NASA has shown what winter is like on Mars, with snow in the shape of a cube, the landscape frozen, and frost accompanies subzero temperatures. Specifically, the coldest temperatures are reached at the poles of the Red Planet, reaching minus 123 degrees.
Despite the cold, nowhere on Mars does snow fall more than a few inches, most of it falls in very flat areas, so there are no big snowdrifts. For winter to reach Mars, it takes several months to pass due to its elliptical orbit, making a year on the planet the equivalent of about two years on Earth.
However, the planet presents unique winter phenomena that scientists have been able to study, thanks to NASA’s robotic Mars explorers. Thus, Martian snow comes in two types: water and carbon dioxide ice, or dry ice.
“If you’re looking to ski, you have to go to a crater or a cliff where snow can accumulate on an inclined surface,” said Sylvain Beccio, a scientist at NASA’s Southern California Laboratory.
Snow only occurs at the coldest temperatures on 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 the extreme cold. As a result, no photos of snowfall have ever been taken, but scientists do know that it is happening thanks to some special science tools.
Specifically, NASA’s Mars Reconnaissance Orbiter can zip through cloud cover using the Mars Climate Sounder instrument, which detects light in wavelengths imperceptible to the human eye. This ability allowed scientists to detect carbon dioxide snow falling on Earth.
In 2008, NASA sent the Phoenix probe about 1,000 miles from the north pole of Mars, where it used a laser instrument to detect frozen snow on the surface.
Because of how water molecules stick together when they freeze, snowflakes on Earth have six sides. In the case of carbon dioxide, dry ice particles always stick together in a fourth shape when they freeze. “Because carbon dioxide ice has a symmetry of four, we know that the dry snowflakes will be cube-shaped,” Becchio said, noting that these snowflakes “would be smaller than the width of a human hair.”
Both water and carbon dioxide can form frost on Mars, and both types of frost occur more widely across the planet than snow. The Vikings lander saw frozen water when they surveyed Mars in the 1970s, while NASA’s Odyssey rover observed frost formation.
At the end of winter, when the accumulated ice begins to “thaw,” it takes on bizarre, beautiful shapes that reminded scientists of “spiders, Dalmatian spots, fried eggs, and Swiss cheese.”
This “melting” also causes geysers to erupt: the transparent ice allows sunlight to heat the gas beneath, and that gas eventually erupts, sending fans of dust to the surface. In fact, scientists have begun studying these fans as a way to learn more about the way the Martian winds blow.
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