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Any way you slice it, known natural processes would struggle to produce enough antihelium for any of it to end up in our space-based detectors.

“It’s a very challenging analysis because, for every one antihelium event, there are 100 million regular helium events,” says Ilias Cholis, an astrophysicist at Oakland University, who also worked on Poulin’s study.

Samuel Ting, a Nobel laureate physicist at the Massachusetts Institute of Technology, heads the AMS team and first publicly presented the two latest possible antihelium detections—the antihelium-4 candidates—in 2018.

But the easiest of all those hard methods would be to cook up the antihelium inside antistars—which, of course, do not seem to exist.

The mystery lies in those pesky possible detections of antihelium made by the AMS, which remain unexplained.