“At about 250 km, the division between the atmosphere and outer space is very thin, so the reported plumes are extremely unexpected,” says Agustin Sanchez-Lavega of the Universidad del País Vasco in Spain, lead author of the paper reporting the results in the journal Nature.
On two separate occasions in March and April 2012, amateur astronomers reported definite plume-like features developing on the planet.
The plumes were seen on two occasions in March and April 2012 rising above the same region of Mars on both occasions. A check of Hubble Space Telescope archives between 1995 and 1999 showed similar features in the past but only in one recorded case in May 1997 were they higher than 100 km off the planet’s surface.
Scientists do not know what causes the effect.
“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.
“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.
Bill Condie is a science journalist based in Adelaide, Australia.
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