The HiRISE camera aboard NASA’s Mars Reconnaissance Orbiter captured these images of frost-covered dunes just after the winter solstice. The frost here is a mixture of carbon dioxide (dry) ice and water ice, which disappears in a few months when spring arrives.Credit: NASA/JPL-Caltech/University of Arizona
Cube snow, icy landscapes, and frost are all part of Mars’ coldest season.
in winter[{” attribute=””>Mars, the surface is transformed into a truly otherworldly holiday scene. Snow, ice, and frost accompany the season’s sub-zero temperatures. Some of the coldest of these occur at the planet’s poles, where it gets as low as minus 190 degrees Fahrenheit (minus 123 degrees Celsius).
Cold as it is, don’t expect snow drifts worthy of the Rocky Mountains. No region of Mars gets more than a few feet of snow, most of which falls over extremely flat areas. And the Red Planet’s elliptical orbit means it takes many more months for winter to come around: a single Mars year is around two Earth years.
Mars also has snow, ice and frost.[{” attribute=””>NASA’s spacecraft on and orbiting the Red Planet reveal the similarities to and differences from how we experience winter on Earth. Mars scientist Sylvain Piqueux of JPL explains in this video. Credit: NASA/JPL-Caltech
Still, the planet offers unique winter phenomena that scientists have been able to study, thanks to NASA’s robotic Mars explorers. Here are a few of the things they’ve discovered:
Two Kinds of Snow
Martian snow comes in two varieties: water ice and carbon dioxide, or dry ice. Because Martian air is so thin and the temperatures so cold, water-ice snow sublimates, or becomes a gas, before it even touches the ground. Dry-ice snow actually does reach the ground.
“Enough falls that you could snowshoe across it,” said Sylvain Piqueux, a Mars scientist at NASA’s Jet Propulsion Laboratory in Southern California whose research includes a variety of winter phenomena. “If you were looking for skiing, though, you’d have to go into a crater or cliffside, where snow could build up on a sloped surface.”
HiRISE captured these “megadunes,” also called barchans. Carbon dioxide frost and ice have formed over the dunes during the winter; as this starts to sublimate during spring, the darker-colored dune sand is revealed. Credit: NASA/JPL-Caltech/University of Arizona
How We Know It Snows
Snow occurs only at the coldest extremes of Mars: at the poles, under cloud cover, and at night. Cameras on orbiting spacecraft can’t see through those clouds, and surface missions can’t survive in the extreme cold. As a result, no images of falling snow have ever been captured. But scientists know it happens, thanks to a few special science instruments.
NASA’s Mars Reconnaissance Orbiter can peer through cloud cover using its Mars Climate Sounder instrument, which detects light in wavelengths imperceptible to the human eye. That ability has allowed scientists to detect carbon dioxide snow falling to the ground. And in 2008, NASA sent the Phoenix lander within 1,000 miles (about 1,600 kilometers) of Mars’ north pole, where it used a laser instrument to detect water-ice snow falling to the surface.
NASA scientists can measure the size and shape distribution of snow particles in storms layer by layer. The Global Precipitation Mission is an international satellite project that will provide next-generation observations of rain and snow around the world every three hours. Credit: NASA’s Goddard Space Flight Center/Ryan Fitzgibbons
cubic snowflake
Snowflakes on Earth have six faces, due to the way water molecules bind together when they freeze. The same principle applies to all crystals. The way the atoms arrange themselves determines the shape of the crystal. In the case of carbon dioxide, the molecules in dry ice always combine in four forms when frozen.
“We know that dry ice snowflakes are cube-shaped because carbon dioxide ice has four symmetries,” says Piqueux. “Thanks to the Mars Climate Observatory, we can see that these snowflakes are smaller than the width of a human hair.”
The HiRISE camera captured this image of the crater rim in midwinter. The south-facing slopes of the crater, which receive less sunlight, form patches of bright frost, seen blue in this enhanced color image.Credit: NASA/JPL-Caltech/University of Arizona
Jack Frost with rover
Water and carbon dioxide can each form frost on Mars, and both types of frost appear much more widely across the globe than snow. NASA’s Odyssey Orbiter Observed frost formation and sublimation in the morning sun.
HiRISE captured this spring scene. That’s when water ice frozen in the soil splits the ground into polygons. Translucent carbon dioxide ice lets sunlight in, heats gases escaping through vents, and emits a fan of dark matter on its surface (shown in blue in this enhanced color image).Credit: NASA/JPL-Caltech/University of Arizona
strange end of winter
Perhaps the most surprising discovery is at the end of winter, when all the accumulated ice begins to “thaw” and sublimate into the atmosphere.As it does so, this ice takes on strange and beautiful shapes that give scientists Spider, dalmatian spot, fried eggWhen swiss cheese.
This “thawing” also causes geysers to erupt. Translucent ice causes sunlight to heat the gas beneath it, which eventually explodes, dust fan on the surface. Scientists actually started the study as a way to learn more about these fans. Which way does the wind on Mars blow.
