Icy Clouds Kept Early Mars Warm Enough for Rivers and Lakes (Planetary Science)

Researchers from the University of Chicago have developed a model of Mars that reveals the mystery behind the red planet’s ancient climate.

The latest of NASA’s rovers to successfully land on Mars has found an advantageous location right next to an ancient river delta, and based on new computer simulations, experts believe the now-barren planet could have had a thin layer of icy clouds at one point, allowing water to flow on the surface.

The study was published Monday in the journal Proceedings of the National Academy of Sciences, where a team of researchers led by University of Chicago planetary scientist and assistant professor of geophysical sciences, Edwin Kite, discuss their explanation for Mars’ mysterious climate that has been hiding in plain sight.

After a long journey from Earth, NASA’s Perseverance became the latest rover to successfully land on Mars, joining Sojourner, Opportunity, Spirit and Curiosity. Already, the new guy has given scientists an up-close view of what used to be a flowing river on the red planet.

Contrary to what the planet looks like now, there is undeniable evidence that Mars once had many bodies of water, including oceans and rivers. The surface shows prominent signs of erosion made by flowing water and ice is in abundance, but the climate has not since been able to sustain liquid water.

This fact has had scientists scratching their heads for decades, and no one had been able to explain how a planet that received little to no warmth from the sun could sustain rivers. Lead author Kite has focused much of his research into the climate of Mars and specializes in combining climate models with geological data. Thanks to Perseverence’s invaluable findings, Kite and his team were able to propose the likely explanation of high-altitude clouds that created a greenhouse effect.

“There’s been an embarrassing disconnect between our evidence, and our ability to explain it in terms of physics and chemistry,” said Kite. “This hypothesis goes a long way toward closing that gap.”

Many scientists have proposed their own theories as to how water could have existed on Mars, including one that hypothesized that an asteroid impact could have released enough energy to warm the surface, which was later refuted. 

The researchers of this study wanted to investigate a different theory, one that had been first introduced in 2013, regarding cirrus-like clouds in the Martian atmosphere. They explained that even the smallest cloud coverage goes a long way in raising planets’ temperatures and is capable of creating a greenhouse effect.

This theory was dismissed before because scientists believed that the clouds would have to remain in the atmosphere for way longer than what was thought to be possible to have any significant effect.

“It was argued that it would only work if the clouds had implausible properties,” Kite said.

The team used a 3D model of the planet to investigate this explanation, focusing this time on a factor that was left out in previous studies: ice. They explained that if the ground was covered by ice, it would have a surface humidity that would bring low-altitude clouds, thereby not warming the planet enough to sustain water or even cooling the temperature. However, if the only ice existed in small areas, such as the planet’s poles or at high altitudes, the air could have been dry enough to welcome high altitude clouds that would have warmed the surface.

“In the model, these clouds behave in a very un-Earth-like way,” said Kite. “Building models on Earth-based intuition just won’t work, because this is not at all similar to Earth’s water cycle, which moves water quickly between the atmosphere and the surface.”

While water on Earth covers 71% of the planet’s surface and moves in quick succession through land, air and bodies of water, the water on Mars is scarce, and according to Kite, once water ends up in the atmosphere it remains there for much longer.

“Our model suggests that once water moved into the early Martian atmosphere, it would stay there for quite a long time — closer to a year — and that creates the conditions for long-lived high-altitude clouds,” said Kite.

Moving forward, NASA can test this theory on the surface of Mars using Perseverance to analyze pebbles for insight into what conditions were like when atmospheric pressure was more ideal.

“Mars is important because it’s the only planet we know of that had the ability to support life — and then lost it,” Kite said. “Earth’s long-term climate stability is remarkable. We want to understand all the ways in which a planet’s long-term climate stability can break down — and all of the ways (not just Earth’s way) that it can be maintained. This quest defines the new field of comparative planetary habitability.”

Featured image: Illustration of NASA’s Perseverance rover at work within Mars’s Jezero Crater. (Credit: NASA and JPL-Caltech)

Reference: Edwin S. Kite, Liam J. Steele, Michael A. Mischna, and Mark I. Richardson. Warm early Mars surface enabled by high-altitude water ice clouds. PNAS, 2021 DOI: 10.1073/pnas.2101959118

Provided by University of Chicago

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