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鈥檛 form that high, either on Mars or Earth.
Advertisement
Now a team led by 听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.
鈥淚t鈥檚 very surprising that was affecting Mars right before the plume was first observed,鈥� Andrews says.
The plume was spotted over a number of days hovering above a region in Mars鈥檚 southern hemisphere, but seemed to only show up at dawn. The European Space Agency鈥檚 Mars Express was passing over the same region during those days, but at dusk, when the plume wasn鈥檛 visible.
But the probe might still have been able to get a reading from it, says Andrews. 鈥淚f 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.鈥�
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.
鈥淭here is a coincidence of both events at Mars, the CME arrival and plume observation,鈥� says 听at the University of the Basque Country, Spain, who was first author on last year鈥檚 Nature paper. 鈥淭herefore it seems plausible there was a relation between both events.鈥�
We still don鈥檛 know how a CME could have caused the plume, though. But it鈥檚 worth investigating, says Andrews, who presented the work at the in Vienna, Austria, last month.
鈥淲e鈥檙e not completely convinced ourselves,鈥� he says. 鈥淎t best all we can say is there is an interesting correlation between two rather extreme events.鈥�
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鈥檚 not clear how the effect would be big enough.
No plume in sight
A CME that hit Mars in 2015 was seen by NASA鈥檚 MAVEN probe, which also measured an increase in oxygen and carbon dioxide ions escaping from the upper atmosphere, but no plume was seen.
鈥淚t would require a massive transport of material from fairly low in the atmosphere,鈥� says 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鈥檛 know what triggered its transition to the dry, dusty world we see today.
We can track changes in Mars鈥檚 atmosphere at the level of 1 per cent per decade, so any loss because of听CME-driven plumes would have to be lower than that, says Heavens, but could add up over time.
鈥淚t would be a fairly substantial atmospheric loss mechanism,鈥� he says. 鈥淭his would change the math.鈥�
鈥淚f we鈥檙e catching some kind of process in action that was occurring much more regularly in the history of Mars, then that鈥檚 a big result,鈥� says Andrews. 鈥淎t the moment, we have to be more cautious than that.鈥�
听
