NEAR infrared spectrometer photometry of asteroid 433 Eros

Beth E. Clark, P. Helfenstein, J. F. Bell, C. Peterson, J. Veverka, N. I. Izenberg, D. Domingue, D. Wellnitz, Lucy McFadden

Research output: Contribution to journalArticlepeer-review

102 Scopus citations

Abstract

We present near-infrared spectrometer (NIS) observations (0.8 to 2.4 μm) of the S-type asteroid 433 Eros obtained by the NEAR Shoemaker spacecraft and report results of our Hapke photometric model analysis of data obtained at phase angles ranging from 1.2° to 111.0° and at spatial resolutions of 1.25 × 2.5 to 2.75 × 5.5 km/spectrum. Our Hapke model fits successfully to the NEAR spectroscopic data for systematic color variations that accompany changing viewing and illumination geometry. Model parameters imply a geometric albedo at 0.946 μm of 0.27 ± 0.04, which corresponds to a geometric albedo at 0.550 μm of 0.25 ± 0.05. We find that Eros exhibits phase reddening of up to 10% across the phase angle range of 0-100°. We observe a 10% increase in the 1-μm band depth at high phase angles. In contrast, we observe only a 5% increase in continuum slope from 1.486 to 2.363 μm and essentially no difference in the 2-μm band depth at higher phase angles. These contrasting phase effects imply that there are phase-dependent differences in the parametric measurements of 1- and 2-μm band areas, and in their ratio. The Hapke model fits suggest that Eros exhibits a weaker opposition surge than either 951 Gaspra or 243 Ida (the only other S-type asteroids for which we possess disk-resolved photometric observations). On average, we find that Eros at 0.946 μm has a higher geometric albedo and a higher single-scatter albedo than Gaspra or Ida at 0.56 μm; however, Eros's single-particle phase function asymmetry and average surface macroscopic roughness parameters are intermediate between Gaspra and Ida. Only two of the five Hapke model parameters exhibit a notable wavelength dependence: (1) The single-scatter albedo mimics the spectrum of Eros, and (2) there is a decrease in angular width of the opposition surge with increasing wavelength from 0.8 to 1.7 μm. Such opposition surge behavior is not adequately modeled with our shadow-hiding Hapke model, consistent with coherent backscattering phenomena near zero phase.

Original languageEnglish (US)
Pages (from-to)189-204
Number of pages16
JournalIcarus
Volume155
Issue number1
DOIs
StatePublished - Jan 1 2002
Externally publishedYes

Keywords

  • 433 Eros
  • Asteroid
  • Asteroid surfaces
  • NEAR
  • Photometry
  • Spectrophotometry

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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