In March 2012, amateur astronomers captured something big and bright coming off the surface of Mars. Estimates measured the object to be about 193 kilometers tall and as many as 966 kilometers wide. In a new paper published in Nature, scientists are speculating that the giant plume could be made of frozen CO2 or water, or maybe the phenomenon is the result of an aurora that would put Earth’s northern lights to shame. Popular Science reports that neither of those hypotheses seems to match what’s known about the martian atmosphere however, and further study will be required to solve the mystery for sure.