A rare Martian meteorite recently found in Morocco contains minerals with 10 times more water than previously discovered Mars meteorites, a finding that raises new questions about when and how long the planet most like Earth in the solar system had conditions suitable for life.
The rock is believed to be similar to those studied by NASA's Spirit and Opportunity rovers, which landed on opposite sides of Mars in 2004 to look for signs of past water. Spirit is no longer operational, but in August Opportunity was joined by the new and more sophisticated Curiosity rover, which will be searching for chemistry and environmental conditions necessary to support microbial life.
The meteorite, known as Northwest Africa (NWA) 7034, is the second-oldest of 110 named stones originating from Mars that have been retrieved on Earth. Purchased from a Moroccan meteorite dealer in 2011, the black, baseball-sized stone, which weighs less than 1 pound, is 2.1 billon years old, meaning it formed during what is known as the early Amazonian era in Mars' geologic history.
"It's from a time on Mars that we actually don't know much about," geologist Carl Agee, with the University of New Mexico in Albuquerque, told Discovery News.
The only older Mars meteorite found so far is the 4-billion-year-old Allan Hills 84001 Antarctica stone that was the source of speculation about microfossils in 1996.
Early Mars was believed to be warm and wet, but the planet lost most of its atmosphere and its surface water to become a cold, dry desert that appears today.
"The time from when our meteorite is from is maybe a transitional period in the climate, when Mars was losing its atmosphere, losing its water on the surface," Agee said.
The meteorite is relatively rich in water -- about 6,000 parts per million -- compared with typical Martian meteorites that contain about 200- to 300 parts per million. It is similar to basaltic rocks on Earth that form in volcanic eruptions.
"The fact that this meteorite formed in the presence of water suggests that maybe this water hung around for a while, maybe a bit longer than previously thought. It at least opens our minds to the idea that maybe Mars climate change was more transitional, rather than an abrupt loss of atmosphere and water," Agee said.
Like other Mars meteorites, NWA 7034, nicknamed "Black Beauty," also contains tiny bits of carbon, formed from geologic, not biological activity, said Andrew Steele, who studies Mars meteorites at the Carnegie Institution of Washington DC.
Steele, who also is a member of the Curiosity science team, would like to do more analysis on the meteorite with instruments that are similar to those on the rover.
Scientists don't know why more meteorites like Black Beauty haven't been found on Earth. The period of time from which they originated may be relatively short, or most may not survive the trip through Earth's atmosphere.
"(Mars meteorites) are tough, but by the time they get here they're quite friable and brittle," Steele told Discovery News.
"This one does look completely different," he added. "It's jet black. The others are slightly greenish cast."
After an initial battery of tests revealed the rock's unique nature, meteorite hunters returned to the area where it was found to search for other similar stones, Agee said.
"It took several months to get an idea of what it was," Agee said. "We eventually realized there was no other conclusion but that it was Martian and that it was different from all the other ones."
"If it were similar, we would have known within one day," he added.
Four more pieces, all smaller than the original, have now been found.
The research appears in this week's journal Science.