The US space agency's (Nasa) robotic Mars rover Opportunity has discovered the first meteorite ever seen on the surface of the Red Planet.
Only 2% of meteorites on Earth are so metal-rich
Earlier this year, mission scientists spotted the pitted rock near to the remains of the rover's heat shield, which is lying on Meridiani Planum.
Analysis showed it was made of iron and nickel, confirming it was not Martian, and instead fell from space.
Only 2% of meteorites on Earth are this metal-rich; most are rockier.
"This is a huge surprise, though maybe it shouldn't have been," said Professor Steve Squyres, of Cornell University in Ithaca, US, the principal investigator for the rover science payload.
The rock was identified as being metal-rich in data from the rover's Mini-Thermal Emission Spectrometer (Mini-Tes) instrument.
Over the weekend, Opportunity drove to the rock, extended its instrument arm and used its Mössbauer and alpha particle X-ray spectrometers to confirm it was not Martian.
The meteorite sits near debris from Opportunity's heat shield, which protected the rover's entry vehicle during its plunge into the Martian atmosphere nearly one year ago.
It now lies on Meridiani Planum, the same cratered plain Opportunity landed on.
"I never thought we would get to use our instruments on a rock from someplace other than Mars," said Professor Squyres.
"Think about where an iron meteorite comes from: a destroyed planet or planetesimal that was big enough to differentiate into a metallic core and a rocky mantle."
If researchers can find more meteorites, they may learn more about surface processes at Meridiani.
The numbers of exposed meteorites could be an indication of whether the Meridiani plain is gradually eroding away or being built up.