According to a news release from Northern Arizona University, researchers have found a new kind of impact crater on Mars. They contend that information from underground nuclear tests and explosive volcanoes may explain how this kind of impact crater developed on the Red Planet.

The craters have a thin outer deposit that stretches many times beyond the expected range of ejecta, noted Nadine Barlow, a professor of Physics and astronomy at Northern Arizona University.

She has referred to these craters as Low-Aspect-Ratio Layered Ejecta (LARLE) craters because the ratio of the thickness to the length of the deposit is so small.

Barlow discovered the LARLE craters while examining high-resolution photos to add to her catalog of Red Planet craters. These craters caught her eye because they showed this large outer deposit beyond the typical ejecta blanket of the crater.

“I had to ask, ‘What is going on here?'” Barlow said in a statement.

Unlike the typical fluidized ejecta patterns observed around new Martian impact craters, the LARLE deposit is thin, uniform in thickness, shows dune-like features, and hollows, and ends in a twisting flame-like pattern. The long run-out distances of these outer deposits reveal that the material is positioned by a much more fluid process than the typical ejecta blankets.

Studying some “explosion literature,” Barlow and her colleagues learned more about a rare occurrence known as base surge. Augmenting gas from the collision with the Martian surface acquires fine-grained material from the surface and pushes it outward. The density of this dust cloud is much greater than that of Mars’ atmosphere, forcing the clouds to move outward as a ground-hugging current. This current can move up and over pre-existing terrain and places its payload of fine-grained material into a thin, expansive deposit.

By altering equations from volcano research for Red Planet conditions, the researchers could copy the thin, twisting, flame-like deposits associated with the LARLE layers.

The researchers found 140 LARLE craters utilizing data from the Mars Odyssey and Mars Reconnaissance Orbiter spacecraft. The craters are located mostly at higher latitudes, a place that equates with thick, fine-grained ice-rich mantles placed during periods when the Red Planet’s rotation axis was titled more than today.

“The combination of fine-grained and ice-rich materials produces the perfect condition to create a base surge,” Barlow noted.

The researchers think that most of the impacts on Mars generate a base surge, but the fine-grained deposits are rapidly taken away by the Martian winds. The LARLE deposits stay put because they are protected against erosion. Water journeying upward through the LARLE deposit shortly after its development will contain dissolved salts. These salts will create a sticky surface layer at the top of the LARLE deposit known as a duricrust, which has been spotted at several landing locations across the Red Planet.

LARLE craters are observed in the same size range and same locations on Mars as pedestal craters, which are craters which rest on a plateau raised above the surroundings. Pedestal craters are believed to develop when ice sublimates from the surrounding materials, lowering the surroundings and keeping the crater, ejecta blankets, and outer pedestal elevated.

“Based on our research, we believe that pedestal craters are simply eroded forms of LARLE craters,” concluded Barlow.