Mars Landslides Spawned By Weird Double-Layered Craters

Double Layer Ejecta Crater on Mars
An example of a "double-layer" ejecta crater on Mars. (Image credit: NASA)

Scientists are a step closer to solving a 40-year-old mystery about some unusual looking craters on Mars.

These features are called double-layered ejecta (DLE) craters, and attracted research attention because their debris patterns do not match the typical understanding of how craters are formed.

Craters are pockmarks that form on the surface of a planet or moon when a high-speed rock smashes into the surface. The fast-moving collision sprays out dirt and other debris in a ring. There are more than 600 craters on Mars that have two layers of this debris, however. A new study suggests a glacial landslide would have created the second layer. [7 Biggest Mysteries of Mars]

The study by Brown University geology researchers David Weiss and James Head is detailed in the Aug. 7 edition of the journal Geophysical Research Letters.

Landslides on ice

The first DLEs came into view during NASA's Viking missions to Mars in the 1970s. The twin spacecraft each carried an orbiter and a lander. While the landers made the first footfalls on Mars, the orbiters remained above for years and mapped much of the planet with their cameras.

In the decades since, scientists then uncovered extensive evidence that water and ice covered much of Mars in the distant past.

The only large deposits of ice on the Red Planet today are at the north and south poles, although icy traces linger in other areas. The DLEs, however, were formed while the Martian surface was covered by a huge sheet of glacial ice, the researchers concluded after examining past climactic studies.

At maximum, this ice sheet reached to the mid-latitudes of Mars and was about 165 feet (50 meters) thick. Ice is slippery, meaning that once the crater was formed and the debris sprayed out, the dirt slid and formed a second layer on top of the first.

Groovy observations

The theory matches up with more detailed observations of DLEs, the authors said. Many of the studied craters have radial striations, or grooves radiating from the crater's epicenter. These are common in Earth landslides, particularly those that take place on glaciers.

Steep slopes are also required to make the scenario work. The scientists calculated that the craters must be smaller than 15.5 miles (25 kilometers) in diameter to form DLEs because anything larger would have too shallow a slope. They next examined hundreds of DLEs on Mars and discovered that almost every one surveyed is that size or smaller. 

DLEs also exhibit few secondary craters, which happen after thicker parts of the debris carve gouges in the surface. Because these ejecta would have landed on ice, these features would have vanished after the ice melted.

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Elizabeth Howell
Staff Writer, Spaceflight

Elizabeth Howell (she/her), Ph.D., is a staff writer in the spaceflight channel since 2022 covering diversity, education and gaming as well. She was contributing writer for for 10 years before joining full-time. Elizabeth's reporting includes multiple exclusives with the White House and Office of the Vice-President of the United States, an exclusive conversation with aspiring space tourist (and NSYNC bassist) Lance Bass, speaking several times with the International Space Station, witnessing five human spaceflight launches on two continents, flying parabolic, working inside a spacesuit, and participating in a simulated Mars mission. Her latest book, "Why Am I Taller?", is co-written with astronaut Dave Williams. Elizabeth holds a Ph.D. and M.Sc. in Space Studies from the University of North Dakota, a Bachelor of Journalism from Canada's Carleton University and a Bachelor of History from Canada's Athabasca University. Elizabeth is also a post-secondary instructor in communications and science at several institutions since 2015; her experience includes developing and teaching an astronomy course at Canada's Algonquin College (with Indigenous content as well) to more than 1,000 students since 2020. Elizabeth first got interested in space after watching the movie Apollo 13 in 1996, and still wants to be an astronaut someday. Mastodon: