mars Unexplained plume over Mars could be caused by solar outburst

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Outlook, cloudy

 

Solar burps could be linked to unexplained clouds on Mars.

 

In March 2012, amateur astronomers around the world reported seeing a strange plume rising 250 kilometres above the surface of the Red Planet.

 

An analysis published in Nature last year concluded that clouds of frozen carbon dioxide and water particles condensing in the upper atmosphere were the most likely explanation. But the trouble is that clouds don’t form that high, either on Mars or Earth.

 

Now a team led by David Andrews at the Swedish Institute of Space Physics in Uppsala, Sweden, have used data from the orbiting Mars Express spacecraft to suggest a link between this plume and the sun. Their readings show that a coronal mass ejection (CME), a burst of high-energy plasma streaming from the sun, struck Mars around the time the plume appeared.

 

“It’s very surprising that was affecting Mars right before the plume was first observed,” Andrews says.

 

The plume was spotted over a number of days hovering above a region in Mars’s southern hemisphere, but seemed to only show up at dawn. The European Space Agency’s Mars Express was passing over the same region during those days, but at dusk, when the plume wasn’t visible.

 

But the probe might still have been able to get a reading from it, says Andrews. “If this plume exists continuously for tens of days and you expect it to rotate with the planet through the day side and back into the night, then we would hope to see something.”

 

Sun hits out at Earth

 

Intriguingly, the Nature analysis found a Hubble Space Telescope image from May 1997 that seems to show a similar plume over Mars, though this is less clear than in the 2012 images. A CME hit Earth around the same time, and while there were no spacecraft orbiting Mars back then capable of measuring the solar wind, the planet would probably also have felt its effects.

 

“There is a coincidence of both events at Mars, the CME arrival and plume observation,” says Agustin Sánchez-Lavega at the University of the Basque Country, Spain, who was first author on last year’s Nature paper. “Therefore it seems plausible there was a relation between both events.”

 

We still don’t know how a CME could have caused the plume, though. But it’s worth investigating, says Andrews, who presented the work at the European Geosciences Union in Vienna, Austria, last month.

 

“We’re not completely convinced ourselves,” he says. “At best all we can say is there is an interesting correlation between two rather extreme events.”

 

No plume in sight

 

A CME that hit Mars in 2015 was seen by NASA’s MAVEN probe, which also measured an increase in oxygen and carbon dioxide ions escaping from the upper atmosphere, but no plume was seen.

 

“It would require a massive transport of material from fairly low in the atmosphere,” says Nicholas Heavens of Hampton University in Virginia.

 

Further observations are needed to determine whether the CME connection is real, he says, but if the link holds up it could explain another Mars mystery: how the planet lost its atmosphere.

 

We know that in the past Mars had a much thicker atmosphere, making it warm and wet enough to support liquid water on the surface, but we don’t know what triggered its transition to the dry, dusty world we see today.

 

We can track changes in Mars’s atmosphere at the level of 1 per cent per decade, so any loss because of CME-driven plumes would have to be lower than that, says Heavens, but could add up over time.

 

“It would be a fairly substantial atmospheric loss mechanism,” he says. “This would change the math.”

 

“If we’re catching some kind of process in action that was occurring much more regularly in the history of Mars, then that’s a big result,” says Andrews. “At the moment, we have to be more cautious than that.”

 

One possibility is that plasma could be interacting with ice grains or dust lower down in the atmosphere and electrically charging them, boosting them higher, but it’s not clear how the effect would be big enough.

 

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