Compositional interpretation of PFS/MEx and TES/MGS thermal infrared spectra of Phobos

Abstract The origin of the Martian satellites presents a puzzle of long standing. Addressing the composition of Phobos will help constrain theories of its formation. Visible and near-infrared spectra of Phobos lack deep absorption features, making the compositional interpretation a tricky task. PFS/MEx and TES/MGS observations in the thermal infrared show several spectral features that can be used to investigate the composition of the surface. Our results show that the majority of the spectra are consistent with the presence of phyllosilicates, particularly in the area northeast of Stickney. This area corresponds to the “blue” region as defined by Murchie et al. (1999) . Analysis of PFS and TES observations in the “red” region defined by Murchie et al. (1999) are consistent with tectosilicates, especially feldspars/feldspathoids. We discuss several physical and chemical mechanisms that can act to eliminate or reduce the strength of bands in the VIS/NIR spectra, with possibly little or no effect in the mid-IR. Comparison of the TES and PFS data to the meteorites shows that no class of chondritic meteorites provide significant agreement with the spectral features observed. The lack of consistency of the PFS and TES spectra to analogs of ultraprimitive materials (organic residues) suggests that an origin via capture of a transneptunian object is not supported by these observations, although it cannot be completely ruled out. Derived surface temperatures from PFS and TES data are in very good agreement with brightness temperatures derived from Viking orbiter measurements, Earth-based observations, and values predicted by numerical models. Our results show that the surface temperature of Phobos varies with solar incidence angle and heliocentric distance, reconciling the different results. We collect and summarize the compositional clues for the origin of Phobos discussed in this paper, including our results. Currently, the most likely scenario is the in-situ formation of Phobos, although a capture of achrondrite-like meteorites is not ruled out.

[1]  S. Sasaki,et al.  Space weathering on Mercury , 2002 .

[2]  W. Hartmann,et al.  Solid CN bearing material on outer solar system bodies , 1991 .

[3]  V. M. Murav’ev,et al.  Results of TV imaging of Phobos (Experiment VSK-Fregat). , 1991, Planetary and space science.

[4]  Scott L. Murchie,et al.  Color Heterogeneity of the Surface of Phobos' Relationships to Geologic Features and Comparison to Meteorite Analogs , 1991 .

[5]  Johan Warell,et al.  A set of laboratory analogue materials for the MERTIS instrument on the ESA BepiColombo mission to Mercury , 2006 .

[6]  R. Jaumann,et al.  HRSC: the High Resolution Stereo Camera of Mars Express , 2004 .

[7]  Dorian G. W. Smith,et al.  Reflectance spectra of 'featureless' materials and the surface mineralogies of M- and E-class asteroids , 1990 .

[8]  K. Tsiganis,et al.  Origin of the orbital architecture of the giant planets of the Solar System , 2005, Nature.

[9]  D. Britt,et al.  Phobos: Spectrophotometry between 0.3 and 0.6 μm and IR-radiometry , 1991 .

[10]  R. W. Le Maitre,et al.  A Classification of igneous rocks and glossary of terms : recommendations of the International Union of Geological Sciences Subcommission on the Systematics of Igneous Rocks , 1989 .

[11]  B. Hapke,et al.  Asteroid Space Weathering and Regolith Evolution , 2002 .

[12]  Michael J. Gaffey,et al.  Metal silicate mixtures - Spectral properties and applications to asteroid taxonomy , 1990 .

[13]  David Crisp,et al.  The planetary fourier spectrometer (PFS) onboard the European Venus Express mission , 2005 .

[14]  Scott L. Murchie,et al.  Spectral Properties and Heterogeneity of PHOBOS from Measurements by PHOBOS 2 , 1996 .

[15]  R. Singer.  Near-infrared spectral reflectance of mineral mixtures - Systematic combinations of pyroxenes, olivine, and iron oxides , 1981 .

[16]  J. Warell,et al.  Properties of the hermean regolith: iii. disk-resolved vis-NIR reflectance spectra and implications for the abundance of iron* , 2003 .

[17]  Sho Sasaki,et al.  Developing space weathering on the asteroid 25143 Itokawa , 2006, Nature.

[18]  K. Tsiganis,et al.  Origin of the cataclysmic Late Heavy Bombardment period of the terrestrial planets , 2005, Nature.

