A large, strange plume first spotted on Mars about three years ago still has astronomers wondering what it could be.
According to BBC News, amateur astronomers first saw the wide-ranging haze, which popped up twice before vanishing, in 2012. Now a team of astronomers has published a study in the journal Nature on the images.
They believe the could was about 1,000km, larger than originally believed, and could have been a large cloud or an uncommonly flashy aurora. The problem is explaining how either could come to be in Mars' thin upper atmosphere.
"I noticed this projection sticking out of the side of the planet. To begin with, I thought there was a problem with the telescope or camera," Damian Peach, an amateur astronomer who was one of the first to spot the plume, told BBC News. "But as I checked more of the images, I realized it was a real feature - and it was quite a surprise."
Antonio Garcia Munoz, a planetary scientist from the European Space Agency, said the new study "raises more questions than answers." An author on the study, Munoz told BBC News the astronomers were only able to offer possible scenarios rather than concrete explanations.
"We know there are clouds on Mars, but clouds, up to this point, have been observed up to an altitude of 100km," he said. "And we are reporting a plume at 200km, so it is significantly different. At 200km, we shouldn't see any clouds, the atmosphere is too thin - so the fact we see it for 20 days in total is quite surprising.
"We know in this region on Mars, there have been auroras reported before. But the intensities we are reporting are much much higher than any auroras seen before on Mars or on Earth.
"It would be 1,000 times stronger than the strongest aurora, and it is difficult to come to terms that Mars has such an intense aurora."
