Cloud 950 miles long on the Martian volcano. And he has the power to stay.

A mysterious white plume extending for some 1,500 kilometers was spotted on the leeward side of the Arsia Mons volcano on Mars.

Unlike other Martian cloud structures that seem to be able to exist and disappear, this one has the power to stay, with the long flying plume near Arsia Mons since September 13 and seen until recently November 12, according to the 39, European Space Agency. The Mars Express camera from the agency records images of the mountain cloud.

"Mountain clouds are very common on Mars, but it's the length of the cloud and its duration that make it interesting," said François Forget, senior research scientist at CNRS in Paris. "Usually, it's more localized on the volcano." [The 7 Most Mars-Like Places on Earth]

Forget and his colleagues could exclude volcano spitting as the cause of the cloud: the Arsia Mons volcano has been inactive for at least 10 million years and its maximum activity is even older, there are about 150 million. years. At approximately 20 km altitude, Arsia Mons is the southernmost volcano of a group of three ancient volcanoes located on an elevated plateau called the Tharsis region on Mars.

The development of the plume, called the orographic or leeward cloud, is due to a combination of factors common in mountain regions on Mars and even on Earth.

The dust and the colder air are the main ingredients. The images of the plume were taken after the end of a dust storm on Mars. Dust storms occur, but sometimes they turn into global storms, as was the case this year.

"Dust storms create dark conditions, reduce heat on the surface of the planet and increase the absorption of solar radiation and heating by dust particles suspended in the atmosphere" said Forget. "Just like the tropical air on Earth, when this unusually warm air meets a topographic element such as a mountain or an ancient volcano such as Arsia Mons, a disturbance of the air parcel is created when she is forced up and over the volcano. "

At higher altitudes, the air temperatures are cooler and the atmosphere is finer, he added.

When the air cools to its dew point, water condenses and water ice clouds form.

"Given the conditions, ice particles do not sublime [transition directly from ice to water vapor]. As a result, the cloud carries ice water over a long distance, constantly renewed by the wind, "said Forget.The feather on Mars is similar to the varying duration of the contrails of planes."

These hot exhausted airplanes are also rich in water vapor. If the air is cold and wet, the exhaust gases condense and can freeze, like what happens with the hot and humid Martian air when it reaches these higher topographic features.

As for why the Martian plume lasts so long, Forget suggested that this is due to high humidity. The more humid the air, the more the leeward cloud is likely to renew itself on the waves of air on such a long distance on the lee side of the volcano. "We can assume that before meeting the volcano, the air was" supersaturated "with water vapor, so that when condensed, the ice in the water did not can not be sublimated, "he added.

"The fact that the same formations did not breed further north than the other volcanoes may indicate that the northern hemisphere has just started its winter solstice and is generally a cloudless period," he said. said Mr. Forget. "The southern hemisphere, where Arsia Mons is located, is just beginning its summer."

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Originally posted on Live Science.