A team of scientists has established a whole new class of meteorites that seems to have come from Mars' crust, based on a rare sample from 2.1 billion years ago.
The newly analyzed meteorite has more water than any other Martian meteorite that we know of, by a magnitude of 10, said Carl Agee, lead study author and director of the Institute of Meteoritics at the University of New Mexico. Agee and colleagues published their analysis of the meteorite in the journal Science Express.
"There are thousands and thousands of meteorites, and so far this is the only one like it," Agee said.
This is a volcanic rock that was probably part of an eruption, and interacted with water to the extent that some water got incorporated into the structure of the minerals, Agee said. "That's why we're able to see it after a couple of billion years," he said.
The precise source of the water in the meteorite is unknown. It could have come from a lake or stream, or ground water that a volcano intruded into, Agee said. Alternatively, the water could have come from frozen Martian tundra that melted when hot volcanic material moved through it.
"We do know that there was a significant amount [of water] available," he said.
Agee and colleagues were able to extract water from the meteorite by putting it into a vacuum-sealed tube and heating it up. Using a mass spectrometer, they were able to determine that the gas released from the heated meteorite was water vapor.
"That vapor is true Martian water that is, sort of like, being awakened" after many years, he said. "We're pulling it out of the rock."
Agee's meteorite is similar to the type of rocks that NASA spacecraft have found on the surface of Mars in terms of its chemical composition. This is the first meteorite that's a good match to those rocks on Mars today.
The meteorite's age also makes it unique, Agee said. It from 2.1 billion years ago, making it the second-oldest sample that we have. The oldest is the Alan Hills meteorite, discovered in Antarctica in 1984, which is 4.5 billion years old. All other samples have been much younger.
Right now, Mars is cold and dry, inhospitable for life, Agee said. But many scientists believe the environment used to be warm and wet and that somewhere in its history the planet lost its atmosphere and surface water. When and how that happened are big mysteries.
"This meteorite is a sample from that transitional period, perhaps," Agee said. "Because of the water that's present in it, it may be giving us a glimpse of what the surface conditions were like, as well."
The rare Mars rocks came from Morocco. There are nomads in that country who make a living by scouring the Sahara Desert for the dark, black rocks that have fallen from space, Agee explains. They bring these meteorites into towns and sell them to a dealer. Then the dealer sells them internationally to collectors, museums and scientists.
When Agee realized how rare and important his first sample was, he wanted to know if there were more. The meteorite hunters have since recovered a few more pieces.
The biggest piece of this Martian meteorite fits into the palm of your hand and weighs 320 grams (about 11 ounces), Agee said. There are two samples in his lab and two more in Paris.
"It's going to be real interesting to see if there are more that are recovered," he said. "But I think that this particular type is going to be extraordinarily rare."