A Martian meteorite

At first, NWA 7034 appeared to be very un-Mars-like. Laser fluorination revealed that its ratio of heavier-to-lighter oxygen isotopes, usually a handy fingerprint of a meteorite's origins, didn't match any of the Mars meteorites described in the scientific literature. Those meteorites seemed to come from volcanic deposits formed deep inside Mars, because their chemical makeup was different from the data sent back by rovers and spacecraft examining the Red Planet's surface.

If Agee's team had looked no further, the space rock might have been classified as an oddball piece of asteroid and quite possibly forgotten. But rubidium-strontium dating indicated that NWA 7034 was just 2.1 billion years old — far too young to come from an asteroid.

Meteorites that come from asteroids are typically more than 4 billion years old, since these small rocky bodies quickly cooled after the solar system's formation. Planets, on the other hand, were volcanically active for much longer, and many of their rocks formed much later. Black Beauty must have come from a planet, the team members concluded.

The meteorite had too much iron to have come from Mercury and it had too many traces of water to have come from Venus. But when they analyzed minerals called pyroxenes, they found that the ratio of iron to manganese did match those of other Martian meteorites.

This meteorite has been wrongly described in some writeups as the first one from Mars.  It's the first one that originated from the crust of Mars.

It's unclear why most Martian meteorites have come from the planet's interior, he added, though it may be that crustal rock is more fragile and less likely to survive a journey through space or entry into Earth's atmosphere.

Text from the Los Angeles Times.  Photo credit (Carl Agee / University of New Mexico / January 3, 2013).