O. Groussin

Aix-Marseille Université, Marsiglia, Provence-Alpes-Côte d'Azur, France

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Publications (203)473.65 Total impact

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    ABSTRACT: We developed a new 3D shape reconstruction method which combines stereo, photoclinometry and the deformation of a triangular mesh describing the surface of the object. The method deforms the mesh - initially a sphere - until the set of synthetic images, created from the mesh (Jorda et al., SPIE 2010) match the observed one. Stereo control points can be used as a constraint in the deformation of the mesh, but it is not required at low resolutions. This new technique has been applied to images of the nucleus of comet 67P/Churyumov-Gerasimenko acquired by the OSIRIS instrument aboard the Rosetta spacecraft. The technique allowed to reconstruct the shape of the nucleus and to retrieve its rotational parameters from low-resolution images obtained with the narrow-angle camera of OSIRIS in mid-July 2014, when stereo-based techniques were still inapplicable. This model called "SHAP1" has been delivered to ESA and to the lander team in July. The technique has also been applied to higher-resolution images of the nucleus later on, using the stereo information as a constraint. A comparison of the reconstructed global and local models with those retrieved with other techniques, such as stereophotoclinometry (Gaskell et al., MPS 2008) and stereophotogrammetry (Preusker et al., PSS 2012) will be presented.
    AGU Fall Meeting 2014; 12/2014
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    L. Jorda, R. Gaskell, S. Hviid, C. Capanna, O. Groussin, P. Gutierrez, P. Lamy, F. Scholten, F. Preusker, H. U. Keller, J. Knollenberg, E. Kührt, S. Mottola, H. Sierks, C. Snodgrass, N. Thomas, J.-B. Vincent, S. Marchi, M. Massironi
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    ABSTRACT: The ROSETTA mission has reached the nucleus of comet 67P/Churyumov-Gerasimenko in early August, allowing a detailed mapping of its surface with the onboard OSIRIS imaging system, up to resolutions of 50 cm or even better in some areas. Shape reconstruction techniques have been used since July 2014 to build a very detailed 3D model of the comet surface and to retrieve highly accurate rotational parameters. The attached Figure shows an early 3D shape of the comet. The most striking property of the global shape is the presence of two clearly separated components. We use a combination of images and 3D models to quantitatively characterize their bulk and surface properties: relative position, volume, topography and roughness. The position of the center of mass and the direction of the principal axis of rotation are used to constrain the internal mass distribution. Digital terrain models, slope, gravity, and geo-referenced images of the most interesting features observed at the surface of the comet are presented and consequences for their formation are discussed. If they are detected, topographic changes which could have occured between August and December 2014 are also presented.
    AGU Fall Meeting 2014; 12/2014
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    ABSTRACT: Aims. Approach observations with the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) experiment onboard Rosetta are used to determine the rotation period, the direction of the spin axis, and the state of rotation of comet 67P's nucleus. Methods. Photometric time series of 67P have been acquired by OSIRIS since the post wake-up commissioning of the payload in March 2014. Fourier analysis and convex shape inversion methods have been applied to the Rosetta data as well to the available ground-based observations. Results. Evidence is found that the rotation rate of 67P has significantly changed near the time of its 2009 perihelion passage, probably due to sublimation-induced torque. We find that the sidereal rotation periods P 1 = 12.76129 ± 0.00005 h and P 2 = 12.4043 ± 0.0007 h for the apparitions before and after the 2009 perihelion, respectively, provide the best fit to the observations. No signs of multiple periodicity are found in the light curves down to the noise level, which implies that the comet is presently in a simple rotation state around its axis of largest moment of inertia. We derive a prograde rotation model with spin vector J2000 ecliptic coordinates λ = 65 • ± 15 • , β = +59 • ± 15 • , corresponding to equatorial coordinates RA = 22 • , Dec = +76 • . However, we find that the mirror solution, also prograde, at λ = 275 • ± 15 • , β = +50 • ± 15 • (or RA = 274 • , Dec = +27 •), is also possible at the same confidence level, due to the intrinsic ambiguity of the photometric problem for observations performed close to the ecliptic plane.
