Of the more than 74,000 known meteorites– rocks that fall to Earth from asteroids or planets colliding together – only 385 or so stones came from the planet Mars.
It’s not that hard for scientists to work out that these meteorites come from Mars. Various landers and rovers have been exploring Mars’ surface for decades. Some of the early missions – the Viking landers– had the equipment to measure the composition of the planet’s atmosphere. Scientists have shown that you can see this unique Martian atmospheric composition reflected in some of these meteorites.
Mars also has unique oxygen. Everything on Earth, including humans and the air we breathe, is made up of a specific composition of the three isotopes of the element oxygen: oxygen-16, oxygen-17 and oxygen-18. But Mars has an entirely different composition – it’s like a geochemical fingerprint for being Martian.
The Martian meteorites found on Earth give geologists like me hints about the makeup of the red planet and its history of volcanic activity. They allow us to study Mars without sending a spacecraft 140 million miles away.
