“Is there life on Mars” is a question that has vexed astrobiologists and David Bowie alike. While the latter imagined some macabre collection of arachnids on the Red Planet, NASA scientists are fixated on finding evidence that microbial life once flourished on the fourth rock from the Sun. So fixated, in fact, that the space agency has spent more than $5 billion getting two immensely complicated robotic rovers—Curiosity and Perseverance—onto the Martian surface with this specific microbial mission in mind.