at a frame rate of 5fps. It is well known, that CCD detectors are prone to space radiation. However, EMCCD, designed to detect very low light levels of a few electrons, have not yet been used in space. Therefore, investigations have been initiated and performed by DLR for evaluation of the performance of EMCCDs before and after radiation. The main scope of the investigations was the characterization of the charge transfer efficiency (CTE) at low light levels because of its key impact on the detection performance. The non-ionizing dose effects of space high energy particle radiation on the detector were simulated by 60MeV protons at two different fluence levels. The low light-CTE was measured with point light sources without and with background-light.
    Proc SPIE 10/2013;
  • Tilmann Denk, S. Mottola
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    ABSTRACT: Cassini ISS-NAC observations of the irregular moons of Saturn revealed various physical information on these objects. 16 synodic rotational periods: Hati (S43): 5.45 h; Mundilfari (S25): 6.74 h; Suttungr (S23): ~7.4 h; Kari (S45): 7.70 h; Siarnaq (S29): 10.14 h; Tarvos (S21): 10.66 h; Ymir (S19, sidereal period): 11.92220 h ± 0.1 s; Skathi (S27): ~12 h; Hyrrokkin (S44): 12.76 h; Ijiraq (S22): 13.03 h; Albiorix (S26): 13.32 h; Bestla (S39): 14.64 h; Bebhionn (S37): ~15.8 h; Kiviuq (S24): 21.82 h; Thrymr (S30): ~27 h; Erriapus (S28): ~28 h. The average period for the prograde-orbiting moons is ~16 h, for the retrograde moons ~11½ h (includes Phoebe's 9.2735 h from Bauer et al., AJ, 2004). Phase-angle dependent behavior of lightcurves: The phase angles of the observations range from 2° to 105°. The lightcurves which were obtained at low phase (<40°) show the 2-maxima/ 2-minima pattern expected for this kind of objects. At higher phases, more complicated lightcurves emerge, giving rough indications on shapes. Ymir pole and shape: For satellite Ymir, a convex-hull shape model and the pole-axis orientation have been derived. Ymir's north pole points toward λ = 230°±180°, β = -85°±10°, or RA = 100°±20°, Dec = -70°±10°. This is anti-parallel to the rotation axes of the major planets, indicating that Ymir not just orbits, but also rotates in a retrograde sense. The shape of Ymir resembles a triangular prism with edge lengths of ~20, ~24, and ~25 km. The ratio between the longest 25 km) and shortest axis (pole axis, ~15 km) is ~1.7. Erriapus seasons: The pole direction of object Erriapus has probably a low ecliptic latitude. This gives this moon seasons similar to the Uranian regular moons with periods where the sun stands very high in the sky over many years, and with years-long periods of permanent night. Hati density: The rotational frequency of the fastest rotator (Hati) is close to the frequency where the object would lose material from the surface if its bulk density would be less than ~1 g/cm3. This indicates that at least Hati is probably not an underdense object among Saturn's irregulars.
    10/2013;

Publication Stats

952 Citations
480.88 Total Impact Points

Institutions

  • 1991–2014
    • German Aerospace Center (DLR)
      • Institute of Planetary Research
      Köln, North Rhine-Westphalia, Germany
  • 2011
    • National Institute of Astrophysics
      • Institute of Physics of Interplanetary Space IFSI
      Roma, Latium, Italy
    • William Penn University
      University Park, Florida, United States
  • 2010
    • Freie Universität Berlin
      • Institute of Geological Sciences
      Berlín, Berlin, Germany
  • 2006–2009
    • University of Padova
      • Department of Geosciences
      Padua, Veneto, Italy
  • 1995–2007
    • The University of Arizona
      • Department of Planetary Sciences
      Tucson, Arizona, United States
  • 1994
    • University of Kent
      Cantorbery, England, United Kingdom