Two cameras on the Mars Express orbiter captured images of a series of dust storms near the Martian North Pole in 2019. Analysis of the images indicates that big clouds of dust on Mars formed similarly to water vapour clouds on Earth — an unintuitive finding, given how different the planets are.
Most clouds on Earth are (obviously) not dust; they’re voluminous collections of cold water vapour. They form because of the water cycle and conditions of Earth’s atmosphere. Mars’ atmosphere is much colder than Earth’s and just 1% as dense. Yet the planet has clouds, the structure of which is explored in a paper newly published in Icarus.
The only water on Mars’ surface today is water ice. Some clouds on Mars contain water — in fact, a few were imaged by the Curiosity rover a day before the Mars Express timelapse was made. But most of the Red Planet’s clouds are made of vast amounts of dust that is churned up by winds and deposited across the planet.
“When thinking of a Mars-like atmosphere on Earth, one might easily think of a dry desert or polar region,” said Colin Wilson, project scientist on the Mars Express mission, in a European Space Agency release. “It is quite unexpected then, that through tracking the chaotic movement of dust storms, that parallels can be drawn with the processes that occur in Earth’s moist, hot, and decidedly very un-Mars-like tropical regions.”
Martian dust storms are a vexing phenomenon for space agencies; NASA’s InSight lander mission is likely to end soon because dust has clung to its solar panels, effectively choking it. A massive dust storm also ended the Opportunity rover mission in 2018.
But seen from above, the storm systems look surprisingly like Earth clouds, besides their rusty orange hue. The Martian clouds were imaged by the Visual Monitoring Camera and the High Resolution Stereo Camera on Mars Express, as well as the MARCI camera aboard NASA’s Mars Reconnaissance Orbiter.
The images show clouds formed by closed-cell convection, when columns of air rise to form small cloud cells, dimpled with abscesses where cooler air sinks below the rising air.
“Despite the unpredictable behaviour of dust storms on Mars and the strong wind gusts that accompany them, we have seen that within their complexity, organised structures such as fronts and cellular convection patterns can emerge,” said Agustín Sánchez-Levaga, a planetary scientist at the Universidad del País Vasco UPV/EHU in Spain and the lead author of the new research, in an ESA release.
Observations of clouds on Venus, today a very different world from Mars and Earth, have indicated similarly organised cloud patterns. Three upcoming missions to Venus (two by NASA, one by ESA) are slated for the early 2030s and may reveal more about the meteorology of the planet, whose evolution is often compared to Earth’s.