Strange plumes that have been observed above the surface of the Red Planet are baffling scientists.
This image shows the location of the mysterious plume (circled) on Mars; south is up. Image credit: W. Jaeschke / D. Parker.
On two separate occasions in March and April 2012, amateur astronomers reported bright, extremely high-altitude plumes developing on Mars.
The plumes were seen rising to altitudes of 200 – 250 km above the same region, Terra Cimmeria, on both occasions.
The features developed in less than ten hours, covering an area of up to 1,000 by 500 km.
They were seen at the morning terminator, exhibited day-to-day variability, and remained visible for around ten days.
None of the spacecraft orbiting the planet saw the features because of their viewing geometries and illumination conditions at the time.
An international team of scientists from Spain, France, the Netherlands, the United States and the UK, led by Prof Agustin Sanchez-Lavega from the Universidad del País Vasco in Spain, is now working on determining the nature and cause of the plumes by using the data from the Hubble Space Telescope in combination with the images taken by ground-based telescopes.
“At about 250 km, the division between the atmosphere and outer space is very thin, so the reported plumes are extremely unexpected,” explained Prof Sanchez-Lavega, who is the first author of the paper published in the Nature.
However, checking archived Hubble images taken between 1995 and 1999 and of databases of amateur images spanning 2001 to 2014 revealed similar plumes, albeit usually only up to 100 km in altitude.
Different views of the changing plume morphology taken by amateur astronomers on March 21, 2012. Image credit: W. Jaeschke / D. Parker.
One set of Hubble images from May 17, 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,” Prof Sanchez-Lavega said.
“For water crystallites to be able to form at an altitude of 200 km, the temperature would need to fall more than 50 degrees (100 degrees if they were of carbon dioxide) with respect to what is predicted by the current models of Mars.”
Dr Antonio Garcia Munoz, a researcher at the European Space Agency and a co-author on the study, added: “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.”
“Importantly, both explanations defy our current understanding of Mars’ upper atmosphere,” the scientists said.
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A. Sánchez-Lavega et al. An extremely high-altitude plume seen at Mars’ morning terminator. Nature, published online February 16, 2015; doi: 10.1038/nature14162
