Cubed snow, icy landscapes and frost are all part of the Red Planet’s coldest season.
When winter comes to Mars, the surface transforms into a truly otherworldly holiday scene. Snow, ice and frost accompany the season’s freezing 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 snowdrifts worthy of the Rockies. No region on Mars receives more than a few meters 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 arrive: a single Martian year is about two Earth years.
Still, the planet offers unique winter phenomena that scientists have been able to study, thanks to NASA’s robotic Mars explorers. Here are some of the things they have discovered:
Two kinds of snow
Martian snow comes in two varieties: water ice and carbon dioxide, or dry ice. Because the Martian air is so thin and the temperatures so cold, water ice sublimes, or becomes a gas, before it even touches the ground. Dry snow actually reaches the ground.
“Enough fall that you could snowshoe over it,” said Sylvain Piqueux, a Mars scientist at NASA’s Jet Propulsion Laboratory in Southern California, whose research covers a variety of winter phenomena. “If you were looking for skiing, though, you’d have to go into a crater or cliff face, where snow could build up on a sloping surface.”
How we know it’s snowing
Snow occurs only at the coldest extremes of Mars: at the poles, under cloud cover and at night. Cameras on orbiting spacecraft cannot see through these clouds, and surface missions cannot survive in extreme cold. As a result, no photos of falling snow have ever been taken. But scientists know it’s happening, thanks to some special scientific instruments.
NASA’s Mars Reconnaissance Orbiter can peer through cloud cover with its Mars Climate Sounder instrument, which detects light at 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 ice snow falling to the surface.
Because of the way water molecules bond together when they freeze, snowflakes on Earth have six sides. The same principle applies to all crystals: The way atoms arrange themselves determines the shape of a crystal. In the case of carbon dioxide, molecules in dry ice always bind in the form of four when frozen.
“Because carbon dioxide ice has a symmetry of four, we know that dry ice snowflakes would be cube-shaped,” Piqueux said. “Thanks to the Mars Climate Sounder, we can say that these snowflakes would be smaller than the width of a human hair.”
Jack Frost nibbles on your rover
Water and carbon dioxide can each form frost on Mars, and both types of frost are much more common across the planet than snow is. The Viking landers saw water frost when they studied Mars in the 1970s, while NASA’s Odyssey orbiter has observed frost forming and sublimating away in the morning sun.
The wonderful end of winter
Perhaps the most amazing discovery comes at the end of winter, when all the ice that has built up begins to “thaw” and sublimate into the atmosphere. When it does, this ice takes on bizarre and beautiful shapes that have reminded scientists of spiders, Dalmatian spots, fried eggs and Swiss cheese.
This “thaw” also causes geysers to erupt: Transparent ice allows sunlight to heat the gas beneath it, and that gas eventually erupts, sending fans of dust to the surface. Scientists have actually begun studying these fans as a way to learn more about which way the Martian winds blow.
Quote: NASA explores a winter wonderland on Mars (2022, December 23) retrieved December 23, 2022 from https://phys.org/news/2022-12-nasa-explores-winter-wonderland-mars.html
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