A Martian cloud, measuring 1,100 mi in length and 90 mi in width (1,800×150 km) forming near the Arsia Mons volcano (which is 63,360 ft or 20 km tall), has, since its discovery, become one of the wonders of Mars.  Given its origin right next to a volcano, it’s even been speculated in some circules that it could be the result of an eruption.

But the true explanation is less spectacular, if no less interesting: it is not a column of smoke, but rather clouds of frozen water that are condensing over the peak.  This happens quite regularly atop this particular volcano.

In this case, it’s the largest “orographic” cloud ever seen on Mars, which means it’s formed with the wind is forced up by the terrain (as is the case with mountains and volcanoes) as it crosses a planet’s surface.  In this case, Arsia Mons distrubs the Martian atmosphere, triggering the cloud’s formation.  Then, humid air rises up the sides of the volcano in ascending currents, which condense at the higher altitudes, where it’s much colder.

This atmospheric phenomenon has been researched by scientists at the University of the Basque Country, using a camera nicknamed the “Mars Webcam”, which is on the European Space Agency‘s Mars Express spacecraft.  The Mars Express team decided it needed a name while they were researching its appearances and disappearances, and baptized it the “Arsia Mons Elongated Cloud”, or AMEC for short.

In 2020, a member of this team, Jorge Hernández-Bernal, explained that this stretched-out cloud formed “every Martian year at this time, around the southern solstice, and is repeated for 80 days or even more, following a rapid daily cycle.”  “However, we still don’t know if the clouds are always so impressive.”

Now, the ESA website has reported that the work of this group of scientists has been published in the Journal of Geophysical Research, which also offers a brief explanation.

Perfil de la nube alargada de Arsia Mons
Profile of the Arsia Mons Elongated CLoud

This work, led by UPV researchers, is “making the rounds across the world,” as several media outlets are reporting on it.

By the way, this is not the first time we’ve brought you reports about UPV research on the Solar System.

We’ll leave you with the ESA press release, the article published in the Journal of Geophysical Research, the series of articles published by CNET, and a list of media where you can find this news being reported.

ESA – 9/3/2021 – Europe

Mars Express unlocks the secrets of curious cloud

When spring arrives in southern Mars, a cloud of water ice emerges near the 20-kilometre-tall Arsia Mons volcano, rapidly stretching out for many hundreds of kilometres before fading away in mere hours. A detailed long-term study now reveals the secrets of this elongated cloud, using exciting new observations from the ‘Mars Webcam’ on ESA’s Mars Express.

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JGR -20/12/2020 -USA

An Extremely Elongated Cloud Over Arsia Mons Volcano on Mars: I. Life Cycle

We report a previously unnoticed annually repeating phenomenon consisting of the daily formation of an extremely elongated cloud extending as far as 1,800 km westward from Arsia Mons. It takes place in the solar longitude (Ls) range of ∼220°–320°, around the Southern solstice. We study this Arsia Mons Elongated Cloud (AMEC) using images from different orbiters, including ESA Mars Express, NASA MAVEN, Viking 2, MRO, and ISRO Mars Orbiter Mission (MOM). We study the AMEC in detail in Martian year (MY) 34 in terms of local time and Ls and find that it exhibits a very rapid daily cycle: the cloud growth starts before sunrise on the western slope of the volcano, followed by a westward expansion that lasts 2.5 h with a velocity of around 170 m/s in the mesosphere (∼45 km over the areoid).

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CNET – 9/3/2021 – USA

Scientists uncover secrets of mysterious 1,100-mile-long Mars cloud

In 2018, some corners of the internet thought there might a massive volcanic eruption on Mars, but it was a trick of the eye. A long, thin cloud appears above the Arsia Mons volcano on Mars seasonally, and now scientists have gotten a better look at how it forms and dissipates.

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CNET – 29/7/2020 – USA

Mysterious Mars cloud reappears to haunt a volcano on the red planet

The towering Arsia Mons volcano on Mars reaches over 12 miles (20 kilometers) high. It’s impressive enough on its own, but it looks extra wild when a strange cloud forms above it.  The European Space Agency Mars Express spacecraft has been keeping an eye on a “a mysteriously long, thin cloud” that periodically appears over Arsia Mons. On Wednesday, ESA released a new look at this cloud from observations made in July.

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CNET – 22/10/2018 – USA

Scientists uncover secrets of mysterious 1,100-mile-long Mars cloud

In 2018, some corners of the internet thought there might a massive volcanic eruption on Mars, but it was a trick of the eye. A long, thin cloud appears above the Arsia Mons volcano on Mars seasonally, and now scientists have gotten a better look at how it forms and dissipates.

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