I look at rocks on Mars for a living—a lot of rocks. Because of this, I’ve gotten pretty good at knowing what to expect and what not to expect when analyzing the chemical make-up of a Martian rock. You expect to find lots of basalt, the building block of all planets.
What I didn’t expect were large amounts of manganese. So when my colleagues and I found exactly that on a Martian rock called “Caribou” back in 2013, we thought, “This has to be a mistake.”
Trace amounts o