    Astronomy and Astrophysics 09/2014; 569(L2). · 4.48 Impact Factor
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    ABSTRACT: On November 4th, 2010, the Deep Impact eXtended Investigation (DIXI) successfully encountered comet 103P/Hartley 2, when it was at a heliocentric distance of 1.06 AU. Spatially resolved near-IR spectra of comet Hartley 2 were acquired in the 1.05–4.83 μm wavelength range using the HRI-IR spectrometer. We present spectral maps of the inner ∼∼10 km of the coma collected 7 min and 23 min after closest approach. The extracted reflectance spectra include well-defined absorption bands near 1.5, 2.0, and 3.0 μm consistent in position, bandwidth, and shape with the presence of water ice grains. Using Hapke’s radiative transfer model, we characterize the type of mixing (areal vs. intimate), relative abundance, grain size, and spatial distribution of water ice and refractories. Our modeling suggests that the dust, which dominates the innermost coma of Hartley 2 and is at a temperature of 300 K, is thermally and physically decoupled from the fine-grained water ice particles, which are on the order of 1 μm in size. The strong correlation between the water ice, dust, and CO2 spatial distribution supports the concept that CO2 gas drags the water ice and dust grains from the nucleus. Once in the coma, the water ice begins subliming while the dust is in a constant outflow. The derived water ice scale-length is compatible with the lifetimes expected for 1-μm pure water ice grains at 1 AU, if velocities are near 0.5 m/s. Such velocities, about three order of magnitudes lower than the expansion velocities expected for isolated 1-μm water ice particles ( and ), suggest that the observed water ice grains are likely aggregates.
    Icarus 08/2014; 238:191–204. · 2.84 Impact Factor
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    ABSTRACT: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
    Icarus 01/2014; doi. · 2.84 Impact Factor
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    ABSTRACT: Comet 103P/Hartley 2 made a close approach to the Earth in October 2010. It was the target of an extensive observing campaign and was visited by the Deep Impact spacecraft (mission EPOXI). We present observations of HCN and CH3OH emission lines conducted with the IRAM Plateau de Bure interferometer on 22-23, 28 October and 4, 5 November 2010 at 1.1, 1.9 and 3.4 mm wavelengths. The thermal emission from the dust coma and nucleus is detected simultaneously. Interferometric images with unprecedented spatial resolution are obtained. A sine-wave variation of the thermal continuum is observed in the 23 October data, that we associate with the nucleus thermal light curve. The nucleus contributes up to 30-55 % of the observed continuum. The large dust-to-gas ratio (in the range 2-6) can be explained by the unusual activity of the comet for its size, which allows decimeter size particles and large boulders to be entrained by the gas. The rotational temperature of CH3OH is measured. We attribute the increase from 35 to 46 K with increasing beam size (from 150 to 1500 km) to radiative processes. The HCN production rate displays strong rotation-induced variations. The HCN production curve, as well as those of CO2 and H2O measured by EPOXI, are interpreted with a geometric model which takes into account the rotation and the shape of the comet. The HCN and H2O production curves are in phase, showing common sources. The 1.7h delay, in average, of HCN and H2O with respect to the CO2 production curve suggests that HCN and H2O are mainly produced by subliming icy grains. The scale length of production of HCN is determined to be on the order of 500-1000 km, implying a mean velocity of 100-200 m/s for the icy grains producing HCN. The modulation of the CO2 prouction and of the velocity offset of the HCN lines are interpreted in terms of localized sources of gas on the nucleus surface.