[19]  R. A. Jacobson,et al.  THE ORBITS AND MASSES OF THE MARTIAN SATELLITES AND THE LIBRATION OF PHOBOS , 2010 .

[20]  Ted L. Roush,et al.  Comparison of Laboratory Emission Spectra with Mercury Telescopic Data , 1998 .

[21]  Agustin Chicarro,et al.  Mars express : the scientific payload , 2004 .

[22]  A. Streckeisen,et al.  The IUGS systematics of igneous rocks , 1991, Journal of the Geological Society.

[23]  M. Paetzold,et al.  Revisiting Phobos' origin issue from Mars Express Radio-Science observations. , 2010 .

[24]  M. Birlan,et al.  Solar wind as the origin of rapid reddening of asteroid surfaces , 2009, Nature.

[25]  Dorian G. W. Smith,et al.  Reflectance spectra of glass-bearing mafic silicate mixtures and spectral deconvolution procedures , 1990 .

[26]  A. McEwen,et al.  Mars Reconnaissance Orbiter's High Resolution Imaging Science Experiment (HiRISE) , 2007 .

[27]  L. Maitre.  The Chemical Variability of some Common Igneous Rocks , 1976 .

[28]  R. Trautner,et al.  The Mars Express mission: an overview , 2004 .

[29]  D. L. Anderson,et al.  Thermal emission spectrometer experiment: Mars Observer mission , 1992 .

[30]  Dah-Ning Yuan,et al.  A global solution for the Mars static and seasonal gravity, Mars orientation, Phobos and Deimos masses, and Mars ephemeris , 2006 .

[31]  J. Mustard,et al.  Effects of Hyperfine Particles on Reflectance Spectra from 0.3 to 25 μm , 1997 .

[32]  Accurate Mars Express orbits to improve the determination of the mass and ephemeris of the Martian moons , 2008 .

[33]  M. J. Bas.  Nephelinitic and Basanitic Rocks , 1989 .

[34]  M. Ramsey,et al.  Mineral abundance determination: Quantitative deconvolution of thermal emission spectra , 1998 .

[35]  Dorian G. W. Smith,et al.  Reflectance spectra of mafic silicate-opaque assemblages with applications to meteorite spectra , 1990 .

[36]  R. Clark,et al.  Results from the Mars Global Surveyor Thermal Emission Spectrometer. , 1998, Science.

[37]  T. McCord,et al.  Alteration of Lunar Optical Properties: Age and Composition Effects , 1971, Science.

[38]  V. Dehant,et al.  Precise mass determination and the nature of Phobos , 2010 .

[39]  Giuseppe Piccioni,et al.  Calibration of the Planetary Fourier Spectrometer short wavelength channel , 2005 .

[40]  P. Brown,et al.  The fall and recovery of the Tagish Lake meteorite , 2006 .

[41]  D. A. Howard,et al.  A thermal emission spectral library of rock-forming minerals , 2000 .

[42]  Bruce M. Jakosky,et al.  Infrared observations of Phobos and Deimos from Viking , 1982 .

[43]  Joseph A. Burns,et al.  Contradictory clues as to the origin of the Martian moons , 1992 .

[44]  Lionel Wilson,et al.  Photometric observations of Mercury from Mariner 10 , 1975 .

[45]  Clark R. Chapman,et al.  SPACE WEATHERING OF ASTEROID SURFACES , 2004 .

[46]  D. Trilling,et al.  Near-Infrared Spectrophotometry of Phobos and Deimos , 2002 .

[47]  R. Craddock,et al.  Are Phobos and Deimos the result of a giant impact , 2011 .

[48]  Carle M. Pieters,et al.  RELAB (Reflectance Experiment Laboratory): A NASA Multiuser Spectroscopy Facility , 2004 .

[49]  P. Christensen,et al.  Quantitative thermal emission spectroscopy of minerals: A laboratory technique for measurement and calibration , 1997 .

[50]  John W. Salisbury,et al.  Compositional Implications of Christiansen Frequency Maximums for Infrared Remote Sensing Applications , 1973 .

[51]  Raymond E. Arvidson,et al.  Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on Mars Reconnaissance Orbiter (MRO) , 2007 .

