A fist-sized meteorite nicknamed Black Beauty could provide vital clues about the evolution of Mars from the warm and wet place it once was to its current cold and dry state, Nasa says.
Discovered in Morocco's Sahara Desert in 2011, the 320g space rock contains 10 times more water than other Martian meteorites.
It could be the first to have originated from the planet's surface or crust.
After more than a year of study, a team of US scientists determined the meteorite formed 2.1 billion years ago during the beginning of the most recent geologic period on Mars, known as the Amazonian, Nasa said on Thursday.
The abundance of water molecules in the meteorite - about 6000 parts per million - suggests water activity on the Martian surface when it was formed.
It is generally thought Mars had abundant water early in its existence - scientists ponder if life once existed there - but the nature of its evolution to a cold and dry place remains a mystery.
"Many scientists think that Mars was warm and wet in its early history but the planet's climate changed over time," lead scientist Carl Agee, whose study was published in Science Express, told Space.com.
Known technically as NWA (Northwest Africa) 7034, Black Beauty comprises fragments of basalt, a rock that forms from rapidly cooled lava.
"Perhaps most exciting is that the high water content could mean there was an interaction of the rocks with surface water either from volcanic magma, or from fluids from impacting comets during that time," co-author Andrew Steele said.
"It is the richest Martian meteorite geochemically and further analyses are bound to unleash more surprises."
Unlike most Martian meteorites, it's thought to be from the planet's surface because its chemistry matches surface rocks Nasa has studied remotely via Mars rovers and orbiting satellites.
More than 100 Martian meteorites have been discovered on Earth to date but most originate from three larger meteorites: Shergotty, Nakhla, and Chassigny.
NWA 7034 has unique characteristics and it took scientists several months to ascertain it came from Mars and not another planet or an asteroid belt.
Agee said Black Beauty gives scientists a glimpse of Mars' ancient surface and environmental conditions that no other meteorite has ever offered.
"This Martian meteorite has everything in its composition that you'd want in order to further our understanding of the Red Planet," he said.