Photometric, spectral phase and temperature effects on 4 Vesta and HED meteorites: Implications for the Dawn mission

Vishnu Reddy, Juan A. Sanchez, Andreas Nathues, Nicholas A. Moskovitz, Jian Yang Li, Edward A. Cloutis, Ken Archer, Roy A. Tucker, Michael J. Gaffey, J. Paul Mann, Holger Sierks, Ulrich Schade

Research output: Contribution to journalArticlepeer-review

69 Scopus citations


Phase angle and temperature are two important parameters that affect the photometric and spectral behavior of planetary surfaces in telescopic and spacecraft data. We have derived photometric and spectral phase functions for the Asteroid 4 Vesta, the first target of the Dawn mission, using ground-based telescopes operating at visible and near-infrared wavelengths (0.4-2.5μm). Photometric lightcurve observations of Vesta were conducted on 15 nights at a phase angle range of 3.8-25.7° using duplicates of the seven narrowband Dawn Framing Camera filters (0.4-1.0μm). Rotationally resolved visible (0.4-0.7μm) and near-IR spectral observations (0.7-2.5μm) were obtained on four nights over a similar phase angle range. Our Vesta photometric observations suggest the phase slope is between 0.019 and 0.029. mag/deg. The G parameter ranges from 0.22 to 0.37 consistent with previous results (e.g., Lagerkvist, C.-I., Magnusson, P., Williams, I.P., Buontempo, M.E., Argyle, R.W., Morrison, L.V. [1992]. Astron. Astrophys. Suppl. Ser. 94, 43-71; Piironen, J., Magnusson, P., Lagerkvist, C.-I., Williams, I.P., Buontempo, M.E., Morrison, L.V. [1997]. Astron. Astrophys. Suppl. Ser. 121, 489-497; Hasegawa, S. et al. [2009]. Lunar Planet. Sci. 40. ID 1503) within the uncertainty. We found that in the phase angle range of 0°<.α≤. 25° for every 10° increase in phase angle Vesta's visible slope (0.5-0.7μm) increases 20%, Band I and Band II depths increase 2.35% and 1.5% respectively, and the BAR value increase 0.30. Phase angle spectral measurements of the eucrite Moama in the lab show a decrease in Band I and Band II depths and BAR from the lowest phase angle 13° to 30°, followed by possible small increases up to 90°, and then a dramatic drop between 90° and 120° phase angle. Temperature-induced spectral effects shift the Band I and II centers of the pyroxene bands to longer wavelengths with increasing temperature. We have derived new correction equations using a temperature series (80-400. K) of HED meteorite spectra that will enable interpretation of telescopic and spacecraft spectral data using laboratory calibrations at room temperature (300. K).

Original languageEnglish (US)
Pages (from-to)153-168
Number of pages16
Issue number1
StatePublished - Jan 2012
Externally publishedYes


  • Asteroid Vesta
  • Asteroids, Composition
  • Infrared observations
  • Photometry
  • Spectroscopy

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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