Origins of Martian Meteorites Revealed by NASA's Curiosity Rover

New analysis of of Martian rock samples by NASA's Curiosity rover have allowed scientists to definitively say that some meteorites found on Earth are indeed from Mars, while also providing that data to rule out the Martian origins of other meteorites.

The revelation comes from the Curiosity's high-precision analysis of two forms of argon gas: Argon-36 and Argon-38. Both isotopes of argon, Ar-38 and Ar-38 exist naturally throughout the solar system. But on Mars, the ratio of light to heavy argon is skewed, with more of the heavier Ar-38 present.

What the Curiosity accomplished was to pin down the precise ratio of the two argon isotopes, a find that will help define the exact argon signature contained within Martian rocks.

"We really nailed it," said lead study author Sushil Atreya of the University of Michigan, Ann Arbor, who published the work in the journal Geophysical Research Letters. "This direct reading from Mars settles the case with all Martian meteorites," he said.

The find was also welcomed by scientists because it helps paint a clearer picture of what Mars was like in its days as a wetter, warmer world billions of years ago. A better understanding of how that transition happened could lead to new insights on how the same event may happen here on Earth.

Argon's position as a noble gas -- meaning that it does not react with other elements -- also provides scientists with a more straightforward tracer of the history of the Martian atmosphere.

"Other isotopes measured by [the Sample Analysis at Mars (SAM) instrument] on Curiosity also support the loss of atmosphere, but none so directly as argon," said Atreya. "Argon is the clearest signature of atmospheric loss because it's chemically inert and does not interact or exchange with the Martian surface or the interior. This was a key measurement that we wanted to carry out on SAM."