In 2018, a camera aboard the Mars Express mission spotted a strangely long, heavy cloud, which was gushing over the surface of the red planet.
From a distance, the 1,500-kilometer (930-mile) trail of fog almost resembled a plume of smoke and seemed to emerge from the top of a dead volcano.
Looking back at the archived images, the researchers soon realized that this had been going on for some time. Every few years in the spring or summer, this curious cloud would return before disappearing once more. Passenger lead was captured on camera in 2009, 2012, 2015, 2018 and again in 2020.
A recently published study has detailed the reasons why this unfathomably long cloud continues to come and go on Mars. To do so, the researchers compared the high-resolution observations of the 2018 plume with other archived observations, some of which date back to the 1970s.
Here is the story of the cloud. Every year, in early spring or summer in the southern hemisphere of Mars, the elongated cloud Arsia Mons begins to take shape.
In the morning, the dense air at the base of the Arsia Mons volcano begins to rise on the western slope. As temperatures drop, this wind expands and the moisture inside it condenses around dust particles, creating what we here on Earth call an orographic cloud.
Every morning, for several months of observations, the researchers observed how this process was repeated. At an altitude of about 45 kilometers, the air begins to expand, and for the next approximately 2.5 hours, the cloud blows westward through the wind, up to 600 kilometers per hour (380 mph), before finally detaching from the volcano.
At most, the feather can reach 1,800 kilometers in length (more than 1,100 miles) and 150 kilometers in width (almost 100 miles). At noon, when the Sun is at its peak, the cloud will have completely evaporated.
Ice clouds are not exactly unusual on Mars, but clouds over Arsia Mons continue to form in the summer when most others disappear. In fact, most of the time, this specific volcano has a cloud sitting on top when others around it don’t, but only under certain conditions does it extend in a long gust. (Every year, at the beginning of winter, this cloud can also form a spiral).
Profile of the elongated cloud Arsia Mons. (IS IN)
So, if this long feather occurs daily for a time each year, why do we only have sporadic observations of it?
Researchers say it is because many of the cameras orbiting Mars only occasionally fly over this region in the morning and observations are usually planned, which means we often take pictures of this cloud by chance.
Luckily, an old camera that is still aboard the Mars Express mission: the visual monitoring camera (VMC), which has the power of a 2003 webcam, has a new, more advantageous technology.
“Although [the camera] it has a low spatial resolution, has a wide field of view (essential for seeing the big picture at different local times of the day) and is wonderful for tracking the evolution of a function both over a long period of time and in a small step of time “, explains the astronomer Jorge Hernández Bernal of the University of the Basque Country in Bilbao, Spain.
“As a result, we could study the entire cloud over numerous life cycles.”
The study represents the first detailed exploration of the Arsia Mons cloud, and although scientists say it has properties similar to Earth’s orographic clouds, its size is enormous and its dynamics are quite vivid compared to what we see in the our own planet.
“Understanding this cloud gives us the exciting opportunity to try to replicate cloud formation with models: models that will improve our knowledge of climate systems on both Mars and Earth,” says astronomer Agustin Sanchez-Lavega, also of the University of the Basque Country. .
Now that we know when the cloud is occurring, it also allows us to direct other stronger cameras in orbit to the right place at the right time, which gives us a closer look. It may not be too long until the next pictures.
The study was published in Journal of Geophysical Research.