[Previous] | [Session 2] | [Next]
S.W. Squyres (Cornell U.), J.I. Trombka, J. Brueckner, W.V. Boynton, R.C. Reedy, P. Gorenstein, L.G. Evans, J.R. Arnold, R.D. Starr, L.R. Nittler, T.J. McCoy, I. Mikheeva, R.L. McNutt, T.P. McClanahan, E. McCartney, J.O. Goldsten, R.E. Gold, S.R. Floyd, P.E. Clark, T.H. Burbine, J.S. Banghoo, S.H. Bailey, M.E. Murphy ()
From 2 May to 25 July 2000, while the NEAR Shoemaker spacecraft was in 50- and 35-km orbits around Eros, more than 80 M-class and higher solar flares occurred, of which about 30 produced measurable fluorescence from the asteroid. We report the major element composition (Mg, Al, Si, S, Ca, Fe) for regions of the asteroid observed during both flares and quiet Sun conditions. The quiet Sun spectra are concentrated around the craters Psyche and Himeros, while the best flare data are centered on Himeros and just outside and to the west of Psyche. Low aluminum abundances for all these regions argue strongly against global differentiation of Eros. In contrast to the aluminum-rich compositions found in the howardite-eucrite-diogeniate suite, Eros is compositionally similar to the unfractionated H, L and LL ordinary chondrites. Fe is detectable only in flare spectra. Fe/Si ratios bracket the ordinary chondrites, as well as some meteorites that have experienced limited partial melting (e.g., winonaites, acapulcoites). Mg/Si ratios overlap ordinary chondrites. Ca/Si ratios are identical, within error, to ordinary chondrites, but sulfur is markedly depleted relative to ordinary chondrites. The sulfur depletion could result from limited partial melting or impact volatilization. Further x-ray measurements should allow us to search for spatial heterogeneity in composition. Gamma-ray measurements, which require significantly longer integration times, will yield information about some other elements, and also will allow sampling to depths significantly greater than sampled with x rays.