Water frost discovered near the equator of Mars

“Its existence here is very interesting and hints that there are extraordinary processes occurring on Mars that allow frost to form.”

Water frost has been discovered for the first time on the equator of Mars. It was previously believed that frost could not exist in this region of the Red Planet, equivalent to its tropics.

The discovery could be crucial for modeling where water is on Mars and how it circulates between the Red Planet's atmosphere and its surface. This could be vital for future human exploration of Mars.

The water frost was spotted by two European Space Agency (ESA) spacecraft: first the ExoMars Trace Gas Orbiter (TGO), which arrived on Mars in 2016, and then Mars Express, which has been exploring the Red Planet from orbit since 2003.

Frost is located in the region of Tharsis, the largest volcanic region on Mars, where 12 large volcanoes are located. These include Mount Olympus, which is not only the tallest volcano on Mars, but also the tallest peak in the solar system – at 29.9 kilometers high, it is 2.5 times the height of Everest, the tallest mountain on Earth.

Adomas Valantinas made the discovery of “forbidden frost” on Mars while a graduate student at the University of Bern (Switzerland).

“We thought it would be impossible for frost to form near the equator of Mars because the combination of sunlight and a thin atmosphere keeps temperatures both on the surface and on mountaintops relatively warm—unlike on Earth, where you would expect to see frost-covered peaks,” it says. in a statement by Valantinas, who is now a postdoctoral researcher at Brown University. “Its existence here is very interesting and hints that there are exceptional processes that allow frost to form.”

Patches of frost appear for just a few hours around sunrise and then evaporate when sunlight hits the Red Planet's equator. In addition, frost is incredibly thin – its thickness is equivalent to the thickness of a human hair (about a hundredth of a millimeter). However, despite this, patches of frost cover a huge area of ​​each of the volcanoes, and the water content in them can fill approximately 60 Olympic swimming pools, which is about 111 million liters of water.

This water constantly circulates between the surface and atmosphere of Mars during each day, which lasts about 24 and a half hours during the cold season on the Red Planet.

The Tharsis region is home to several enormous volcanoes that rise above the surrounding plains of the Red Planet's equator. Along with Olympus, these include the volcanoes Tharsis Montes, known as Ascraeus, Arsia and Pavonis, the latter of which is approximately equal in height to Everest.

Frost has been found on the volcanoes Tharsis Olympus, Arsia Askrei and Ceraunius Tolus.

Each of these volcanoes has deep depressions at the top called “calderas” that form as chambers for magma during eruptions. The team believes that the strange way air circulates over the Tharsis region creates a microclimate in the calderas that is unique compared to the wider climate in which the volcanoes are found. It is these microclimates that allow frost spots to form.

“Winds rise up mountain slopes, carrying relatively moist air from the surface to high altitudes, where it condenses and settles as frost,” says Nicholas Thomas, principal investigator of the TGO Color and Stereo Surface Imaging System (CaSSIS) and researcher at the University of Bern. “We see this happening on Earth and other parts of Mars, and the same phenomenon causes the seasonal Martian elongated cloud Arsia Mons.”

Thomas added that the frost the team observed on the summits of volcanoes on Mars appears to settle in the shaded areas of calderas, especially in regions with cooler temperatures.

Adomas explained that there are several reasons why this frost on Mars' equator has gone undetected until now.

“First, we need an orbit that allows us to observe the site in the early morning. While ESA's two Mars orbiters – Mars Express and TGO – have such orbits and can observe at any time of the day, many of the spacecraft of other agencies are synchronized with the Sun and can only conduct observations in the afternoon,” says Adomas. “Secondly, frost deposition is associated with the colder Martian season, making the window for its detection even narrower.”

This means that in order to notice the ephemeral frost, the team either had to know exactly where and when to look for it, or they had to be very lucky.

“We were randomly looking for frost around the equator for other studies, but we didn't expect to see it on the tops of Mars' volcanoes!” Adomas added.

“The discovery of water on the surface of Mars is always exciting, both in terms of scientific interest and the implications for human and robotic exploration,” said Colin Wilson, ESA project scientist for ExoMars TGO and Mars Express. “Nevertheless, this discovery is particularly exciting.”

Wilson added that Mars' low atmospheric pressure creates an unusual situation on the Red Planet, so the planet's mountain peaks are usually no colder than its plains. Despite this, this study shows that moist air blowing onto mountain slopes can still condense into frost, which Thomas called “a completely terrestrial phenomenon.”

“This discovery was made possible thanks to the successful collaboration of both ESA Mars orbiters and additional modeling,” concluded Thomas. “Understanding exactly what phenomena are the same or different on Earth and Mars really tests and improves our understanding of the basic processes that occur not only on our home planet, but also in other parts of the cosmos.”

Study team was published Monday (June 10) in the journal Nature Geoscience.