It’s not often astronomers are completely stumped—especially when it comes to Mars. The planet that once held nothing but mysteries has been yielding up more and more of its secrets, thanks to the storm of probes we’ve sent its way over the decades, including the seven that are now orbiting it or trundling about on its surface. But something’s up with Mars at the moment—or at least something was up not long ago—and nobody seems able to explain it. That’s the beats-me conclusion a team of investigators reached in a new paper in Nature, when they attempted to explain a freakish plume that appeared in the Martian atmosphere in March and April of 2012, and might have occurred in 1997 as well.