Mystifying giant plume above Mars leaves astronomers bewildered

Amateur astronomers across the world spotted a giant cloud-like plume more than 200 km (124 m) above the boundary of day and night (the “terminator”) of Mars. Scientists are at a loss to explain how something so massive and high could exist on the very thin atmosphere of the Red Planet.

The plume, which became visible at dawn on the edge of the Red Planet’s disc, was seen by several amateur astronomers in 2012.

Satellites orbiting the Red Planet have taken several pictures of thin cloud layers, but at heights of up to 100 km (62 m). This huge bulge was between 200 km and 250 km high and could be seen for around ten days, but only during the Martian dawn.

Giant plume Mars

The mysterious giant plume became visible in 2012, when Mars and the Earth were relatively close to each other.

Astrophysicists and cosmologists say that with their current knowledge about Mars, they are unable to explain how or why the plume appeared. They added that such a phenomenon could cause problems for future low-orbit missions to Mars.

Scientists from the University of the Basque Country in Bilbao, Spain, have written about this in the peer-reviewed journal Nature.

 

Mars has a cold, dry, thin atmosphere, where winds can blow up dust storms that can reach an altitude of 50 km (31 m).

Crystallites (tiny crystals) form in its thin ice and carbon dioxide clouds. Clouds in Mars are known to reach altitudes of up to 100 km (62 m).

Spacecraft orbiting Mars have captured images of dust clouds high above the limb or edge of the planet, but never at an altitude of 200 km.

In March/April 2012, Mars and the Earth moved relatively close to each other. During those two months, amateur astronomers across the globe captured detailed images of the planet with their high-resolution telescopes and cameras.

Excitement and bewilderment

There was immediate excitement within the scientific community when pictures of the giant plume above the “terminator” went viral, but everybody was baffled.

On its website, the University of the Basque Country wrote:

“The bulge was observed rotating with the planet above the limb for about ten days in March, which unequivocally confirmed its presence.”

“Strangely enough, after various days without being spotted, it was possible to see it once again for several days in April.”

Agustín Sánchez Lavega

Agustín Sánchez Lavega, is a Professor of Physics at the University of the Basque Country. (Image: University of the Basque Country)

The plume appeared above the Terra Cimeria, a heavily cratered, southern highland region of the planet.

Scientists analyzed some of the best images and developed a geometrical model to account for its visibility.

Prof. Agustín Sánchez Lavega and colleagues confirmed that the plume was at least 500 km (310 m) wide and reached the amazing altitude of 200 km to 250 km (124 m and 155 m) above Mars’ surface on March 20th and 21st, 2012.

This is an astronomical first; nothing like it had ever been observed before.

In May 1997, the Hubble Space Telescope managed to see similar-sized plumes above Mars’ equator, but it was not possible to measure their altitudes accurately.

Two suggested explanations for the mysterious plumes

Prof. Sánchez Lavega and colleagues say the phenomenon may either be a giant cloud or an auroral emission.

It could be an unusual cloud containing crystallites of 0.1 microns in size. However, for such water crystallites to form at an altitude of 200 km, temperatures would have to fall by over 50 degrees (100 degrees if they were carbon dioxide).

A light emission from a type of aurora may have caused the plume to become visible, the scientists suggest, given that within the Cimmeria region there is an intense magnetic anomaly that could channel charged particles coming from space and excite the emission.

Scientists say this second suggestion is not really feasible, because for that to occur it would require an emission about 1,000 times more powerful than any terrestrial aurora.

Prof. Sánchez Lavega added:

“Both hypotheses, even if they are the most plausible ones, seem impossible insofar as they challenge our current knowledge about the Martian atmosphere.”

The team in Bilbao will continue studying these high plumes to determine what the risk might be for future low-orbit or planetary entry missions.

In a Commentary in Nature, Alexandra Witze wrote that amateur astronomers watched Mars closely again in April 2014, when it was closest to Earth again, but found not high-altitude plumes. Their next such opportunity will be in 2016.

Citation: A. Sánchez Lavega, A. García Muñoz, E. García-Melendo, S. Pérez-Hoyos, J. M. Gómez-Forrellad, C. Pellier, M. Delcroix, M. A. López-Valverde, F. González-Galindo, W. Jaeschke, D. Parker, J. Phillips, and D. Peach. “An extremely high altitude plume seen at Mars morning terminator.” Nature (2015). DOI: 10.1038/nature14162.

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