A NEAR-INFRARED SEARCH FOR SILICATES IN JOVIAN TROJAN ASTEROIDS

We obtained near-infrared (NIR; 0.8–2.5 μm) spectra of seven Jovian Trojan asteroids that have been formerly reported to show silicate-like absorption features near 1 μm. Our sample includes the Trojan (1172) Aneas, which is one of the three Trojans known to possess a comet-like 10 μm emission feature, indicative of fine-grained silicates. Our observations show that all seven Trojans appear featureless in high signal-to-noise ratio spectra. The simultaneous absence of the 1 μm band and the presence of the 10 μm emission can be understood if the silicates on (1172) Aneas are iron-poor. In addition, we present NIR observations of five optically gray Trojans, including three objects from the collisionally produced Eurybates family. The five gray Trojans appear featureless in the NIR with no diagnostic absorption features. The NIR spectrum of Eurybates can be best fitted with the spectrum of a CM2 carbonaceous chondrite, which hints that the C-type Eurybates family members may have experienced aqueous alteration.

[1]  David Jewitt,et al.  CCD spectra of asteroids. II - The Trojans as spectral analogs of cometary nuclei , 1990 .

[2]  T. Owen,et al.  Near-Infrared Spectroscopy of Low-Albedo Surfaces of the Solar System: Search for the Spectral Signature of Dark Material , 1998 .

[3]  G. Arnold,et al.  Natural Solid Bitumens as Possible Analogs for Cometary and Asteroid Organics:: 1. Reflectance Spectroscopy of Pure Bitumens , 1998 .

[4]  E. Cloutis,et al.  Near-Infrared Spectroscopy of Primitive Solar System Objects , 1994 .

[5]  D. Tholen,et al.  The nature of c-class asteroids from 3-μm spectrophotometry , 1985 .

[6]  Joshua Patrick Emery,et al.  The surface composition of Trojan asteroids: constraints set by scattering theory , 2004 .

[7]  Paul G. Lucey,et al.  Experimental test of a radiative transfer model of the optical effects of space weathering , 2008 .

[8]  M. Hanner,et al.  Spectrocam-10 Thermal Infrared Observations Of The Dust In Comet C/1995 O1 Hale-Bopp , 1997 .

[9]  N. Pinilla-Alonso,et al.  A peculiar family of Jupiter Trojans: The Eurybates , 2010, 1004.4180.

[10]  Stephan D. Price,et al.  The Supplemental IRAS Minor Planet Survey , 2002 .

[11]  B. Zellner.  44 Nysa - An iron-depleted asteroid , 1975 .

[12]  Jeffrey Edward Moersch,et al.  Thermal emission from particulate surfaces : a comparison of scattering models with measured spectra , 1995 .

[13]  D. Hamilton,et al.  On the Origin of the Trojan Asteroids: Effects of Jupiter's Mass Accretion and Radial Migration , 2000, astro-ph/0007296.

[14]  Elisabetta Dotto,et al.  Optical alteration of complex organics induced by ion-irradiation: 1. Laboratory experiments suggest unusual space weathering trend. , 2004 .

[15]  Carle M. Pieters,et al.  Determining the composition of olivine from reflectance spectroscopy , 1998 .

[16]  J. Bell.  Mineralogical clues to the origins of asteroid dynamical families , 1989 .

[17]  G. Huss,et al.  Presolar diamond, silicon carbide, and graphite in carbonaceous chondrites: implications for thermal processing in the solar nebula , 2003 .

[18]  David Jewitt,et al.  The Albedo Distribution of Jovian Trojan Asteroids , 2003 .

[19]  Richard P. Binzel,et al.  Observed spectral properties of near-Earth objects: results for population distribution, source regions, and space weathering processes , 2004 .

[20]  C. Woodward,et al.  Silicate Mineralogy of the Dust in the Inner Coma of Comet C/1995 01 (Hale-Bopp) Pre- and Postperihelion , 1999 .

[21]  John T. Rayner,et al.  Spextool: A Spectral Extraction Package for SpeX, a 0.8–5.5 Micron Cross‐Dispersed Spectrograph , 2004 .

[22]  Z. Ivezic,et al.  The properties of Jovian Trojan asteroids listed in SDSS Moving Object Catalogue 3 , 2007, astro-ph/0703026.

[23]  Richard P. Binzel,et al.  Asteroid spectroscopy: Progress and perspectives , 1993 .

[24]  Dean C. Hines,et al.  Spitzer Observations of the Dust Coma and Nucleus of 29P/Schwassmann-Wachmann 1 , 2004 .

[25]  Michael J. Gaffey,et al.  Spectral reflectance characteristics of the meteorite classes , 1976 .

[26]  C. Koike,et al.  Optical constants of olivine particles between wavelengths of 7 and 200 μm , 1990 .

[27]  L. A. Rose.  Laboratory simulation of infrared astrophysical features , 1979 .

[28]  Hans Scholl,et al.  Capture of Trojans by a Growing Proto-Jupiter , 1998 .

[29]  Michael E. Zolensky,et al.  The Tagish Lake Meteorite: A Possible Sample from a D-Type Asteroid , 2001, Science.

[30]  M. C. Wyatt,et al.  SPITZER EVIDENCE FOR A LATE-HEAVY BOMBARDMENT AND THE FORMATION OF UREILITES IN η CORVI At ∼1 Gyr , 2011, 1110.4172.

[31]  Elisabetta Dotto,et al.  Ion Irradiation of Frozen Methanol, Methane, and Benzene: Linking to the Colors of Centaurs and Trans-Neptunian Objects , 2006 .

