The strange, duck-shaped comet that ESA’s Rosetta spacecraft has been orbiting for more than a year just got a bit stranger: Like plants on Earth, the comet is blowing molecular oxygen, O2, into the space around it. Molecular oxygen is thought to be rare in the cosmos – or at least exceptionally tricky to detect.

“It is the most surprising discovery we have made so far,” says Rosetta team member Kathrin Altwegg of the University of Bern. The team first spotted the oxygen about a year ago and took its time ruling out sources other than the comet itself. “The first time we saw it,” Altwegg says, “I think we all went a little bit into denial because it