Until 2005, all the meteorites ever studied had been found on Earth (not counting two on the Moon). We hadn’t really been anywhere else. But a year after the Opportunity rover landed on Mars in 2004, it discovered the first meteorite to be found on another planet. The discovery was an accident; the rover was looking for the heat shield that had been ejected during its landing. Sitting next to the shield was large, pocked ball of iron—theHeat Shield Rock.
Since the rover wasn’t equipped to drill into something made of almost pure iron, we haven’t been able to study it much. But one thing is certain—due to the way it survived its fall intact, it must have been traveling fairly slowly. To do that, Mars must have had amuch thicker atmospherewhen it fell, an atmosphere that contained water. This brings us we closer to figuring out the timeline of the changes in Mars’s atmosphere, something we’ve never really been able to do. And all it took was a chunk of rock.