Mars methane mysteriously missing

For many years, planetary scientists have been tracking a Martian ghost: methane gas.

It was first seen by ground-based observations of Mars back in the 2000s, then subsequently by spacecraft orbiting the Red Planet. But these observations barely detected it, and have been called into question time and again. There's been much debate, and some of the claims have been contradictory. No truly convincing observation of it has been made.

So the European Space Agency sent a probe to Mars called the...