Mars isn’t just red. Some parts are much darker. NASA highlights one of these areas in an image captured by the Mars Reconnaissance Orbiter (MRO). Have a look at dark sands covering a small portion of the planet’s rocky surface.
The Ganges Chasma, a canyon in the Valles Marineris system. This canyon system measures 2,500 miles long and can reach depths of up to 4 miles. The Grand Canyon on Earth is just 500 miles long and 1 mile deep.
These Martian sand dunes can thank iron and magnesium-rich sand for the darker appearance.
NASA took a much closer look at Mars’ dark sand back in late 2015/early 2016. The Curiosity rover took a big scoop of dark sand at the ‘Namib Dune.’ Check out the rover wheel-deep in a Martian selfie.
Here’s another image captured by Curiosity showing dark dunes at the Bagnold Dune Field. This image has been brightened to highlight the ripples in the black sand.’
Some of the ripples seen above tease clues about Mars atmosphere’s history. There are mid-sized ripples that aren’t seen on sand dunes on Earth.
“The size of these ripples is related to the density of the fluid moving the grains, and that fluid is the Martian atmosphere,” he said. “We think Mars had a thicker atmosphere in the past that might have formed smaller wind-drag ripples or even have prevented their formation altogether. Thus, the size of preserved wind-drag ripples, were found in Martian sandstones, may have recorded the thinning of the atmosphere.”
A quick look at ripple textures in 3 billion-year-old sandstone shows wind-drag ripples of around the same size as those seen on active dunes today. That lines up with other evidence that Mars lost a good chunk of its original atmosphere early in its history.