On March 12, 2012, amateur astronomer spotted something strange coming off of Mars' southern hemisphere. It was an enormously bright plume, covering 120 miles or more into the Martian sky. Clouds, aurora on Mars, and other Martian phenomena had only ever been observed up to 80 miles high. Now, a group of professional astronomers from Europe and the U.S. is issuing their propositions about what that plume could have been. In several ways, however, the plume remains unexplained. Nearly nothing like it has been documented before… and there's not even one explanation astronomers are positive about. After its early appearance, the plume developed over the next few days.
|Mars Plumes, images taken by W. Jaeschke and D. Parker on March 21, 2012|
On March 20 and 21, astronomers measured it to be between almost 300 and more than 600 miles extensive. It altered its shape quickly, "changing from double blob bulges to pillars or finger-plume-like morphologies," as the European-American group of astronomers wrote in their paper, distributed recently in the journal Nature. The plume persisted for at least 11 days. After that, on April 6, a second plume appeared in the same area! That plume persisted for at least 10 days. The group examined databases of images of Mars captured by both amateur astronomers and the Hubble Space Telescope, dating back to 1995. They discovered only one thing like the March-April plumes in the past: an irregular protrusion that appeared in Hubble photos taken May 17, 1997.
By means of data from telescopes on Earth, along with the 1997 Hubble data, the group calculated how deep the three plumes were, determining that the three plumes are possibly alike in composition.
Then, using simulations of Martian weather, they decided the plumes could have been huge clouds, made up of minute drops of frozen water or frozen carbon dioxide. It's also probable the plumes were auroras, 1,000 times perkier than Earth's own northern lights.
So which is the right answer? More observation would exclude some prospects, the group wrote. Even so, their notions raise more questions. For carbon dioxide or even water clouds to form at such heights, Mars' upper atmosphere must have been considerably colder than previously thought. And what about that bright aurora notion? Auroras require lots of energetic particles flowing in from the sun, but solar activity in March 2012 wasn't particularly high.