Like Earth and Venus, the night side of Mars emits a subtle glow, scientists reported last week in the journal Science. The night-side air glow at the red planet, elusive until now, was detected by the European Space Agency’s Mars Express orbiter. In an interview with Astrobiology Magazine, Jean-Loup Bertaux, principal investigator for the Mars Express SPICAM instrument, explains what lights up the martian evening sky, and why our understanding of that process could aid future missions to Mars.