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Photometric Properties of Vesta

Published online by Cambridge University Press:  05 March 2015

Jian-Yang Li
Affiliation:
Planetary Science Institute email: [email protected]
L. Jorda
Affiliation:
Laboratoire d'Astrophysique de Marseille
H. U. Keller
Affiliation:
University Braunschweig, IGEP
N. Mastrodemos
Affiliation:
Jet Propulsion Laboratory, California Institute of Technology
S. Mottola
Affiliation:
DLR, Inst. of Planetary Research
A. Nathues
Affiliation:
Institute for Solar System Research, Max-Planck
C. Pieters
Affiliation:
Brown University, Planetary Geosciences Group
V. Reddy
Affiliation:
Institute for Solar System Research, Max-Planck
C. A. Raymond
Affiliation:
Jet Propulsion Laboratory, California Institute of Technology
T. Roatsch
Affiliation:
DLR, Inst. of Planetary Research
C. T. Russell
Affiliation:
UCLA, Institute of Geophysics
B. J. Buratti
Affiliation:
Jet Propulsion Laboratory, California Institute of Technology
S. E. Schroder
Affiliation:
Institute for Solar System Research, Max-Planck
M. V. Sykes
Affiliation:
Planetary Science Institute email: [email protected]
T. Titus
Affiliation:
US Geological Survey, Astrogeology Science Center
F. Capaccioni
Affiliation:
INAF, Istituto di Astrofisica Spaziale e Fisica Cosmica
M. T. Capria
Affiliation:
INAF, Istituto di Astrofisica Spaziale e Fisica Cosmica
L. Le Corre
Affiliation:
Institute for Solar System Research, Max-Planck
B. W. Denevi
Affiliation:
Johns Hopkins University Applied Physics Laboratory
M. De Sanctis
Affiliation:
INAF, Istituto di Astrofisica Spaziale e Fisica Cosmica
M. Hoffmann
Affiliation:
Institute for Solar System Research, Max-Planck
M. D. Hicks
Affiliation:
Jet Propulsion Laboratory, California Institute of Technology
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Abstract

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The Dawn spacecraft orbited Asteroid (4) Vesta for a year, and returned disk-resolved images and spectra covering visible and near-infrared wavelengths at scales as high as 20 m/pix. The visible geometric albedo of Vesta is ~ 0.36. The disk-integrated phase function of Vesta in the visible wavelengths derived from Dawn approach data, previous ground-based observations, and Rosetta OSIRIS observations is consistent with an IAU H-G phase law with H=3.2 mag and G=0.28. Hapke's modeling yields a disk-averaged single-scattering albedo of 0.50, an asymmetry factor of -0.25, and a roughness parameter of ~20 deg at 700 nm wavelength. Vesta's surface displays the largest albedo variations observed so far on asteroids, ranging from ~0.10 to ~0.76 in geometric albedo in the visible wavelengths. The phase function of Vesta displays obvious systematic variations with respect to wavelength, with steeper slopes within the 1- and 2-micron pyroxene bands, consistent with previous ground-based observations and laboratory measurement of HED meteorites showing deeper bands at higher phase angles. The relatively high albedo of Vesta suggests significant contribution of multiple scattering. The non-linear effect of multiple scattering and the possible systematic variations of phase function with albedo across the surface of Vesta may invalidate the traditional algorithm of applying photometric correction on airless planetary surfaces.

Type
Contributed Papers
Copyright
Copyright © International Astronomical Union 2015