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Hydrogen and major element concentrations on 433 Eros: Evidence for an L‐ or LL ‐chondrite‐like surface composition
Author(s) -
Peplowski Patrick N.,
Bazell David,
Evans Larry G.,
Goldsten John O.,
Lawrence David J.,
Nittler Larry R.
Publication year - 2015
Publication title -
meteoritics and planetary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.09
H-Index - 100
eISSN - 1945-5100
pISSN - 1086-9379
DOI - 10.1111/maps.12434
Subject(s) - chondrite , regolith , ordinary chondrite , meteorite , asteroid , space weathering , geology , hydrogen , carbonaceous chondrite , astrobiology , mineralogy , chemical composition , geochemistry , chemistry , physics , organic chemistry
A reanalysis of NEAR X‐ray/gamma‐ray spectrometer ( XGRS ) data provides robust evidence that the elemental composition of the near‐Earth asteroid 433 Eros is consistent with the L and LL ordinary chondrites. These results facilitated the use of the gamma‐ray measurements to produce the first in situ measurement of hydrogen concentrations on an asteroid. The measured value, 1100 − 700 + 1600 ppm, is consistent with hydrogen concentrations measured in L and LL chondrite meteorite falls. Gamma‐ray derived abundances of hydrogen and potassium show no evidence for depletion of volatiles relative to ordinary chondrites, suggesting that the sulfur depletion observed in X‐ray data is a surficial effect, consistent with a space‐weathering origin. The newfound agreement between the X‐ray, gamma‐ray, and spectral data suggests that the NEAR landing site, a ponded regolith deposit, has an elemental composition that is indistinguishable from the mean surface. This observation argues against a pond formation process that segregates metals from silicates, and instead suggests that the differences observed in reflectance spectra between the ponds and bulk Eros are due to grain size differences resulting from granular sorting of ponded material.