A mysterious long cloud spotted on Mars way back in 2018 has been sighted on the red planet's surface once again. The white cloud over the extinct Martian Volcano has an appearance of an elongated cloud trail.

According to Science Alert, the several sightings of this mysterious long cloud is currently being studied by scientists. This phenomenon has been happening with regularity and this particular event was expected by scientists.

The white plume has its origin from the denser air close to the planet's surface. As the air is forced uphill, the temperature gets lower and moisture will condense on the dust particles. It seems that it does happen on Earth as well, and the process is called orographic lift.

Another implication is that the long-dead Arsia Mons volcano is not dead as assumed and is now alive. Besides all the speculation, if the cloud indeed came from the volcano crater, it's something the experts have to watch out for.

According to physicist Jorge Hernandez-Bernal, this phenomenon was long expected from prior observations. They have been looking into an unusual occurrence and have yet to come up with possible conclusions.

"This elongated cloud forms every Martian year during this season around the southern solstice, and repeats for 80 days or even more, following a rapid daily cycle. However, we don't know yet if the clouds are always quite this impressive," says Hernandez-Bernal.

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He is part of a group that uses the Visual Monitoring Camera (VMC) on the Mars Express probe that orbits the red planet. For the past 16 years, the spacecraft has been Earth's eyes on the Martian surface which records the seasons and days as it orbits.

Compared to a year on Earth with 365 days, on Mars, a day will be 24-hours and a year is composed of 687 days. The first time human eyes saw the cloud was in 2018, just two years back.

Scientists have spotted the cloud thanks to the Visual Monitoring Camera (VMC) on the Mars Express probe, which continues to look for exciting discoveries on the red planet.

Analysis of the visuals sent back by the Visual Monitoring Camera (VMC) has led the scientists to estimate that the cloud stretches as far as 1,800 kilometers (1,118 miles). This elongated cloud is nearly half of the North American continent.

Pictures of the enigmatic cloud was taken by the VMC on July 17 to 19. Other spacecraft in orbit will take images in the afternoon of a Martian day and Mars Express can make observations in early mornings too.

In the early morning, the cloud will make an appearance that lasts for three hours only. This happens when the southern solstice comes, with the sun located in south in the Mars sky.

According to planetary scientist Eleni Ravanis, the immense cloud needs a camera with a wider field of view. She works for the Mars Express and the European Space Agency. She added that Mars Express is equipped with a wide viewfinder that catches more land area at the start of a Martian day.

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