Red Planet meteorites found: History of water on Mars revealed

SCIENCE: The meteorite from Mars has a history of contact with water, possibly from volcanic activity on the Red Planet that melted ice 700 million years ago. The discovery helps unravel the story of an 800-gram (1.8-pound) meteorite that has been a mystery for nearly 100 years, found in 1931 in a desk drawer at Purdue University in Indiana, US.

An international team of scientists led by Purdue’s Marisa Tremblay has the answer. By dating the minerals altered by water in the Lafayette meteorite, they zeroed in on a date of 742 million years ago. However, according to Martian climatology, the Red Planet’s liquid water disappeared about 3 billion years ago. So where did the water come from 742 million years ago? The meteorite was named Lafayette, after the city where Purdue University is located. How it got into that drawer was unknown, but it was known that it originally came from Mars and had once come into contact with liquid water there. The question was, how long ago did its wet experience occur?

“We don’t think there was abundant liquid water on the surface of Mars at this time,” Tremblay said in a statement. “Instead, we think the water came from the melting of nearby sub-surface ice called permafrost, and that the permafrost melting was caused by magmatic activity that still occurs periodically on Mars today.”

The Lafayette meteorite is a type of Martian meteorite known as a nakhlite. Made of igneous, i.e., volcanic rocks, they likely originated from a crater on basaltic lava planes near the extinct Elysium Mons volcano. Therefore, dating the history of nakhlite on Mars is a major objective of planetary scientists. When the Lafayette meteorite (and possibly other nakhlites as well) collided with Mars and spun off into space, they were exposed to cosmic rays irradiated by the meteorite, producing isotopes that have been dated to about 11 million years ago, the same age as craters near Elysium Mons.