In 2018, a camera aboard the Mars Express mission saw a strangely long, shaky cloud flying over the surface of the red planet.
From a distance, the 1,500-kilometer (930-mile) foggy route almost resembled a plume of smoke and seemed to emerge from the top of a long-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 spring or summer, this curious cloud returned, before disappearing once more. The passing feather was caught in the room in 2009, 2012, 2015, 2018 and again in 2020.
A recently published study has now detailed the reasons behind this long unfathomable cloud coming and going on Mars. To do this, the researchers compared the high-resolution observations of the 2018 feather with other archived observations, some of which date back to the 1970s.
Here is the story of the cloud. Every year, at the beginning of spring or summer in the southern Martian hemisphere, the elongated cloud Arsia Mons begins to take shape.
At dawn, 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 in it condenses around dust particles, creating what here on Earth we call an orographic cloud.
Every morning, during several months of observations, the researchers watched this process repeated itself. At an altitude of about 45 kilometers, the air begins to expand, and in the next 2.5 hours or so, the cloud is pulled west by the wind, up to 600 kilometers per hour (380 mph), before it finally detaches. of volcano.
The largest, the feather can reach 1,800 kilometers in length (over 1,100 miles) and 150 kilometers in width (almost 100 miles). By noon, when the Sun is at its peak, the cloud will completely evaporate.
Ice clouds are not exactly unusual on Mars, but the clouds above Arsia Mons continue to form in the summer when most of the others disappear. In fact, most of the time, this specific volcano has a cloud above it, while others around it do not – but only under certain conditions it spreads in a long stripe. (Every year, at the beginning of winter, this cloud can form a spiral.)
Profile of the Elongated Cloud Arsia Mons. (ESA)
So, if this long feather happens daily for a period of time every year, why do we only have sporadic observations of it?
Researchers say it’s because many of the cameras orbiting Mars occasionally fly over this region in the morning, and observations are usually planned, which means we often take pictures of this cloud just by chance.
Fortunately, an old camera still on board the Mars Express mission – the Visual Monitoring Camera (VMC), which has had the power of a webcam since 2003 – has newer technology.
“Although [the camera] it has a low spatial resolution, has a wide field of view – essential to see the big picture at different local times of the day – and is great for tracking the evolution of a feature both over a long period of time and in one step. small time “, explains the astronomer Jorge Hernández Bernal from the University of the Basque Country in Bilbao, Spain.
“Therefore, we could study the entire cloud over many life cycles.”
The study is the first detailed exploration of the Arsia Mons cloud, and while 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 on our own planet. .
“Understanding this cloud gives us an interesting opportunity to try to reproduce cloud formation 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 the Country. The Basques. .
Now that we know when the cloud appears, it also allows us to direct other stronger cameras in orbit to the right place at the right time, giving us a closer look. It may not take long for the following pictures.
The study was published in Journal of Geophysical Research.