T152 The Geology of Asteroid 4 Vesta as Seen by Dawn: Results from One Year in Orbit

Tuesday, 6 November 2012
8:00 AM - 12:00 PM
213D

INFLUENCE OF OBSERVATION GEOMETRY AND COMPOSITION ON VIS-NIR SPECTRA OF HED METEORITES

Paper number: T152-13
Program: Technical Sessions
Time: 11:15 AM – 11:30 AM

Authors

Abstract

The Dawn mission has obtained high-resolution spectral data of Vesta using the Visible and Near-Infrared Mapping Spectrometer (VIR) [1]. Earth-based telescopic observations have shown that the spectral properties of HED meteorites are generally similar to Vesta, confirming its composition as a basaltic object [2]. Furthermore subgroups of the HED meteorites have been associated with different regions on the asteroid surface [4]. However, to fully understand the spectral observations of Vesta’s surface, laboratory spectra of a wide range of recovered HED meteorites are needed and attention should be given to critical factors affecting spectra [e.g., 5]. Here we present spectra of 11 HEDs: 8 previously unmeasured meteorites and 3 falls. We focused our analyses on the spectral variability as a function of observation geometry and of composition. The absorption bands at 1 and 2 micrometers are critical indicators of pyroxene compositions, e.g., Fs and Wo abundances [e.g., 6]. We have observed limited variations in the band center positions as a function of phase angle for values <60°. Band depth and spectral slope variations are also limited for low phase angle. Overall, the observed trends in spectral parameter variability agree with previous analyses of a HED sample and asteroids [e.g., 4]. However our suite of HEDs presents some variations from the systematic trends both at low and high phase angle. Compositional influences on spectra will be discussed with respect to the pyroxene compositions, the presence of one or two pyroxene phases, plagioclase, and opaque minerals abundances. Because of its relevance for the magmatic history of Vesta, we will also discuss the influence of olivine abundance on the spectral properties.

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[2] McCord, et al.: (1970) Science, Vol 168, Issue 3938, pp. 1445-1447.

[3] Burbine T. H., et al. : (2007) #2117, 38th Lunar and Planetary Science Conference.

[4] Binzel, R.P., et al : (1997) Icarus 128, pp. 95-103

[5] Beck, P., et al. : (2011) Icarus 216, pp.560-571.

[6] Gaffey, M. J., et al. :(2002) in Asteroids III, University of Arizona Press, Tucson.

[7] Reddy, V., et al., (2012) Icarus 217, pp. 153-168