

Martian Meteorites Reveal Clues To Processes In Planet's Atmosphere


University of California-San Diego

Media Contact: Kim McDonald, (858) 534-7572,

March 1, 2000


Detailed measurements of sulfur isotopes in five Martian meteorites have enabled researchers at the University of California, San Diego to determine that the abundant sulfur on the surface of Mars is due largely to chemical reactions in the Red Planet's atmosphere that are similar to those that occur in Earth's atmosphere.



"On Earth, if you see a large variation in the sulfur isotope ratio, it generally, though not exclusively, means you've got a biogenic input," said Mark H. Thiemens, professor of chemistry and biochemistry and dean of the Division of Natural Sciences at UCSD. "Organisms are very good at separating isotopes and choosing one over the other. So when you see big changes in isotope ratios, it often means biochemistry."



"Sulfur and a number of other elements are involved in the chemical and physical cycling of elements between oceans, rocks, living organisms and the atmosphere," said Farquhar, the principal author of the study. "We have shown that the sulfur-isotope ratios in Martian meteorites have a component that can only be explained by atmospheric chemical reactions. This provides new insights into the origin of sulfur species found at the Viking and Pathfinder landing sites, and into sulfur mobility within the Martian surface."

"Mars is a nice case study, because it's relatively simple," explained Thiemens. "There's not that much atmosphere, it's photochemical, it couples directly to the surface and it's not complicated by biology or an ocean. Sulfur is a major element and it has a number of isotopes, so it's a very nice probe to understand an entire planetary system."



"When you put them all together to account for the data, it fits," said Thiemens. "Biology can't accommodate what we see, but the photochemistry in the Martian atmosphere does."


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