Mars: solved puzzle of ice clouds

Dust from meteors could provide condensation nuclei for the formation of ice clouds

How do the ice clouds of the upper Martian atmosphere originate? Perhaps tiny meteor particles serve as condensation nuclei for these clouds, as models now suggest. © NASA
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Cloud germs from space: Until now, it was unknown where the ice clouds came from in the Martian atmosphere. Now, researchers could have solved this puzzle. Thus, the condensation nuclei for these clouds are not from the surface of Mars, but from space. The dust of decaying meteors apparently provides the particles on which these ice clouds form, as the scientists report in the journal "Nature Geoscience".

Despite its thin atmosphere, Mars also has some earth-like weather phenomena, including dust storms, snow and thin, high clouds of ice crystals. But these ice clouds at a height of 30 to 60 kilometers give riddle to planetary scientists. The reason: "Clouds do not just form themselves, " says lead author Victoria Hartwick of the University of Colorado at Boulder. "They need something to condense."

Meteor dust as condensation germs?

But in the case of the ice clouds, there seemed to be no suitable condensation germs: dust from the Martian surface is not much higher than about 25 kilometers, because the atmosphere is too thin to carry the particles. And so far up in the gas envelope it also seems to be missing other suitable particles. But that's deceptive, as Hartwick and her team now demonstrate. Because Mars gets the necessary particles from outside - from space.

The starting point for this discovery was data from the NASA Mars probe MAVEN. She had already determined that there is a layer of fine meteor dust 80 to 90 kilometers above the Martian surface. These tiny particles are formed when meteors are crushed and destroyed in the atmosphere. "This meteor smoke represents an abundant and likely source of nuclei for cloud formation at high altitudes, " Hartwick and her colleagues note.

Bright night clouds in Finland. Mika Yrj l / CC-by-sa 2.0

Similar to the glowing night clouds of the earth

But is this meteorite also the originator of the Marswolken? The scientists have used a model simulation of the Martian atmosphere to verify this. The result: "Our model could not form clouds in those heights before, " says Hartwick. "But now, with the meteor dust, they are all there and in the right areas." Display

Interesting: The Martian ice clouds are preferably formed in the upper atmosphere of the polar regions, as the simulations showed. Accordingly, a large part of the meteoric dust collects at the poles, because the currents of the Martian atmosphere transport it there. The high ice clouds of Mars are strikingly similar to an earthly phenomenon: the glowing night clouds. Because even these silvery shimmering ice clouds are partly based on meteor particles as condensation germs, the researchers said.

"Heating" for the young Mars?

"We are used to seeing Earth, Mars, and other celestial bodies as self-sufficient planets that control their climate, " says Hartwick. "But the climate is not independent of the surrounding solar system." This also applies to Mars: The clouds of ice caused by the meteorites have an influence on the Martian climate. The clouds heat the atmosphere by up to ten degrees, reduce the day-night temperature difference and also influence the atmospheric circulation of Mars, as the researchers report.

However, the influence of these clouds could have been even more pronounced in the past of Mars: "More and more climate models are finding that the past climate of the planet in the time when there are still rivers on its surface It was streamed by such high clouds, "says Hartwick colleague Brian Toon. Accordingly, it is important to consider the Martian ice clouds and their conditions of education in such models. (Nature Geoscience, 2019; doi: 10.1038 / s41561-019-0379-6)

Source: University of Colorado at Boulder

- Nadja Podbregar