In September 2018, a mysterious white cloud formation seemed to float over the site of a volcano on Mars.
Since then, the cloud has continued to appear over Mars at the same time of the Martian year, and yet astronomers are unsure how and why it forms. However, they are now taking a closer look at this cloud formation as the European Space Agency (ESA) Mars Express mission captures images of this mysterious elongated cloud that gives astronomers a fresh look at the white cloud.
The Mars Express spacecraft captured images of the cloud on July 17 and 19 using its visual monitoring camera.
In the images, the cloud appears as a white plume that hangs over the Arsia Mons volcano on Mars, near the Martian equator, which stretches for more than 20 kilometers high. Despite claims that the cloud was an indication of volcanic activity on Mars, astronomers have concluded that this is not the case.
Instead, although the cloud is made up of water ice, it forms as an air flow due to the ‘leeward’ slope of the volcano, the side that does not face the wind, according to ESA.
The scientific team behind Mars Express has now called the cloud Arsia Mons elongated cloud, AMEC.
“We have been investigating this intriguing phenomenon and were expecting to see such a cloud at this time,” said Jorge Hernández-Bernal, Ph.D. candidate at the University of the Basque Country (Spain) and lead author of the ongoing study, said in the ESA statement.
The cloud appears during the same season each Martian year, which is equivalent to 687 days on Earth, around the southern solstice of Mars.
The southern solstice is the time of year on Mars when the Sun is in the southernmost position of the Martian skies, in the same way as December 21 on Earth.
The mysterious cloud persists for 80 days or more, with a fast daily cycle, according to the researchers. AMEC grows for about three hours in the early morning hours before quickly disappearing a few hours later.
Although clouds are common on Mars, this one was quite unusual. The Martian cloud is strangely elongated, reaching up to 1800 km in length. Another aspect that adds to its mystery is how long it lasts flying over the Red Planet, staying there for more than three months at a time, which is longer than any other cloud seen on Mars.
The Mars Express mission has been orbiting the red planet for the past 16 years, studying the interior, surface, and subsoil of Mars.
