Did you know that there are volcanoes on Mars? Arsia Mons, one of the Martian volcanoes, has been getting a lot of attention from scientists. Is it about to erupt? The volcano has been dormant for millions of years, but something very strange has formed on top of it.

950 mile long cloud

On one side of Arsia Mons, a cloud formed that was so long, 950 miles long to be exact, that it could be seen by satellites. As if being incredibly long wasn’t noteworthy enough, the cloud also gained the attention of scientist because it wouldn’t move. Clouds on Mars can get much larger than clouds on Earth, but 950 miles is large even for Martian standards, and they usually disappear after a short amount of time.

From far away, this huge cloud looked like a streak, or even a comet, flying across the surface of Mars. What could have caused such a humongous cloud?

Dustorm of a lifetime

Mars, which is about half the size of Earth, has some extremely different weather patterns. Since the planet is so much smaller than Earth, not to mention it has less water and a completely different gravitational pull, weather patterns can impact all of Mars at one time. Scientists have linked this record-breaking cloud to a dust storm that covered all of Mars.

Mars is very, very dusty, so sustained winds cause dust storms worthy of nightmares. If these types of storms happened on Earth, they would likely cause every living thing in its path to suffocate. In a particularly ferocious planetwide dust storm, a big mass of dust and partially melted ice got trapped inside each other. As the ice attempted to melt and responded to other weather forces, this snowball of sorts got suspended in the air as a cloud.

Why wouldn’t the cloud move?

If you’ve ever looked at the sky for a long time, you’ll notice that clouds on Earth move around. Sometimes they move fast and sometimes slow. Wind moves the clouds in any direction, which is why thunderstorms and hurricanes don’t keep pounding on the same spot forever. Since wind is what created this huge, Martian dust ball of a cloud, why didn’t the wind make it move as well?

This cloud was made of a constantly changing blend of water and ice. The dust on Mars can get so thick at times that it blocks out the sunlight, and that’s what happened in this case.

Credit: ESA/GCP/UPV/EHU Bilbao

The temperatures on Mars are usually far below freezing with sunlight, so a lack of sunlight only makes it even colder. The cloud started out as dust and ice. Alternating cycles of cold and humid air caused the moisture in the cloud to freeze and then to melt. This cycle repeated itself several times, which is what caused the cloud to stay put.

NEXT: The intrepid InSight Lander recently touched down on Mars and got right to work studying the Red Planet in hopes that one day, we might travel there ourselves.