Department of Climate and Space Sciences and Engineering in the College of Engineering at the University of Michigan

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Curiosity confirms origins of Martian meteorites

Posted: October 22, 2013

Curiosity confirms origins of Martian meteorites

A new measurement from the Curiosity rover provides the most definitive evidence yet of the origins of Mars meteorites while at the same time providing a way to rule out Martian origins of other meteorites.

“We really nailed it,” says Professor Sushil Atreya, who is a co-investigator for the SAM (Sample Analysis at Mars) instrument on the Curiosity rover.

SAM accomplished the new measurement – a high-precision count of two forms of argon gas—Argon-36 and Argon-38.

These lighter and heavier forms, or isotopes, of argon exist naturally throughout the solar system. But on Mars the ratio of light to heavy argon is skewed because a lot of that planet’s original atmosphere was lost to space, with the lighter form of argon being taken away more readily because it rises to the top of the atmosphere more easily and requires less energy to escape. That’s left the Martian atmosphere relatively enriched in the heavier Argon-38.

Years of past analyses by Earth-bound scientists of gas bubbles trapped inside Martian meteorites had already narrowed the Martian argon ratio to between 3.6 and 4.5 (that is 3.6 to 4.5 atoms of Argon-36 to every one Argon-38) with the supposed Martian “atmospheric” value near four. Measurements by NASA’s Viking landers in the 1970’s put the Martian atmospheric ratio in the range of four to seven. The new SAM direct measurement on Mars now pins down the correct argon ratio at 4.2.

“This direct reading from Mars settles the case with all Martian meteorites,” Atreya says.

To read the full story, please visit the AGU website.

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