You’ve already heard of blue dunes on Mars, as recently reported by the Inquisitr , but what are “ghost dunes”?
Well, as you undoubtedly know by now, the surface of the Red Planet is punctuated by sand dunes. Some of them are newer, more modern features, just like the barchan (crescent-shaped) dunes found in Oyama and Herschel craters; others are ancient and date back to billions of years, when Mars still had flowing water and active volcanoes.
In the planet’s ancient past, some of these dunes were overflown with lava, which caked their lower contours, solidifying into some sort of a cast that encased the ancient material within the sand dunes. Later, as winds swept over the top of the dunes, they carried away the upper layers of sand, leaving behind the empty casts that are now preserved as pits in the Martian surface.
Because they are hollow remnants of the ancient sand dunes, these pits or empty shells have been dubbed “ghost dunes,” and researchers have recently located about 800 of them, found clustered in two separate regions on the Red Planet, reports Science Magazine .
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.
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This is the first time that ghost dune pits have been uncovered on Mars, reveals a new study, published by Day and Catling in the Journal of Geophysical Research .
These new geological features were discovered via satellite images and are grouped in two dune fields erected in very distinct areas on Mars. About 480 of these pits were uncovered at Noctis Labyrinthus, a maze-like region of steep canyons and valleys, while 300 more ghost dunes were detected in the Hellas Planitia, a 1,600-mile long (more than 2,500 kilometers) impact crater dating back to 4 billion years ago.
Shaped Like Croissants
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.
According to GeoSpace , the blog of the American Geophysical Union, the recently discovered ghost dunes on Mars appear to be formed some 2 billion years ago in the late Hesperian, a tumultuous and transitional period in the planet’s history characterized by widespread volcanic activity and catastrophic flooding.
Chiming in on the discovery, Day noted that all common features of these sand pits point to an ancient dune system preserved by partial burial under lava flows.
“Any one 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.”
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 almost twice as tall. At a height of 75 meters (246 feet), these sand dunes were nearly the size of the U.S. Capitol building, notes Atlas Obscura .
Another peculiar thing about the ghost dunes is that they are all crescent-shaped (they look like croissants) and are oriented in the same direction, molded by winds coming from the north and gently pushing the sand south — something that’s not seen on Mars today.
“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.
A Glance Into Mars’ History
This shows that environmental conditions on Mars don’t remain static over long periods of time and have actually changed a lot in the last 2 billion years — a very important revelation for the study of Martian geology.
The reason why this is relevant is because the ghost dune pits may actually be lined with ancient dune sandstones, which could have encapsulated traces of past microbial life.
“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.
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“We know that dunes on Earth can support life,” said Day, pointing out that the sand dunes on Mars are very similar to the ones found back home.
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 .
Whether on Earth or Mars, water flow could have deposited traces of microbial life at the bottom of these ancient sand dunes. And, in the case of the Red Planet, the dunes would have provided shelter from the intense surface radiation, increasing the chances that they could still harbor some signs of past alien life, explained Day.
“There is probably nothing living there now. But if there ever was anything on Mars, this is a better place than average to look.”