Ghost dunes could provide potential clues to Mars past climate
Hundreds of crescent-shaped pits on Mars may hold clues to the ancient life of the planet. These pits are a new type of dunes on Martian surface and they now go under the name of ghost dunes.
Dunes are the most common features on Mars surface and they come in different shapes and size. Newly spotted ghost dunes are actually the negative space left behind by long-vanished sand dunes and are caused by the shifting wind directions. When the wind blows and exposes the surface, it leaves a solid mold in the shape of the lost dune.
“Anyone of these pits is not enough to tell you that it’s a dune, or from an ancient dune field, but when you put them all together, they have so many commonalities with dunes on Mars and on Earth that you have to employ some kind of fantastic explanation to explain them as anything other than dunes,” said Mackenzie Day, a planetary geomorphologist at the University of Washington in Seattle and author of the new study.
“One of the coolest things about the ghost dunes is that they tell us, for sure, that the wind on Mars was different in the ancient past when they formed. The fact that the wind was different (when the ghost dunes formed) tells us that the environmental conditions on Mars aren’t static over long time scales, they have changed over the past couple billion years, something we need to know to interpret the geology on Mars.”
Ghost dunes were first discovered on Earth in eastern Idaho in 2016. Similar dunes have been detected in satellite images of Hellas basin and Noctis Labyrinthus on Mars. Satellite images show that the pit field at Noctis Labyrinthus has more than 480 potential ghost dunes, while the smooth surface in eastern Hellas Planitia is covered by more than 300 crescent-shaped pits. These pits look surprisingly similar to barchan dunes, the most common type of dune on Mars and on Earth’s deserts. The size and shape of the pits is consistent with active dune fields on Mars.
“They are all going the same way, which you would expect for dunes because they are all migrating and forming in the same wind regime,” said Day. “So just the shape and size tell us that these are features that are coming from an ancient dune system.”