In 2018, a camera aboard the Mars Express mission saw a strange long and curly cloud orbiting the surface of the red planet.
At a distance, the 1,500-kilometer (930-mile) trail looks almost like a plume of smoke, and it appears to be coming from the top of a long dead volcano.
Looking back at archival footage, researchers soon realized that this had been happening for some time. Every few years in the spring or summer, this curious cloud would return before disappearing again. The volatile plume was captured on camera in 2009, 2012, 2015, 2018 and again in 2020.
A recently published study has now outlined the reasons why this unfathomably long cloud keeps coming and going on Mars. To do so, researchers compared high-resolution observations of the plume in 2018 with other archived observations, some of which date back to the 1970s.
Here is the story of the cloud. Every year, around the beginning of spring or summer in the southern Marshal, the elongated cloud of Arsia Mons begins to take shape.
At dawn, dense air begins to climb from the base of the Arsia Mons volcano on the western slope. As the temperature drops, this wind expands and the moisture in it condenses around dust particles and creates what we here on earth call an orographic cloud.
Over the course of several months of observations, researchers saw this process repeat itself every morning. At about 45 kilometers altitude, the air begins to expand and for the next 2.5 hours the cloud is pulled westward on the wind, as fast as 600 kilometers per hour (380 mph) before it finally releases from the volcano.
At its greatest, the plume can reach 1800 kilometers long (more than 1100 miles) and 150 kilometers wide (almost 100 miles). By noon, when the sun is at its peak, the cloud will have completely evaporated.
Ice clouds are not exactly uncommon on Mars, but the clouds above Arsia Mons still form in summer when most others disappear. In fact, this particular volcano most of the time has a cloud that sits on top when others around it do not – but only in some circumstances does it spread in a long line. (Every year, at the beginning of winter, this cloud can also form a spiral.)
Profile of the Arsia Mons Elongated Cloud. (ESA)
So if this long plume occurs every year for some time, why do we have only sporadic observations of it?
Researchers say this 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 only take photos of this cloud by chance.
Fortunately, an old camera still on board the Mars Express mission – the Visual Monitoring Camera (VMC) that has the power of a 2003 webcam – does not have a single technological technology.
“Although [the camera] has a low spatial resolution, it has a wide field of view – essential to see the whole picture at different local times of the day – and it’s great to see the evolution of a function over a long period of time and in a short time to follow, “explains astronomer Jorge Hernández Bernal of the University of the Basque Country in Bilbao, Spain.
“As a result, we were able to study the entire cloud through different life cycles.”
The study represents the first detailed exploration of the Arsia Mons cloud, and although scientists say it has similar properties to orographic clouds on Earth, its size is enormous and the dynamics are quite vivid compared to what we have on our own planet. see.
“Understanding this cloud offers us the exciting opportunity to try to replicate the formation of the cloud with models – models that will improve our knowledge of climate systems on both Mars and Earth,” says astronomer Agustin Sánchez-Lavega, also from the University of Basque Country. .
Now that we know when the cloud is present, it also enables us to point other, stronger cameras at the right place to the right place at the right time, which we can see up close. It may not take too long until the following photos are.
The study is in the Journal of Geophysical Research.