When you picture winter on Earth, you probably conjure up images of beautiful snow-covered trees and icicles dangling from houses. But on Mars, winter decorates the martian surface in truly otherworldly ways, as recently documented by NASA’s Mars Reconnaissance Orbiter (MRO).
During winter on Mars, the planet's poles can experience nighttime temperatures as low as –190 degrees Fahrenheit (–123 degrees Celsius), which creates ideal conditions for both snowfall and the formation of frost. But unlike Earth snow, Mars snow comes in two forms: water ice and frozen carbon dioxide, or dry ice.
Captured by MRO's HiRISE camera, the image above shows rippling sand dunes coated by a layer of frost made of both water ice and carbon dioxide ice, giving the dunes an alluring blue sheen. MRO captured this shot just two days after winter solstice for Mars' northern hemisphere, which occurred July 21, 2022.
When spring arrives on Mars, frosted dunes like these thaw out, revealing much darker sand hiding beneath, as seen in the image below.