Plumes that reached over 100 miles above the surface of Mars, reported by citizen scientist astronomers in March and April 2012, continue to puzzle scientists. In the past, similar events had been seen, but only up to around 50 miles.  

The features developed in less than 10 hours, covering an area of up to 1000 x 500 kilometers, and remained visible for around 10 days, changing their structure from day to day. None of the spacecraft orbiting Mars saw the features because of their viewing geometries and illumination conditions at the time but citizen scientists and their telescopes did. 

Government astronomers then checked archived Hubble Space Telescope images taken between 1995 and 1999 and of databases of amateur images spanning 2001 to 2014 revealed occasional clouds at the limb of Mars, albeit usually only up to 100 km in altitude. One set of Hubble images from 17 May 1997 revealed an abnormally high plume, similar to that spotted by the amateur astronomers in 2012. 




“One idea we’ve discussed is that the features are caused by a reflective cloud of water-ice, carbon dioxide-ice or dust particles, but this would require exceptional deviations from standard atmospheric circulation models to explain cloud formations at such high altitudes,” says Agustin Sanchez-Lavega of the Universidad del País Vasco in Spain, lead author of a paper on the anomaly in Nature. 



“Another idea is that they are related to an auroral emission, and indeed auroras have been previously observed at these locations, linked to a known region on the surface where there is a large anomaly in the crustal magnetic field,” adds Antonio Garcia Munoz, a research fellow at ESA’s ESTEC and co-author of the study.

The jury is still out on the nature and genesis of these curious high-altitude martian plumes. Further insights should be possible following the arrival of ESA’s ExoMars Trace Gas Orbiter at the Red Planet, scheduled for launch in 2016.