Return of the extremely elongated cloud on Mars

A mysteriously long and thin cloud has appeared again over the 20 km high Arsia Mons volcano on Mars.

A recurring feature, the cloud is made up of water ice, but despite appearances, it is not a plume linked to volcanic activity. Instead, the curious current is formed as the air flow is influenced by the ‘leeward’ slope of the volcano, the side that does not face the wind.

These images of the cloud, which can reach up to 1800 km in length, were taken on July 17 and 19 by the Visual Monitoring Camera (VMC) on Mars Express, which has been studying the Red Planet from orbit for the past 16 years. .

“We have been investigating this intriguing phenomenon and were expecting to see such a cloud at this time,” explains Jorge Hernández-Bernal, Ph.D. candidate for the University of the Basque Country (Spain) and main author of the current study.

“This elongated cloud forms every Martian year during this season around the southern solstice, and it repeats for 80 days or even more, following a fast daily cycle. However, we still don’t know if the clouds are always that impressive.”

A Martian day, or sun, is slightly longer than an Earth day at 24 hours, 39 minutes, and 35 seconds long. A year on the red planet consists of 668 soles, approximately 687 days, so the seasons last twice as long.

The southern solstice is the period of the year when the Sun is in the southernmost position of the Martian skies, just like December 21 on Earth. In the early morning hours during this period, this fleeting cloud grows for approximately three hours, and quickly disappears a few hours later.

Most spacecraft in orbit around the Red Planet tend to observe in the afternoon, however Mars Express is in a prime position to gather and provide crucial information about this unique effect.

“The range of this huge cloud cannot be seen if your camera only has a narrow field of view, or if you are only observing in the afternoon,” says Eleni Ravanis, a young graduate trainee from the Mars Express mission who works specifically for the VMC instrument.

“Fortunately for Mars Express, the spacecraft’s highly elliptical orbit, coupled with the VMC instrument’s wide field of view, allows us to take pictures covering a wide area of ​​the planet first thing in the morning. That means we can catch it. ! “

The Mars Express science team has now called the cloud Arsia Mons elongated cloud, AMEC. So how long has it been disappearing and reappearing? Why does it only form early in the morning? Stay tuned as scientists continue to investigate, and we reveal more mysteries of Mars.