[32]  Adrian J. Brearley,et al.  The Action of Water , 2006 .

[33]  J. Salisbury,et al.  The role of volume scattering in reducing spectral contrast of reststrahlen bands in spectra of powdered minerals , 1992 .

[34]  M. Martino,et al.  Spectroscopic observations of Jupiter Trojans , 2004 .

[35]  R. Gil-Hutton,et al.  Taxonomy of asteroid families among the Jupiter Trojans: comparison between spectroscopic data and the Sloan Digital Sky Survey colors , 2007, 0712.0046.

[36]  J. Bradley,et al.  Combined infrared and analytical electron microscope studies of interplanetary dust particles , 1992 .

[37]  R. Gehrz,et al.  0.7- to 23 μm photometric observations of P/Halley 1986 III and six recent bright comets , 1992 .

[38]  F. De Luise,et al.  Visible spectroscopic and photometric survey of Jupiter Trojans: Final results on dynamical families , 2007, 0704.0350.

[39]  M. Hanner.  The Silicate Material in Comets , 1999 .

[40]  R. Burns.  Intervalence Transitions in Mixed Valence Minerals of Iron and Titanium , 1981 .

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

[42]  E. Tedesco,et al.  Compositional Structure of the Asteroid Belt , 1982, Science.

[43]  D. J. Tholen,et al.  The Eight-Color Asteroid Survey: Results for 589 Minor Planets , 1985 .

[44]  H. Kimura,et al.  Mid-infrared spectra of cometary dust: the evasion of its silicate mineralogy , 2008 .

[45]  R. Brunetto,et al.  Space Weathering in the Main Asteroid Belt: The Big Picture , 2006 .

[46]  Larry A. Lebofsky,et al.  The composition and origin of the C, P, and D asteroids: Water as a tracer of thermal evolution in the outer belt , 1990 .

[47]  Robert K. Vincent,et al.  The behavior of spectral features in the infrared emission from particulate surfaces of various grain sizes , 1968 .

[48]  David Jewitt,et al.  From Kuiper Belt Object to Cometary Nucleus: The Missing Ultrared Matter , 2002 .

[49]  J. Stephens,et al.  Emission and extinction of ground and vapor-condensed silicates from 4 to 14 microns and the 10 micron silicate feature , 1979 .

[50]  Neptune Trojans as a Test Bed for Planet Formation , 2005, astro-ph/0502276.

[51]  Z. Ivezic,et al.  Solar system objects observed in the Sloan Digital Sky Survey commissioning data , 2001 .

[52]  John T. Rayner,et al.  SpeX: A Medium‐Resolution 0.8–5.5 Micron Spectrograph and Imager for the NASA Infrared Telescope Facility , 2003 .

[53]  Paul A. Abell,et al.  Near-IR spectral evidence for the presence of iron-poor orthopyroxenes on the surfaces of six M-type asteroids , 2005 .

[54]  Emmanuel Lellouch,et al.  The Spectrum of Comet Hale-Bopp (C/1995 O1) Observed with the Infrared Space Observatory at 2.9 Astronomical Units from the Sun , 1997, Science.

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

[56]  Richard P. Binzel,et al.  Phase II of the Small Main-Belt Asteroid Spectroscopic Survey: A Feature-Based Taxonomy , 2002 .

[57]  W. Ridley,et al.  Relation of the spectroscopic reflectance of olivine to mineral chemistry and some remote sensing implications , 1987 .

[58]  Fernando Roig,et al.  A Semianalytical Model for the Motion of the Trojan Asteroids: Proper Elements and Families , 2001 .

[59]  Sara Seager,et al.  THEORETICAL SPECTRA OF TERRESTRIAL EXOPLANET SURFACES , 2012, 1204.1544.

[60]  Dale P. Cruikshank,et al.  Thermal emission spectroscopy (5.2–38 μm) of three Trojan asteroids with the Spitzer Space Telescope: Detection of fine-grained silicates , 2006 .

[61]  C. Woodward,et al.  Grain Properties of Comet C/1995 O1 (Hale-Bopp) , 2001 .

[62]  Clark R. Chapman,et al.  S-Type Asteroids, Ordinary Chondrites, and Space Weathering: The Evidence from Galileo's Fly-bys of Gaspra and Ida , 1996 .

[63]  Robert Jedicke,et al.  Evidence for asteroid space weathering from the Sloan Digital Sky Survey , 2005 .

[64]  P G Brown,et al.  The fall, recovery, orbit, and composition of the Tagish Lake meteorite: a new type of carbonaceous chondrite. , 2000, Science.

[65]  F. Marzari,et al.  The surface composition of Jupiter Trojans: Visible and near-infrared survey of dynamical families ☆ , 2006 .

[66]  David Jewitt,et al.  Spectroscopic Search for Water Ice on Jovian Trojan Asteroids , 2006 .

[67]  Roger D. Aines,et al.  Water in minerals? A peak in the infrared , 1984 .

[68]  K. Tsiganis,et al.  Chaotic capture of Jupiter's Trojan asteroids in the early Solar System , 2005, Nature.

[69]  Robert H. Brown,et al.  Constraints on the surface composition of Trojan asteroids from near-infrared (0.8–4.0 μm) spectroscopy , 2003 .

[70]  R. Gil-Hutton,et al.  Surface composition of Hilda asteroids from the analysis of the Sloan Digital Sky Survey colors , 2008 .

[71]  Ludmilla Kolokolova,et al.  Light scattering by cometary dust numerically simulated with aggregate particles consisting of identical spheres , 2006 .