    Icarus 10/2013; 228. · 2.84 Impact Factor
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    ABSTRACT: Deep Impact acquired a unique rotational data set during its close flyby of comet 103/P Hartley 2 (DIXI mission, November 4, 2010). The HRI-IR spectrometer (1.05-4.85 microns) monitored the coma throughout the encounter acquiring infrared scans every 2 hr over the 18 hr period prior to closest approach and every 30 min for 2 days after closest approach. Water vapor (2.7 microns), carbon dioxide (4.3 microns), and bulk organics 3.4 microns) were the dominant emission bands detected in these spectra and their distribution was found to be highly asymmetric and variable. In particular, the distribution maps from the 8 hrs following closest approach half of the dominant 18.4 hr rotation period) are unique with spatial resolutions ranging from 0.2-3.5 km/pixel. These data allow us to explore correlations among the volatiles and the role of extended coma sources. These data will also help to quantify the heterogeneity of the outgassing and better locate specific source regions on the nucleus of Hartley 2.
    10/2013;
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    ABSTRACT: THERMAP is a mid-infrared (8-16 μm) spectroimager, selected by the European Space Agency (ESA) in February 2013 for the scientific payload of the Marco Polo R M-class mission. We present in this paper the instrument and its scientific objectives.
    09/2013;
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    ABSTRACT: Aims. Trans-Neptunian objects (TNOs) are bodies populating the Kuiper belt and they are believed to retain the most pristine and least altered material of the solar system. The Herschel open time key programme entitled “TNOs are Cool: A survey of the trans-Neptunian region” has been awarded 373 h to investigate the albedo, size distribution and thermal properties of TNOs and Centaurs. Here we focus on the brightest targets observed by both the PACS and SPIRE multiband photometers: the dwarf planet Haumea, six TNOs (Huya, Orcus, Quaoar, Salacia, 2002 UX25, and 2002 TC302), and two Centaurs (Chiron and Chariklo). Methods. Flux densities are derived from PACS and SPIRE instruments using optimised data reduction methods. The spectral energy distribution obtained with the Herschel PACS and SPIRE instruments over 6 bands (centred at 70, 100, 160, 250, 350, and 500 μm), with Spitzer-MIPS at 23.7 and 71.4 μm, and with WISE at 11.6 and 22.1 μm in the case of 10199 Chariklo, has been modelled with the NEATM thermal model in order to derive the albedo, diameter, and beaming factor. For the Centaurs Chiron and Chariklo and for the 1000 km sized Orcus and Quaoar, a thermophysical model was also run to better constrain their thermal properties. Results. We derive the size, albedo, and thermal properties, including thermal inertia and surface emissivity, for the 9 TNOs and Centaurs. Several targets show a significant decrease in their spectral emissivity longwards of ∼300 μm and especially at 500 μm. Using our size estimations and the mass values available in the literature, we also derive the bulk densities for the binaries Quaoar/Weywot (2.18 (+0.43;−0.36)g/cm3), Orcus/Vanth (1.53 (+0.15; −0.13) g/cm3), and Salacia/Actea (1.29 (+0.29; −0.23) g/cm3). Quaoar’s density is similar to that of the other dwarf planets Pluto and Haumea, and its value implies high contents of refractory materials mixed with ices.
    Astronomy and Astrophysics 09/2013; · 4.48 Impact Factor
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    ABSTRACT: Little is known about the physical properties of the nuclei of Oort cloud comets. Measuring the thermal emission of a nucleus is one of the few means for deriving its size and constraining some of its thermal properties. We attempted to measure the nucleus size of the Oort cloud comet C/2009 P1 (Garradd). We used the Plateau de Bure Interferometer to measure the millimetric thermal emission of this comet at 157 GHz (1.9 mm) and 266 GHz (1.1 mm). Whereas the observations at 266 GHz were not usable due to bad atmospheric conditions, we derived a 3-sigma upper limit on the comet continuum emission of 0.41 mJy at 157 GHz. Using a thermal model for a spherical nucleus with standard thermal parameters, we found an upper limit of 5.6 km for the radius. The dust contribution to our signal is estimated to be negligible. Given the water production rates measured for this comet and our upper limit, we estimated that Garradd was very active, with an active fraction of its nucleus larger than 50%.
