On March 12, 2012, amateur skywatchers noticed something unusual coming off of Mars' southern hemisphere. It was an extremely bright plume, extending 120 miles or more into the Martian sky. Clouds, aurora, and other Martian phenomena had only ever been seen up to 80 miles high.
Now, a team of professional astronomers from Europe and the U.S. is publishing their hypotheses about what that plume could have been. In many ways, however, the plume remains mysterious. Almost nothing like it has been recorded before… and there's not one explanation astronomers are certain about.