Morning frost – on Mars? How a 'surprise' discovery offers new insights

An early morning frost has been discovered for the first time atop the tallest volcanoes in the solar system, found near Mars' equator, changing what planetary scientists thought they knew about Mars' climate.

The discovery shows that "Mars is a dynamic planet," and that water in solid form can be found at all latitudes on Mars, according to lead researcher Adomas Valantinas, who is a postdoctoral fellow at the Brown University Department of Earth, Environmental and Planetary Sciences. Valantinas led the work while he was a Ph.D. student at the University of Bern in Switzerland.

In new research published in the Nature Geoscience journal this week, the researchers said the frost suggests there are microclimates on Mars, with a unique climate within the volcanoes' caldera, the depression at the top of the volcanic mountains. The frost gives scientists insight into the water cycle on the Red Planet.

"Mars always gives us surprises," Valantinas told USA TODAY. "That's the beauty of science."

How was the frost discovered?

Researchers first detected the frost in images taken by the Color and Stereo Surface Imaging System (CaSSIS) onboard the European Space Agency’s Trace Gas Orbiter. Valantinas said those images were validated using another camera on board the ESA's Mars Express orbiter and a spectrometer also on the Trace Gas Orbiter.

The team analyzed thousands of images and ran computer simulations to confirm the frost's existence.

What the unexpected discovery says about Mars' climate

Researchers weren't expecting to see frost at the planet's equator, Valantinas said, because of how dry the atmosphere and warm the surface temperatures are there compared to the rest of the planet. The frost might be a sign that ancient climates in the region had more precipitation and snowfall, leading to ice deposits on the volcanoes.

The frost deposits were observed on the rims of the volcanoes only during early morning hours and return as vapor into the atmosphere as the temperature warms, Valantinas said. Craters that always saw sunshine didn't develop the frost. The way the air circulates above the volcanoes allows the frost to form.

"You can see the same phenomenon ... on Earth where during winter time, you wake up in the morning and you go out in your garden and you see the thin, whitish frost deposits on ground and they disappear if there is sunshine later in the afternoon," he said.

Volcanoes in the Tharsis region, where the frost was found, include Olympus Mons, the largest known volcano in the solar system at 16 miles tall. Its caldera is 50 miles wide, according to NASA, and it could fit all the Hawaiian islands inside.

The frost found there is thin – roughly the width of a human hair, the researchers found, but widespread. Within the calderas of the volcanoes, the water that swaps between the surface and atmosphere each day during cold Martian seasons could fill 60 Olympic-size swimming pools, about 150,000 tons of water.

Why did it take so long to discover the frost? The window for spotting it was narrow, because it only occurs in early mornings during colder Martian seasons, Valantinas said in a press release from the European Space Agency.

"In short, we have to know where and when to look for ephemeral frost. We happened to be looking for it near the equator for some other research, but didn't expect to see it on Mars’s volcano tops!” Valantinas said.