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.
The newest plume, which rose an unprecedented 155 miles (250 km) high in the Martian sky, was first observed by Wayne Jaeschke, an amateur astronomer in West Chester, Pa. on March 12, 2012. He sent the word out across the amateur astronomer community and soon reports were coming back that yes, other backyard sky-watchers were seeing the same thing. The plume lasted for 11 days and then recurred on April 6, this time hanging around for 10 days. Both phenomena appeared in the same spot in Mars’s southern hemisphere.
Plumes aren’t unheard of on Mars. The planet does have an atmosphere, after all—albeit one only 1% the thickness of Earth’s—and both dust and ice crystals can swirl up into the sky. Aurorae may also appear when charged particles streaming in from the sun interact with the planet’s magnetic field, which can create a plume-like effect.
But ice crystals have never been observed to climb above an altitude of 62 miles (100 km). Aurorae occur higher in the Martian sky, but at a maximum of 80 miles (130 km), they fall short too. And dust storms don’t even come close.
But those three are the only known explanations for what Jaeschke and the others saw—or at least the only known ones—and the mere fact that dust or ice or aurorae have never behaved this way before does not mean that they can’t. So a team of researchers led by Agustín Sánchez-Lavega of the University of the Basque Country in Bilbao, Spain, decided to put all three theories to the test.
The investigators began their work by studying not just the images of the plumes but also roughly 3,500 pictures of Mars captured by amateur astronomers around the world from 2001 to 2014, as well as a series of shots taken by the Hubble space telescope from 1995 to 1999, when it was giving the Red Planet a good going-over. None of these pictures showed anything anything similar to the 2012 phenomena except for a single shot taken by Hubble on May 17, 1997, which did show a similar plume in a similar spot.
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SOURCE: TIME, Jeffrey Kluger