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November 3,a chhuak Astronomy magazine a chhuak a nia,ka leh sual palh hlauin a ngai ngaiin ka lo dah lut tawp mai,felhlello tur ah ka ngai phawt(By Jet Propulsion Laboratory, Pasadena, California, NASA Headquarters, Washington, D.C. — Published: November 3, 2011).

Tun hnai mai a NASA in a zir dan report ah chuan Mars ah hian Nunna a aawm theih rinna chu evidence tha tak an nei ta.

A new interpretation of years of mineral-mapping data, from more than 350 sites on Mars examined by European and NASA orbiters, suggests martian environments with abundant liquid water on the surface existed only during short episodes. These episodes occurred toward the end of hundreds of millions of years during which warm water interacted with subsurface rocks. This has implications about whether life existed on Mars and how its atmosphere has changed.

“The types of clay minerals that formed in the shallow subsurface are all over Mars,” said John Mustard from Brown University in Providence, Rhode Island. “The types that formed on the surface are found at very limited locations and are quite rare.”

Clay minerals kum 2005 a an hmuhchhuah tang tawh khan Mars hian boruak lum tak atang hnawnglam a pan tih hriatchhuah a ni a.Chumi lo thleng meuh tur erawh chuan era thui tam tak a mamawh tih chu a hriat mai,chuvangin Mars leilung pawh hian atmosphere chhah lemlo tak,hnawnglam chu a pai tam zawk a ni.

“If surface habitats were short-term, that doesn’t mean we should be glum about prospects for life on Mars, but it says something about what type of environment we might want to look in,” said Bethany Ehlmann from the California Institute of Technology and NASA’s Jet Propulsion Laboratory in Pasadena, California. “The most stable Mars habitats over long durations appear to have been in the subsurface. On Earth, underground geothermal environments have active ecosystems.”

The discovery of clay minerals by the OMEGA spectrometer on the European Space Agency’s Mars Express orbiter added to earlier evidence of liquid martian water. Clays form from the interaction of water with rock. Different types of clay minerals result from different types of wet conditions.

During the past five years, researchers used OMEGA and NASA’s Compact Reconnaissance Imaging Spectrometer (CRISM) instrument on the Mars Reconnaissance Orbiter to identify clay minerals at thousands of locations on Mars. Clay minerals that form where the ratio of water interacting with rock is small generally retain the same chemical elements as the original volcanic rocks later altered by the water.

The study interprets this to be the case for most terrains on Mars with iron and magnesium clays. In contrast, surface environments with higher ratios of water to rock can alter rocks further. Soluble elements are carried off by water, and different aluminum-rich clays form.

Another clue is detection of a mineral called prehnite. It forms at temperatures above about 400° Fahrenheit (200° Celsius). These temperatures are typical of underground hydrothermal environments rather than surface waters.

“Our interpretation is a shift from thinking that the warm, wet environment was mostly at the surface to thinking it was mostly in the subsurface, with limited exceptions,” said Scott Murchie from Johns Hopkins University in Laurel, Maryland.

One of the exceptions may be Gale Crater, the site targeted by NASA’s Mars Science Laboratory mission. Launching this year, the Curiosity rover will land and investigate layers that contain clay and sulfate minerals.

NASA’s Mars Atmosphere and Volatile Evolution Mission (MAVEN), in development for a 2013 launch, may provide evidence for or against this new interpretation of the Red Planet’s environmental history. The report predicts MAVEN findings consistent with the atmosphere not having been thick enough to provide warm, wet surface conditions for a prolonged period.

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