‘Meteoric Smoke’ May Play Key Role in Formation of High-Altitude Clouds on Mars

Planetary scientists have long observed water-ice clouds in the Martian middle atmosphere (18.6-37.2 miles, or 30-60 km, above the surface). Now, a University of Colorado, Boulder-led study suggests that those clouds owe their existence to a phenomenon called ‘meteoric smoke.’

“Clouds don’t just form on their own. They need something that they can condense onto,” said study lead author Victoria Hartwick, a graduate student at the University of Colorado, Boulder.

On Earth, 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.

“But those sorts of cloud seeds don’t exist in Mars’ middle atmosphere. And that’s what led her and her colleagues to meteors,” Hartwick said.

“About two to three tons of space debris crash into Mars every day on average. And as those meteors rip apart in the planet’s 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’ mysterious clouds, Hartwick and her colleagues turned to computer simulations that attempt to mimic the flows and turbulence of the planet’s atmosphere.

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

“Our model couldn’t form clouds at these altitudes before. But now, they’re all there, and they seem to be in all the right places,” Hartwick said.

“Because these cluds are thin and you can’t really see them doesn’t mean they can’t have an effect on the dynamics of the climate.”

The simulations showed that middle atmosphere clouds could have a large impact on the Martian climate.

Depending on where the team looked, those clouds could cause temperatures at high altitudes to swing up or down by as much as 18 degrees Fahrenheit (10 degrees Celsius).

“Our findings on modern-day Martian clouds may also help to reveal the planet’s past evolution and how it once managed to support liquid water at its surface,” said co-author Professor Brian Toon, also from the University of Colorado, Boulder.

“More 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.”

“It is likely that this discovery will become a major part of that idea for warming Mars.”

The team’s paper is published in the journal Nature Geoscience.