Astronomers Discover Water Frost on Mars’ Tallest Volcanoes

On early winter mornings, a thin layer of ice forms in craters atop the Red Planet’s towering peaks, near its equator, according to a new study

A simulated perspective of Olympus Mons, the tallest volcano in the solar system, with water frost at its peak.

The volcanoes along Mars’ equator are massive, imposing features, with some peaks towering more than twice the height of Mount Everest. Olympus Mons, the tallest, is as wide as France. Now, a new discovery adds to the mountains’ intrigue: the presence of early morning frost.

According to a study published Monday in the journal Nature Geoscience, a winter frost periodically covers extensive patches of Mars’ Tharsis region, home to a dozen volcanoes—providing the latest evidence of water on Mars and the first sighting of water at the planet’s equator.For a few hours each morning, before sunlight directly strikes the equator, some craters at the volcanoes’ summits are coated in a layer of water frost. This icy film is thinner than a human hair, but it covers so much area that the amount of water accumulating daily at the peaks, researchers estimate, could fill 60 Olympic-sized swimming pools.

“What we’re seeing could be a trace of a past Martian climate,” Adomas Valantinas, a planetary scientist at the University of Bern in Switzerland, tells the Guardian’s Ian Sample. “It could be related to atmospheric climate processes that were operating earlier in Martian history, maybe millions of years ago.”

Olympus Mons, seen from above, with water frost on its peak.
Olympus Mons, seen from above, with water frost on its peak. ESA / DLR / FU Berlin (A. Valantinas)

Astronomers spotted the frost when analyzing roughly 30,000 high-resolution color images of Mars captured by the European Space Agency’s (ESA) Trace Gas Orbiter. The international team confirmed the pictures were indeed of frozen water—not of carbon dioxide, which can appear similar—by calculating that the volcanoes’ temperature was too hot for carbon dioxide to freeze.

Researchers already knew the planet’s northern and southern polar ice caps hosted water ice, and the new finding adds another site to the map of Mars’ water.“This is quite exciting, because it tells you how dynamic Mars’ water system is, but also how water can be found in different amounts basically everywhere on Mars,” Valantinas tells New Scientist’s Alex Wilkins.

A map of Mars' Tharsis region, featuring some of its largest volcanoes.
A map of Mars' Tharsis region, featuring some of the planet's largest volcanoes. NASA / MGS / MOLA Science Team, FU Berlin

Scientists previously thought Mars’ equator was too hot—and its atmosphere there too thin—to support frozen ice. But the finding of frost is evidence of a more nuanced water cycle, one made possible by a microclimate atop volcanoes. There, mountain winds carry moist air into craters called calderas that are, during certain seasons, cool enough for condensation to occur.

This process is “decidedly Earth-like,” as Colin Wilson, project scientist for the Trace Gas Orbiter, says in an ESA statement.

The discovery was made with a combination of intention and luck, according to the ESA. Most other Mars orbiters are synchronized with the sun, which means they don’t observe the planet’s equator until the afternoon, when the frost has already melted away. Mars also has only a narrow, seasonal window when frost can form. The researchers were looking for frost in other equatorial regions for a different project and were surprised when they found it on volcanoes’ peaks.

Four images, captured by the ESA's Trace Gas Orbiter, show evidence of water frost on Ceraunius Tholus.
Four images, captured by the ESA's Trace Gas Orbiter, show evidence of water frost on Ceraunius Tholus, a volcano on Mars. ESA / TGO / CaSSIS

As space agencies look toward sending humans to Mars, discoveries of water are crucial, experts say.“Understanding the present day water cycle on Mars in the atmosphere and near surface will be important for future exploration missions, including human ones where water will be the key in situ resource,” John Bridges, a planetary scientist at the University of Leicester in England who was not involved in the research, tells the Guardian.

The Trace Gas Orbiter, launched in 2016, studies the chemistry of Mars’ atmosphere as it orbits the planet. It is the first part of the ESA’s ExoMars Program, which has the straightforward goal of discovering if life has ever existed on Mars. The Rosalind Franklin Rover, the program’s second act, set to launch in 2028, will land on the planet’s surface, roam around and study Martian rocks.

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