Early morning frost has been spotted on some of the largest mountains in the solar system – the colossal Martian volcanoes that rise to three times the height of Mount Everest near the planet’s equator.
In colder months, the fine dust of ice, thinner than a human hair, appears to form overnight in the volcanoes’ summit craters, or calderas, and on parts of their rims, then evaporate a few hours after sunrise.
While the icy layer is exceptionally thin, it covers an enormous area. Scientists calculate that in the more frigid Martian seasons, 150,000 tons of water, equivalent to 60 Olympic swimming pools, condenses daily on the tops of the towering mountains.
“This is the first time we have discovered water frost on the volcanic mountains and the first time we have discovered water frost in the equatorial regions of Mars,” said Adomas Valantinas, a planetary scientist at the University of Bern in Switzerland and Brown University in the US.
Spacecraft in orbit around Mars have previously provided evidence for frozen and liquid water on the red planet, with significant amounts of ice seen at the north and south poles. Patterns on the landscape suggest that the planet was once a much wetter, and perhaps even habitable, world dotted with giant lakes and meandering rivers.
“What we’re seeing could be a trace of a past Martian climate,” Valantinas said of the frost-topped volcanoes. “This may be related to atmospheric climate processes operating earlier in the history of Mars, perhaps millions of years ago.”
Valantinas saw the frost-covered volcanoes in high-resolution color images taken in the early morning hours on Mars by the European Space Agency’s Trace Gas Orbiter (TGO).
With colleagues, he confirmed the discovery using a spectrometer on TGO and further images taken by the agency’s Mars Express orbiter. The frost appears as a bluish tint on the caldera floors and is absent from well-exposed slopes.
The Tharsis region of Mars is a vast volcanic plateau near the planet’s equator. It is home to a dozen large volcanoes, including Pavonis Mons and Olympus Mons, which are nearly nine and 16 miles tall, respectively, nearly twice and four times as tall as Everest. Olympus Mons is much wider than it is tall, covering an area the size of France.
Scientists thought it unlikely that frost could form on the Tharsis volcano tops because sunshine and the thin Martian atmosphere keep daytime temperatures relatively high, both on the peaks and at ground level.
But, writes in Nature Geoscience, the researchers describe how Martian winds can blow up the mountain slopes and bring more moist air into the calderas where it condenses and falls as frost at specific times of the year. Modeling of the process suggests that the frost is water ice as the peaks are not cold enough for carbon dioxide frost to form.
John Bridges, professor of planetary sciences at the University of Leicester, said the work demonstrates the continued success of the TGO mission and its Color and Stereo Surface Imaging System (CaSSIS) camera.
“Understanding the present-day water cycle on Mars in the atmosphere and near surface will be important for future exploration missions, including humans where water will be the key in situ resource,” he added.