[52]  T. Roush,et al.  Mars Global Surveyor Thermal Emission Spectrometer Observations of Phobos , 2000 .

[53]  James E. Conel,et al.  Infrared emissivities of silicates: Experimental results and a cloudy atmosphere model of Spectral emission from condensed particulate mediums , 1969 .

[54]  M. Gaffey,et al.  Metal-Orthopyroxene and Metal-Olivine Mixtures: Spectral Reflectance Properties and Implications for Asteroid Spectroscopy , 2009 .

[55]  Jürgen Oberst,et al.  Phobos control point network, rotation, and shape , 2010 .

[56]  C. Pieters.  LUNAR MATERIALS FROM THE VISIBLE TO MID-INFRARED : THE EFFECTS OF SPACE WEATHERING , 1998 .

[57]  John W. Salisbury,et al.  Midinfrared (2.5–13.5 μm) reflectance spectra of powdered stony meteorites , 1991 .

[58]  A. Streckeisen.  To each plutonic rock its proper name , 1976 .

[59]  D. B. Nash,et al.  Spectral reflectance and albedo of Apollo 11 lunar samples - Effects of irradiation and vitrification and comparison with telescopic observations , 1970 .

[60]  M. Darby Dyar,et al.  Spectroscopy of synthetic Mg‐Fe pyroxenes I: Spin‐allowed and spin‐forbidden crystal field bands in the visible and near‐infrared , 2007 .

[61]  H. Melosh,et al.  Gravitational Aggregates: Evidence and Evolution , 2002 .

[62]  S. Erard,et al.  ISM observation of Phobos reinvestigated: Identification of a mixture of olivine and low‐calcium pyroxene , 2005 .

[63]  Richard C. Puetter,et al.  Infrared Spectra of Deimos (1-13 μm) and Phobos (3-13 μm) , 2007 .

[64]  E. Fischer,et al.  THERMAL INFRARED SPECTRA OF LUNAR SOILS , 1997 .

[65]  David A. Naylor,et al.  Apodizing functions for Fourier transform spectroscopy , 2007 .

[66]  S. Murchie,et al.  Spectroscopic Observations of Mercury's Surface Reflectance During MESSENGER's First Mercury Flyby , 2008, Science.

[67]  Interpretation of the KRFM-infrared measurements of phobos , 1992 .

[68]  Bruce Hapke,et al.  Space weathering from Mercury to the asteroid belt , 2001 .

[69]  S. Murchie,et al.  MRO/CRISM Observations of Phobos and Deimos , 2008 .

[70]  Roger G. Burns,et al.  Mineralogical applications of crystal field theory , 1970 .

[71]  R. Kuzmin,et al.  The Temperature Regime of the Surface Layer of the Phobos Regolith in the Region of the Potential Fobos–Grunt Space Station Landing Site , 2003 .

[72]  F. Fanale,et al.  Loss of water from Phobos , 1989 .

[73]  Faith Vilas,et al.  Mercury: Absence of crystalline Fe2+ in the regolith , 1985 .

[74]  A. Albee,et al.  Mars global surveyor mission: overview and status. , 1998, Science.

[75]  John W. Salisbury,et al.  Thermal infrared (2.5–13.5 μm) spectroscopic remote sensing of igneous rock types on particulate planetary surfaces , 1989 .

[76]  C. Pieters,et al.  Remote geochemical analysis : elemental and mineralogical composition , 1993 .

[77]  J. P. Bibring,et al.  Spatial variations in thermal and albedo properties of the surface of Phobos , 1989, Nature.

[78]  Nicolas Thomas,et al.  Spectral heterogeneity on Phobos and Deimos: HiRISE observations and comparisons to Mars Pathfinder results , 2010 .

[79]  V. N. Heifets,et al.  Television observations of Phobos , 1989, Nature.

[80]  Scott L. Murchie,et al.  Mars Pathfinder spectral measurements of Phobos and Deimos: Comparison with previous data , 1999 .

[81]  Gabriele Arnold,et al.  Grain-size influence on the mid-infrared spectra of the minerals , 1988 .

[82]  T. McCord,et al.  Optical properties of mineral separates, glass, and anorthositic fragments from Apollo mare samples , 1971 .

[83]  Thomas C. Duxbury,et al.  The figure of Phobos , 1989 .