Mars’ tallest volcanoes found with frost

The groundbreaking discovery of water frost on Mars was made on the towering Tharsis volcanoes, which are the tallest mountains in our Solar System. Among these colossal peaks is Olympus Mons, a behemoth that rises a staggering 26 kilometers (16 miles) above the surrounding plains.

Despite the thin Martian atmosphere, the high altitudes of these volcanoes allow their surfaces to reach surprisingly warm temperatures during the day, comparable to lower elevations on the Red Planet. “At these low latitudes, the high amounts of sunshine tend to keep surface temperatures high. Therefore, we did not expect frost to be found there,” explained Dr. Adomas Valantinas, the lead author of the study.

The research team, led by Valantinas from the University of Bern, utilized high-resolution color images captured by the Colour and Stereo Surface Imaging System (CaSSIS) on board the European Space Agency’s ExoMars Trace Gas Orbiter. Analyzing over 5,000 of these images, they made the remarkable observation of thin frost deposits on the summits of the Tharsis volcanoes.

The formation of the observed water frost on the Tharsis volcanoes’ summits is driven by a fascinating interplay between Mars’ atmospheric dynamics and the unique topography of these towering peaks. According to Dr. Valantinas, the process unfolds as follows:

Upslope winds originating from the lower-lying regions carry water vapor-laden air toward the volcanoes’ summits. As this air ascends the steep slopes, it cools, causing the water vapor to condense and form thin layers of frost on the volcanic peaks.

• This phenomenon, known as orographic lifting, is a common occurrence on both Earth and Mars, where mountains act as natural barriers, forcing air masses to rise and cool.

• On Mars, the effect is amplified by the extreme elevation differences between the vast plains and the soaring volcanoes, creating ideal conditions for frost formation.

However, the existence of these frost deposits is fleeting. “As we could see from the CaSSIS images, the thin frosts are only present briefly, for a few hours around sunrise,” Valantinas noted. Once the Martian sun rises higher in the sky, its warmth quickly evaporates the frost, causing it to disappear until the next morning’s cycle.

This transient nature of the frost highlights the dynamic interplay between the Martian atmosphere and surface. The team’s findings suggest that a substantial amount of water, equivalent to approximately 150,000 tonnes or 60 Olympic swimming pools, is exchanged between the surface and atmosphere during the cold seasons on Mars.

Despite the frost’s thinness, estimated to be just one-hundredth of a millimeter, the patches cover vast areas on the volcanic summits, making them a significant contributor to Mars’ water cycle and atmospheric dynamics.