Geoboffins spot hundreds of ghost dunes on Mars

Federico Mansilla
Julio 12, 2018

In this new study, Day and Catling identified about 300 previously undiscovered ghost dunes in the Hellas Basin-a 1600-mile long impact crater that also boasts volcanic flows and canyon systems-and almost 500 in Noctis Labyrinthus, a mazelike tangle of steep valleys. Then wind blew the sand away from the inside, leaving an empty shell behind-a "ghost dune".

The discovery was made by planetary geomorphologist Mackenzie Day and astrobiologist David Catling, both affiliated with the University of Washington in Seattle and the NASA Astrobiology Institute in California.

Existing barchian dunes on Mars. But if you really wanted to, and you lived a few billion years ago, we now know where you might have gone. About two billion years ago, streams or lava flows began covering the dunes with sediment, which hardened around them like a mold.

By comparing the ghost dunes with the modern sand dunes in the Oyama and Herschel craters, the two researchers were able to calculate their age, size, and shape.

The two researchers estimate that the ghost dunes at Noctis Labyrinthus were about 40 meters (130 feet) high when they were first buried under the lava streams, while the ones at the Hellas basin stood nearly twice as tall.

They found them by examining images of Mars' surface for clusters of crescent-shaped pits, "aligned like croissants on a baker's tray", as Lester puts it. They found that the Hellas Basin dunes averaged around 250 feet tall, while the Noctis Labyrinthus dunes were about half that.

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"One of the cool 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", said Day. This indicates that the environmental conditions on Mars have changed over time.

"The potential for eolian strata to be preserved within the pits at a once warm or water‐rich interface makes the pits of interest for astrobiology", the authors wrote in their paper.

In fact, ghost dunes occur on Earth as well and have been discovered for the first time in 2016. Discovered on the Snake River Plain in eastern Idaho, these ghost dunes date back to the late Pleistocene, reports Atlas Obscura. "If you are inside a dune, or at the bottom of a dune, and you are microbial life, the dune is protecting you from a lot of that radiation", Day said.

The paper was published after a month since NASA's announcement that Curiosity rover found evidence of the Red Planet's ability to support ancient life.

"There is probably nothing living there now", Day told Lester. "But if there ever was anything on Mars, this is a better place than average to look".

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