Planets

Steamy Atmosphere Produced Clays on Mars, New Theory Suggests

Conventional wisdom holds that Mars once had a thick atmosphere capable of supporting surface water. A new proposal is entirely different.

An artist’s impression of how Mars may have appeared shortly after its formation. Visible are surface areas with clay (blues and greens) are believed to have interacted with baslatic lavas and rocks melted by impacts (browns and blacks). | Kevin Cannon
An artist’s impression of how Mars may have appeared shortly after its formation. Visible are surface areas with clay (blues and greens) are believed to have interacted with baslatic lavas and rocks melted by impacts (browns and blacks). | Kevin Cannon

The Red Planet’s watery history maybe wasn’t so wet after all. New research suggests that clay materials on Mars could have come from an early, steamy atmosphere — and not from water flowing on the surface over long periods of time.

Mars today is a dusty, dry planet with an extremely thin carbon dioxide atmosphere. But these current conditions don’t accord with observations of its ancient surface. The planet’s old river valleys and lakes are visible from orbit. And both orbiters and rovers have found some evidence on Mars of clays and minerals such as hematite, which form in water. (The evidence is somewhat scattered, as clays, for example, are only present on about 5 percent of the surface today.)

The prevailing scientific explanation holds that Mars used to have a thick atmosphere capable of supporting water at the surface. Then the atmosphere blew away and the surface dried up.

A new scenario, published in the journal Nature, proposes something entirely different.

Shortly after the Red Planet formed, outgassing from below the planet’s surface created a temporary atmosphere. This atmosphere contained water, water vapor, hydrogen, and carbon dioxide.

When this steamy atmosphere reacted with the surface rocks, the rocks were chemically altered and formed clay minerals. After a few million years (it’s not clear how long), the steam atmosphere bled away into space. Meanwhile, the clay minerals — over billions and billions of years — were buried as asteroids hit the surface and volcanism covered them over with lava. The researchers came to their conclusions using computer simulations, as well as experiments using simulated Martian rocks.

“This is a new and controversial idea.”

Shortly after the Red Planet formed, outgassing from below the planet’s surface created a temporary atmosphere. This atmosphere contained water, water vapor, hydrogen, and carbon dioxide.

When this steamy atmosphere reacted with the surface rocks, the rocks were chemically altered and formed clay minerals. After a few million years (it’s not clear how long), the steam atmosphere bled away into space. Meanwhile, the clay minerals — over billions and billions of years — were buried as asteroids hit the surface and volcanism covered them over with lava. The researchers came to their conclusions using computer simulations, as well as experiments using simulated Martian rocks.

RELATED: Earthworms Appear to Be Thriving in Simulated Martian Soil

“This is a new and controversial idea,” Kevin Cannon, a postdoctoral researcher and planetary geologist at the University Florida who led the research while studying at Brown University, told Seeker. “It’s part of this larger debate about what the climate of early Mars was like. Certainly, this is not resolved.”

The new theory, he said, “adds a new wrinkle to the puzzle, but we’ll see how it gets received.”

Mars, Cannon explained, is much smaller than the rocky planets of Venus and Earth. Conventional wisdom suggests that as the gas giants Jupiter and Saturn moved around the young solar system, the area in the vicinity of Mars was stripped of rocky and gassy material. So Mars formed early — within 10 million years of the solar system’s formation — and evolved as a stunted planet.

This meant the planet cooled down more quickly than its rocky planet neighbors, then lost its magnetic field and most of its atmosphere due to its small size. Given this planetary history, Cannon is among a group of scientists who believe Mars was always fairly cold and dry.

“What you may have had were brief punctuated periods, a few hundred to a few thousand years, where conditions got warm enough for ice and snow to melt,” he said. “The runoff could have caused these channels and lakes, but it wasn’t enough to alter the rocks.”

Mars’ formation was rapid compared to other planets in the solar system, but this meant the planet had less material to pull from and ended up with somewhat stunted growth. | Kevin Cannon

Cannon acknowledged that his theory doesn’t explain the presence of minerals such as hematite on the surface, at least not yet. An iron-oxide mineral, hematite generally forms in water-wet environments, such as from groundwater. It’s been found at the landing spots for the Opportunity and Curiosity rovers.

“That might be a different story,” Cannon said. “We didn’t really address that in the paper.”

The research genesis came from previous work by Lindy Elkins-Tanton, a planetary scientist at Arizona State University who specializes in planetary formation and evolution. (Elkins-Tanton is also principal investigator of the newly selected NASA Psyche mission. After launch in 2022, the spacecraft will explore the metallic asteroid 16 Psyche to learn more about planetary cores.)

RELATED: Gullies on Mars Probably Not Carved by Water

Elkins-Tanton’s papers showed that most rocky planets had a completely global layer of molten rock when they formed. As the rock cooled, outgassing from the surface interacted with the crust. Cannon’s team connected her theories with the clays observed on Mars, he said.

“We think that this process may have happened on other planets like Earth and Venus,” he added, noting that other researchers have suggested that Earth had an early steam atmosphere as well. The old surfaces of Earth and Venus, however, have been almost completely obliterated by geological processes such as plate tectonics, erosion, and volcanism.

Mars is an environment where old surfaces are preserved, allowing scientists to make extrapolations for planets in our own solar system — or even exoplanets. But Cannon cautioned it would be a while before telescopes can look for clay minerals on small, rocky exoplanets.

“With the James Webb Space Telescope” — which launches in 2019 — “we may be able to see outgassed atmospheres,” he said.

Other evidence could come from the Mars 2020 mission, a rover which is tasked with picking up and caching samples on the Martian surface for a potential sample-return mission. If the clays formed from a steamy atmosphere, researchers would expect to see noble gases such as krypton or xenon. But given Mars 2020’s instruments, which aren’t necessarily designed to search for these gases, Cannon suggested that samples may need to come back to Earth in order to provide definitive answers.