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How did the Red Planet get all of its clouds? CU Boulder researchers may have discovered the secret: just add meteors.

Astronomers have long observed clouds in Mars鈥� middle atmosphere, which begins about 18 miles (30 kilometers) above the surface, but have struggled to explain how they formed.听

Now, a new study, which will be published on June 17 in the journal Nature Geoscience, examines those wispy accumulations and suggests that they owe their existence to a phenomenon called 鈥渕eteoric smoke鈥濃�攅ssentially, the icy dust created by space debris slamming into the planet鈥檚 atmosphere.

The findings are a good reminder that planets and their weather patterns aren鈥檛 isolated from the solar systems around them.听

鈥淲e鈥檙e used to thinking of Earth, Mars and other bodies as these really self-contained planets that determine their own climates,鈥� said Victoria Hartwick, a graduate student in the and lead author of the new study. 鈥淏ut climate isn鈥檛 independent of the surrounding solar system.鈥�

The research, which included co-authors Brian Toon at CU Boulder and Nicholas Heavens at Hampton University in Virginia, hangs on a basic fact about clouds: They don鈥檛 come out of nowhere.

鈥淐louds don鈥檛 just form on their own,鈥� said Hartwick, also of the at CU Boulder. 鈥淭hey need something that they can condense on to.鈥�

On Earth, for example, low-lying clouds begin life as tiny grains of sea salt or dust blown high into the air. Water molecules clump around these particles, becoming bigger and bigger until they form the large puffs that you can see from the ground. 听

But, as far as scientists can tell, those sorts of cloud seeds don鈥檛 exist in Mars鈥� middle atmosphere, Hartwick said. And that鈥檚 what led her and her colleagues to meteors.听

Meteoric smoke

Hartwick explained that about two to three tons of space debris crash into Mars every day on average. And as those meteors rip apart in the planet鈥檚 atmosphere, they inject a huge volume of dust into the air.

To find out if such smoke would be enough to give rise to Mars鈥� mysterious clouds, Hartwick鈥檚 team turned to massive computer simulations that attempt to mimic the flows and turbulence of the planet鈥檚 atmosphere.

And sure enough, when they included meteors in their calculations, clouds appeared.听

鈥淥ur model couldn鈥檛 form clouds at these altitudes before,鈥� Hartwick said. 鈥淏ut now, they鈥檙e all there, and they seem to be in all the right places.鈥�

The idea might not be as outlandish as it sounds, she added. Research has shown that similar interplanetary dust may help to seed clouds near Earth鈥檚 poles.

But she also says that you shouldn鈥檛 expect to see gigantic thunderheads forming above the surface of Mars anytime soon. The clouds her team studied were much more like bits of cotton candy than the clouds Earthlings are used to.听

鈥淏ut just because they鈥檙e thin and you can鈥檛 really see them doesn鈥檛 mean they can鈥檛 have an effect on the dynamics of the climate,鈥� Hartwick said.

The researchers鈥� simulations, for example, showed that middle atmosphere clouds could have a large impact on the Martian climate. Depending on where the team looked, they caused temperatures at those high altitudes to swing up or down by as much as 18 degrees Fahrenheit (10 degrees Celsius).

And that climactic impact is what gets Brian Toon, a professor in ATOC, excited. He said that the team鈥檚 findings on modern-day Martian clouds may also help to reveal the planet鈥檚 past evolution and how it once managed to support liquid water at its surface.听

鈥淢ore and more climate models are finding that the ancient climate of Mars, when rivers were flowing across its surface and life might have originated, was warmed by high altitude clouds,鈥� Toon said. 鈥淚t is likely that this discovery will become a major part of that idea for warming Mars.鈥�
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