The largest volcanoes on Mars have frosted tips during winter

As winter mornings dawn on Mars, the tips of its largest volcanoes become covered in frost, in yet another example of water on the Red Planet.

We already know that Mars has significant deposits of ice in the form of polar ice caps, and possibly buried underneath the surface at the equator, but scientists had yet to observe surface water in other Martian regions.

Now, Adomas Valantinas at Brown University in Rhode Island and his colleagues have spotted frost that appears to only form in the morning, during Martian winters, near the peaks of volcanoes in the Tharsis region, which includes some of the solar system’s largest volcanoes, such as Olympus Mons. “This is quite exciting because it tells you how dynamic Mars’s water system is, but also how water can be found in different amounts basically everywhere on Mars,” says Valantinas.

He and his team took morning pictures of the icy volcanic peaks using a colour camera aboard the European Space Agency’s Trace Gas Orbiter, which studies the Martian atmosphere, and spotted wide regions of blue frost. They ruled out frozen carbon dioxide, which can look similar, as the cause by calculating the surface temperatures and finding it was too warm for CO2 to freeze.

Though there is a possibility the ice is formed from gases coming out of the volcano, Valantinas and his team would it expect to see it all year round if this was the case. Instead, the fact that it only appears during the colder parts of the year, makes it more likely the frost is a result of water vapour in the atmosphere freezing out.

Knowing where ice forms on the Martian surface, especially from atmospheric processes, is vital for accurate weather prediction, says Susan Conway at the University of Nantes, France. We know that ice from the poles moves into the atmosphere, but we don’t know where it goes, she says. “This is a really neat observation, because we can actually see where it’s going.”