Thursday, October 17, 2013
Some meteorites that drop in on Earth come from Mars.
We have suspected this for years, but this week, NASA's Curiosity rover confirmed their origin.
Using Sample Analysis at Mars (SAM) instrument — a highly sophisticated onboard chemistry lab that can conduct hundreds of the same experiments we do on Earth — Curiosity rover found two forms of argon, a noble gas that doesn't react to other compounds. This is an important gas because it tells the straightforward history of Mars, which was once a wet planet similar to Earth.
While argon exists throughout our solar system, on Mars, the ratio of heavy to light argon is skewed due to the loss of its atmosphere over billions of years. This fundamentally changed it into the cold, desert-like planet that exists today.
Modern Mars is filled with the heavy form, Argon 38. The lighter form, Argon 36, rose to the top where it then easily escaped. In a sense, Curiosity uncovered the planet's hidden signature by pinning down the ratio of these two forms at 4:2. To put that into context, NASA's Viking landers estimated the planet's atmospheric value to be in the range of 4:7.
"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.br />
Out of the tens of thousands of known meteorites to slam into Earth, less than 50 have been identified with Mars origins.
The study appears in Geophysical Research Letters, a journal of the American Geophysical Union.