Hiding the atmosphere of Mars.

Hiding the atmosphere of Mars 

The major constituent of the Martian atmosphere is carbon dioxide, and scientists have assumed that there ought to be something in the "soil" and polar caps that serves as a buffer, or reservoir, to maintain the atmospheric supply. Yet the leading candidate, carbonate rock, has unaccountably remained elusive. Now researchers have discovered a mineral on Mars that may fill the bill.

Called scapolite, it is somewhat rare on Earth, where it usually forms by heat-processing of carbonate rocks, often at points of contact with volcanic rocks. It has also been found in basaltic igneous rocks that have been altered by fluids rich in carbon dioxide.

Its presence on Mars was detected by Roger N. Clark and Gregg A. Swayze of the U.S. Geological Survey (USGS) in Golden, Colo., together with other colleagues. They found it during observations in August and September with a new spectrometer mounted to NASA's 3-meter infrared telescope on Mauna Kea, Hawaii. The researchers suggest that the precision of the near-infrared spectra yielding the new find may have been aided by the fact that Mars was closer to Earth than it had been in nearly 20 years.

In order to identify minerals with spectral absorption bands that might match the Martian data, the scientists examined spectra of hundreds of minerals, consulting the USGS digital spectral database. The Mars data revealed five bands that matched the spectrum of scapolite. The researchers suggest that one possible source of scapolite on Mars could have been carbon dioxide combined with calcium plagioclase, probably produced by volcanoes in the ancient Martian past.