Nature 314, 248 - 250 (21 March 1985); doi:10.1038/314248a0

Martian atmospheric carbon dioxide and weathering products in SNC meteorites

R. H. Carr, M. M. Grady, I. P. Wright & C. T. Pillinger

Planetary Sciences Unit, Department of Earth Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK

SNC meteorites—four shergottites, three nakhlites and Chassigny—are postulated to have originated on Mars¹. Their late crystallization ages (<1,300 Myr compared with 4,600 Myr for other igneous meteorites) and the presence, in shock-produced glass in EETA79001, of noble gas² and nitrogen³ components resembling the martian atmosphere provide evidence for such a provenance. If this interpretation is correct then carbon dioxide, by far the most abundant constituent of the martian atmosphere⁴, should also be present. The stepped combustions described here show that most of the carbon present in the samples can be ascribed to terrestrial contamination. EETA79001, however, contains 4.6 p.p.m. of an isotopically distinct component enriched in ¹³C ( ¹³C = +36), whereas high-temperature carbon of inferred igneous origin in this meteorite and other SNCs has a ¹³C value of about -30. The ¹²C/¹³C ratio of the isotopically heavy component is within the error limits of Viking measurements⁴ in the martian atmosphere and, thus, strengthens the case for a planetary origin. Another carbon-containing species, believed to be carbonate, has been found in Nakhla ( ¹³C = between +12 and +24) and may be a product of atmospheric weathering on Mars.

References

1.	Wood, C. A. & Ashwal, L. D. Proc. Lunar planet. Sci. 12B, 1359−1375 (1981).
2.	Bogard, D. D. & Johnson, P. Science 221, 651−654 (1983). | ISI | ChemPort |
3.	Becker, R. H. & Pepin, R. O. Earth planet. Sci. Lett. 69, 225−242 (1984). | Article | ISI | ChemPort |
4.	Owen, T. et al. J. geophys. Res. 82, 4635−4639 (1977). | ChemPort |
5.	Swart, P. K., Grady, M. M. & Pillinger, C. T. Meteoritics 18, 137−154 (1983). | ISI | ChemPort |
6.	Gibson, E. K. Jr & Bogard, D. D. Meteoritics 13, 277−289 (1978).
7.	Gibson, E. K. Jr & Kotra, R. K. Meteoritics 17, 220−221 (1979).
8.	DesMarais, D. J. Proc. 9th Lunar planet. Sci. Conf. 2451−2467 (1978). | ChemPort |
9.	Bogard, D. D. Abstr. 47th met. Soc. Meet., Albuquerque, J-5 (1984).
10.	Carr, R. H., Wright, I. P. & Pillinger, C. T. J. geophys. Res. (in the press).
11.	Fallick, A. E. et al. Abstr. 14th Lunar planet. Sci. Conf. 183−184 (1983).
12.	Deines, P. Geochim. cosmochim. Acta 32, 613−625 (1968). | Article | ISI | ChemPort |
13.	Gooding, J. L. Icarus 33, 483−513 (1978). | Article | ISI | ChemPort |
14.	Bunch, T. E. & Reid, A. M. Abstr. 37th met. Soc. Meet., Los Angeles (1974).
15.	Kotra, R. K., Gibson, E. K. Jr & Urbancic, M. A. Icarus 51, 593−605 (1982). | Article | ISI | ChemPort |