    Astronomy and Astrophysics 07/2013; · 4.48 Impact Factor
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    ABSTRACT: We present results from SEPPCoN, an on-going Survey of the Ensemble Physical Properties of Cometary Nuclei. In this report we discuss mid-infrared measurements of the thermal emission from 89 nuclei of Jupiter-family comets (JFCs). All data were obtained in 2006 and 2007 with the Spitzer Space Telescope. For all 89 comets, we present new effective radii, and for 57 comets we present beaming parameters. Thus our survey provides the largest compilation of radiometrically-derived physical properties of nuclei to date. We conclude the following. (a) The average beaming parameter of the JFC population is 1.03+/-0.11, consistent with unity, and indicating low thermal inertia. (b) The known JFC population is not complete even at 3 km radius, and even for comets with perihelia near ~2 AU. (c) We find that the JFC nuclear cumulative size distribution (CSD) has a power-law slope of around -1.9. (d) This power-law is close to that derived from visible-wavelength observations, suggesting that there is no strong dependence of geometric albedo with radius. (e) The observed CSD shows a hint of structure with an excess of comets with radii 3 to 6 km. (f) Our CSD is consistent with an intrinsic distribution that lacks many sub-kilometer objects.
    Icarus 07/2013; 226(1). · 2.84 Impact Factor
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    ABSTRACT: NASA’s EPOXI mission used the Deep Impact (DI) Flyby spacecraft to deliver a payload of three scientific instruments, two visible cameras and an IR spectrometer, to a close flyby of Comet 103P/Hartley 2 in November 2010. Interpretation of the scientific measurements made using these instruments depends on accurate calibration of the instruments’ performance. Updates to the instrument calibrations achieved during the Deep Impact primary mission and results of continued monitoring of their performance during EPOXI are reported here. The instruments’ performance has remained remarkably stable over the nearly 7 years of flight. Significant improvements in the understanding and calibration of the IR spectrometer response non-linearity, time-varying background level, flat field, wavelength map, and absolute spectral response have been achieved. Techniques for reducing some semi-coherent horizontal noise stripes in the visible cameras’ readouts were developed, and some adjustments have been made to their absolute radiometric conversion constants. The data processing pipeline has been updated to incorporate the improvements in the instrument calibrations.
    Icarus 07/2013; 225(1):643–680. · 2.84 Impact Factor
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    ABSTRACT: Re-calibrated near-infrared spectroscopy of the resolved nucleus of Comet 9P/Tempel 1 acquired by the Deep Impact spacecraft has been analyzed by utilizing the post-Stardust-NExT nucleus shape model and spin pole solution, as well as a novel thermophysical model that explicitly accounts for small-scale surface roughness and thermal inertia. We find that the thermal inertia varies measurably across the surface, and that thermal emission from certain regions only can be reproduced satisfactory if surface roughness is accounted for. Particularly, a scarped/pitted terrain that experienced morning sunrise during the flyby is measurably rough (Hapke mean slope angle ∼45°) and has a thermal inertia of at most 50 J m−2 K−1 s−1/2, but probably much lower. However, thick layered terrain and thin layered terrain experiencing local noon during the flyby have a substantially larger thermal inertia, reaching 150 J m−2 K−1 s−1/2 if the surface is as rough as the scarped/pitted terrain, but 200 J m−2 K−1 s−1/2 if the terrain is considered locally flat. Furthermore, the reddening of the nucleus near-infrared 1.5–2.2 μm spectrum varies between morphological units, being reddest for thick layered terrain (median value 3.4% kÅ−1) and most neutral for the smooth terrain known to contain surface water ice (median value 3.1% kÅ−1). Thus, Comet 9P/Tempel 1 is heterogeneous in terms of both thermophysical and optical properties, due to formation conditions and/or post-formation processing.
