Imagine a cloud longer than the drive from Los Angeles to Las Vegas and back, appearing before sunrise and gone before lunch. On Mars, that’s a Tuesday. And a Wednesday. For about eighty days.
The Arsia Mons Elongated Cloud is a bright water-ice cloud that extends from the Arsia Mons volcano toward Olympus Mons, the tallest mountain in the solar system. At its biggest, it reaches about 1,800 kilometers, or 1,118 miles, in length and roughly 150 kilometers, or 93 miles, across. It’s what scientists call an orographic cloud, formed when wind is forced upward by terrain, and it’s the largest of its type ever seen on the planet. Earth, frankly, is a little jealous.
A daily routine
The cloud returns each year around the southern solstice on Mars, and during that season it forms and fades every day for 80 days or more, which is a work ethic Earth clouds can only dream about. New research led by Jorge Hernández Bernal, an astronomer at the University of the Basque Country, with co-author Agustín Sánchez-Lavega, looked at how it behaves from hour to hour.
They found that the cloud forms before sunrise and expands rapidly for about two and a half hours, growing at more than 600 kilometers per hour, or 373 miles per hour, before that expansion stops. It then detaches from its starting point, stretches further and evaporates by late morning. A very dramatic morning for a cloud.
Thanks, Mars Webcam
Much of the data came from the European Space Agency’s Mars Express orbiter, specifically a camera nicknamed the Mars Webcam, which was originally meant to help find the Beagle 2 lander. Mars Express supplied much of the data. The team combined its images with data from other missions, including MAVEN, Mars Reconnaissance Orbiter, Viking 2 and India’s Mars Orbiter Mission. The results were published in the Journal of Geophysical Research.
For comparison, clouds shaped by mountains on Earth are never this large or this dynamic. Mars, it turns out, does weather in a very big way, and it’s doing it on a schedule.