A SPECTROSCOPIC SURVEY OF METALLIC SPECIES ABUNDANCES IN THE LUNAR ATMOSPHERE

Authors
Citation
Bc. Flynn et Sa. Stern, A SPECTROSCOPIC SURVEY OF METALLIC SPECIES ABUNDANCES IN THE LUNAR ATMOSPHERE, Icarus, 124(2), 1996, pp. 530-536
Citations number
20
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Astronomy & Astrophysics
Journal title
IcarusACNP
ISSN journal
0019-1035
Volume
124
Issue
2
Year of publication
1996
Pages
530 - 536
Database
ISI
SICI code
0019-1035(1996)124:2<530:ASSOMS>2.0.ZU;2-Y
Abstract
The first results of an ongoing effort to search for new species in th e lunar atmosphere are presented. The observations in terms of the deg ree to which atomic metal abundances in the lunar atmosphere are stoic hiometric, that is, proportional to surface abundances (as the Na:K ra tio is), are discussed. Na and K are the only atmospheric constituents to have been observed from Earth, but Apollo sample returns establish ed that a variety of species are more abundant in the lunar surface th an either Na or K. Simple stoichiometric arguments (i.e., assuming atm ospheric production proportional to surface abundance) predict that re latively abundant lunar surface constituents such as Si, Al, Ca, Mg, F e, and Ti should be more abundant in the lunar atmosphere than either Na or K. The 2.7-m coude and 2.1-m cassegrain echelle spectrographs at the University of Texas McDonald Observatory were used to investigate this hypothesis by searching for solar resonant scattering lines of n ine metallic species between 3700 and 9700 Angstrom. Spectra were take n 20 arcsec above the apparent subsolar limb of the Moon near quarter phase on 30 July 1994 and 10-12 March 1995. Upper limits were obtained for the first time for the abundant lunar surface species Si, Al, Ca, Fe, and Ti, as well as Ba and the alkalis Li, Rb, and Cs. In the case s of Si, Ca, Fe, and Ti, the derived upper limits are more than an ord er of magnitude lower than the simple stoichiometric model predicts. T he upper limits for Li and Al are less constraining. The Ba, Rb, and C s upper limits lead to the conclusion that those species are not stoic hiometrically overabundant above the detection threshold in the atmosp here. It is concluded that the stoichiometric Na:K ratio is peculiar i n that the mechanism(s) that produce the lunar Na and K atmosphere som ehow favor those atomic species over many more or comparably abundant lunar surface species. (C) 1996 Academic Press, Inc.