    Icarus 05/2013; 224(1):154–171. · 2.84 Impact Factor
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    ABSTRACT: We present an analysis of comet activity based on the Spitzer Space Telescope component of the Survey of the Ensemble Physical Properties of Cometary Nuclei. We show that the survey is well suited to measuring the activity of Jupiter-family comets at 3-7 AU from the Sun. Dust was detected in 33 of 89 targets (37 +/- 6%), and we conclude that 21 comets (24 +/- 5%) have morphologies that suggest ongoing or recent cometary activity. Our dust detections are sensitivity limited, therefore our measured activity rate is necessarily a lower limit. All comets with small perihelion distances (q < 1.8 AU) are inactive in our survey, and the active comets in our sample are strongly biased to post-perihelion epochs. We introduce the quantity epsilon-f-rho, intended to be a thermal emission counterpart to the often reported A-f-rho, and find that the comets with large perihelion distances likely have greater dust production rates than other comets in our survey at 3-7 AU from the Sun, indicating a bias in the discovered Jupiter-family comet population. By examining the orbital history of our survey sample, we suggest that comets perturbed to smaller perihelion distances in the past 150 yr are more likely to be active, but more study on this effect is needed.
    Icarus 04/2013; 225(1). · 2.84 Impact Factor
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    ABSTRACT: a b s t r a c t The nucleus of comet Tempel 1 has been investigated at close range during two spacecraft missions sep-arated by one comet orbit of the Sun, 5½ years. The combined imaging covers $70% of the surface of this object which has a mean radius of 2.83 ± 0.1 km. The surface can be divided into two terrain types: rough, pitted terrain and smoother regions of varying local topography. The rough surface has round depressions from resolution limits ($10 m/pixel) up to $1 km across, spanning forms from crisp steep-walled pits, to subtle albedo rings, to topographic rings, with all ranges of morphologic gradation. Three gravitationally low regions of the comet have smoother terrain, parts of which appear to be deposits from minimally modified flows, with other parts likely to be heavily eroded portions of multiple layer piles. Changes observed between the two missions are primarily due to backwasting of scarps bounding one of these probable flow deposits. This style of erosion is also suggested by remnant mesa forms in other areas of smoother terrain. The two distinct terrains suggest either an evolutionary change in processes, topo-graphically-controlled processes, or a continuing interaction of erosion and deposition.
    Icarus 02/2013; 222:453-466. · 2.84 Impact Factor
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    ABSTRACT: a b s t r a c t On February 14, 2011 Stardust-NExT (SN) flew by Comet Tempel 1, the target of the Deep Impact (DI) mission in 2005, obtaining dust measurements and high-resolution images of areas surrounding the 2005 impact site, and extending image coverage to almost two thirds of the nucleus surface. The nucleus has an average radius of 2.83 ± 0.1 km and a uniform geometric albedo of about 6% at visible wavelengths. Local elevation differences on the nucleus reach up to 830 m. At the time of encounter the spin rate was 213° per day (period = 40.6 h) and the comet was producing some 130 kg of dust per second. Some 30% of the nucleus is covered by smooth flow-like deposits and related materials, restricted to gravitational lows. This distribution is consistent with the view that the smooth areas represent material erupted from the subsurface and date from a time after the nucleus achieved its current shape. It is possible that some of these eruptions occurred after 1609 when the comet's perihelion distance decreased from 3.5 AU to the current 1.5 AU. Much of the surface displays evidence of layering: some related to the smooth flows and some possibly dating back to the accretion of the nucleus. Pitted terrain covers approximately half the nucleus surface. The pits range up to 850 m in diameter. Due to their large number, they are unlikely to be impact scars: rather they probably result from volatile outbursts and sublimational erosion. The DI impact site shows a subdued depression some 50 m in diameter implying surface properties similar to those of dry, loose snow. It is possible that the 50-m depression is all that remains of an initially larger crater. In the region of overlapping DI and SN coverage most of the surface remained unchanged between 2005 and 2011 in albedo, photometric properties and morphology. Significant changes took place only along the edges of a prominent smooth flow estimated to be 10–15 m thick, the margins of which receded in places by up to 50 m. Coma and jet activity were lower in 2011 than in 2005. Most of the jets observed during the SN flyby can be traced back to an apparently eroding terraced scarp. The dust instruments detected bursts of impacts consistent with a process by which larger aggregates of material emitted from the nucleus subsequently fragment into smaller particles within the coma.
