Clouds on Mars could have been caused by meteors

How did Mars get its clouds? New research suggests the key ingredient could have been meteors.

Clouds in Mars’ middle atmosphere, which begins about 18 miles — 30 kilometres — above the surface, have been known to scientists and astronomers but they have, thus far, struggled to explain how they formed. A new study — published on June 17th in the journal Nature Geoscience — may have solved this martian cloud mystery.

The paper from researchers at CU Boulder examines those wispy accumulations suggesting that they are a result of a phenomenon known as meteoric smoke — the icy dust created by space debris slamming into the planet’s atmosphere.

An important aspect of the paper’s findings is the reminder that the atmospheres of planets and their weather patterns should not be considered isolated from their host solar systems.

Victoria Hartwick is a graduate student in the Department of Atmospheric and Ocean Sciences (ATOC) and lead author of the new study. She elaborates: “We’re used to thinking of Earth, Mars and other bodies as these really self-contained planets that determine their own climates. But climate isn’t independent of the surrounding solar system.”

Discovering the origins of martian cloud seeds

The research — co-authored by Brian Toon at CU Boulder and Nicholas Heavens at Hampton University in Virginia — centres on the fact clouds seem to form from nowhere.

Hartwick points out that this doesn’t mean they appear spontaneously. She says: “Clouds don’t just form on their own. They need something that they can condense onto.”

An example is clouds on our own planet — low-lying clouds begin life as tiny grains of sea salt or dust blown high into the air, water molecules then collate around these particles. This gathering of water molecules becomes bigger and bigger eventually forming the accumulations we can see from the ground.

Hartwick says that the problem in cracking the martian cloud mystery is that those sorts of cloud seed don’t exist in Mars’ middle atmosphere. Thus leading and her colleagues to suspect meteors and space debris could act as defacto cloud seeds.

As Hartwick says — approximately two to three tons of space debris crash into Mars every day, ripping apart the planet’s atmosphere and injecting a huge volume of dust into the air.

To discover if those dust clouds would be sufficient to give rise to Mars’ mysterious clouds, Hartwick and her team created massive computer simulations to model the flows and turbulence of the planet’s atmosphere. When they accounted for meteors in their calculations — clouds appeared.

Hartwick says: “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 and her team Mars cloud simulations (Hartwick)

Whilst Hartwick concedes that the model may initially sound unlikely, research has also shown that similar interplanetary debris and dust may help to seed clouds near Earth’s poles.

Despite this, the team warn that we shouldn’t expect to see gigantic thunderheads forming above the surface of Mars anytime soon as the clouds produced in the simulation were more thin and nebulous than those we experience on Earth.

A NASA balloon mission examined the rippling, electric blue clouds found high over Earth’s poles during twilight in summertime. (NASA)

Hartwick adds that just because are thin and wouldn’t be visible to the naked eye, that doesn’t mean they can’t have an effect on the dynamics of the climate. The simulations show that middle atmosphere clouds, for instance, 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 10⁰ C.

It is this climactic impact which Brian Toon — a professor in ATOC — finds most compelling. He believes that the team’s findings with regards to modern-day Martian clouds may also help to reveal details of the red planet’s evolution including how it once managed to support liquid water at its surface.

Toon points out: “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.”

Original research: http://dx.doi.org/10.1038/s41561-019-0379-6