    Icarus 02/2013; 222:424-435. · 2.84 Impact Factor
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    ABSTRACT: a b s t r a c t The Deep Impact spacecraft flew by Comet 103P/Hartley 2 on November 4th, 2010 (EPOXI mission) and Comet 9P/Tempel 1 on July 4th, 2005 (Deep Impact mission). During the two flybys, spatially resolved infrared (1.05–4.8 lm) spectra of the surface of the nucleus were acquired by the HRI-IR instrument. The analysis of these two data sets, obtained by the same instrument, offers a unique opportunity to understand, compare and contrast the surface thermal properties of these two comets. For this paper, we use spectral cubes with a spatial resolution of 30 m/pixel to 40 m/pixel for Hartley 2 and 160 m/pixel for Tempel 1. We focus our analysis on the color, temperature, thermal inertia and roughness of the nucleus. The two comets have the same color, moderately red, with an average slope of 3.0 ± 0.9% per kÅ to 3.5 ± 1.1% per kÅ. There are very small variations of the color across the surface, except for regions with water ice that are neutral to blue, and two dark spots with redder (4.5 ± 1.4% per kÅ) materials on Hart-ley 2. The nucleus thermal emission at all resolved spatial scales differs from that of a gray body with an infrared emissivity of 0.9–1.0, the discrepancy being more important for larger incidence angles. More-over, the color temperature of Comets Hartley 2 and Tempel 1 is relatively homogeneous across the sur-face and does not vary strongly with incidence angle. These two effects mainly result from surface roughness and associated projected shadows. From the temperature rise on the morning terminator, we derive a thermal inertia lower than 250 W/K/m 2 /s 1/2 for Hartley 2 and lower than 45 W/K/m 2 /s 1/2 for Tempel 1 (3r upper limits). For Hartley 2 and Tempel 1, the temperature of the regions with exposed water ice is more than 100 K above the sublimation temperature of water ice ($200 K). This observation indicates that the thermal emission is dominated by dust, and that water ice is not intimately mixed with dust at the scale of observation, with water ice patches at the meter or sub-meter scale.
    Icarus 02/2013; 222:580-594. · 2.84 Impact Factor
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    ABSTRACT: a b s t r a c t Data from the Extrasolar Planet Observation and Deep Impact Extended Investigation (EPOXI) mission show Comet 103P/Hartley 2 is a bi-lobed, elongated, nearly axially symmetric comet 2.33 km in length. Surface features are primarily small mounds <40 m across, irregularly-shaped smooth areas on the two lobes, and a smooth but variegated region forming a ''waist'' between the two lobes. Assuming parts of the comet body approach the shape of an equipotential surface, the mean density of Hartley 2 is modeled to be 200–400 kg m À3 . Such a mean density suggests mass loss per orbit of >1%. The shape may be the evolutionary product of insolation, sublimation, and temporary deposition of materials controlled by the object's complex rotation.
    Icarus 02/2013; 222:550-558. · 2.84 Impact Factor
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    ABSTRACT: Aims. The goal of this work is to characterize the ensemble thermal properties of the Centaurs / trans-Neptunian population. Methods. Thermal flux measurements obtained with Herschel/PACS and Spitzer/MIPS provide size, albedo, and beaming factors for 85 objects (13 of which are presented here for the first time) by means of standard radiometric techniques. The measured beaming factors are influenced by the combination of surface roughness and thermal inertia effects. They are interpreted within a thermophysical model to constrain, in a statistical sense, the thermal inertia in the population and to study its dependence on several parameters. We use in particular a Monte-Carlo modeling approach to the data whereby synthetic datasets of beaming factors are created using random distributions of spin orientation and surface roughness. Results. Beaming factors η range from values <1 to ~2.5, but high η values (>2) are lacking at low heliocentric distances (rh < 30 AU). Beaming factors lower than 1 occur frequently (39% of the objects), indicating that surface roughness effects are important. We determine a mean thermal inertia for Centaurs/ TNO of Γ = (2.5 ± 0.5) J m-2 s−1/2 K-1, with evidence of a trend toward decreasing Γ with increasing heliocentric (by a factor ~2.5 from 8–25 AU to 41–53 AU). These thermal inertias are 2–3 orders of magnitude lower than expected for compact ices, and generally lower than on Saturn’s satellites or in the Pluto/Charon system. Most high-albedo objects are found to have unusually low thermal inertias. Our results suggest highly porous surfaces, in which the heat transfer is affected by radiative conductivity within pores and increases with depth in the subsurface.
    Astronomy and Astrophysics 01/2013; 557(2013-A60):1-19. · 4.48 Impact Factor
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    ABSTRACT: The Rosetta spacecraft flew by Asteroid (2867) Steins on 5 September 2008, allowing the onboard OSIRIS cameras to collect the first images of an E-type asteroid. We implemented several three-dimensional reconstruction techniques to retrieve its shape. Limb profiles, combined with stereo control points, were used to reconstruct an approximate shape model. This model was refined using a stereophotoclinometry technique to accurately retrieve the topography of the hemisphere observed by OSIRIS. The unseen part of the surface was constrained by the technique of light curves inversion.The global shape resembles a top with dimensions along the principal axes of inertia of 6.83 × 5.70 × 4.42 km. It is conspicuously more regular than other small asteroids like (233) Eros and (25143) Itokawa. Its mean radius is Rm = 2.70 km and its equivalent radius (radius of a sphere of equivalent volume) is Rv = 2.63 km. The north pole is oriented at RA = 99 ± 5° and Dec = −59 ± 5°, which implies a very large obliquity of 172° and a retrograde rotation.Maps of the gravitational field and slopes were calculated for the well-imaged part of the asteroid. Together with the shape, they helped characterizing the most prominent topographic features identified at the surface of (2867) Steins: an equatorial ridge restricted to the extremities of the long axis, a large crater having dimensions of 2100 × 1800 m in the southern hemisphere, and an elongated hill in the northern hemisphere. We conjecture that the equatorial ridge was formed by centrifugal acceleration as the asteroid was spun up by the Yarkovsky–O’Keefe–Radzievskii–Paddack effect.
    Icarus 11/2012; 221(2):1089–1100. · 2.84 Impact Factor

Publication Stats

2k Citations
473.65 Total Impact Points

Institutions

  • 2012–2014
    • Aix-Marseille Université
      • Laboratory of Astrophysics of Marseille (UMR 7326 LAM)
      Marsiglia, Provence-Alpes-Côte d'Azur, France
  • 2010–2011
    • Observatoire Astrophysique de Marseille Provence
      • Laboratory of Astrophysics of Marseille
      Marsiglia, Provence-Alpes-Côte d'Azur, France
  • 2006–2008
    • University of Maryland, College Park
      • Department of Astronomy
      Maryland, United States
    • Johns Hopkins University
      • Applied Physics Laboratory
      Baltimore, Maryland, United States
  • 2007
    • Cornell University
      • Center for Radiophysics and Space Research (CRSR)
      New York City, NY, United States
  • 2005–2007
    • Loyola University Maryland
      Baltimore, Maryland, United States
    • University of Hawaiʻi at Mānoa
      • Institute of Astronomy
      Honolulu, HI, United States