Planetary Scientists Discover New Type of Impact Craters on Mars

Northern Arizona University scientist Prof Nadine Barlow and Dr Joseph Boyce from the University of Hawaii have discovered a new class of Martian impact craters – low-aspect-ratio layered ejecta (LARLE) craters.

This image shows a 5.5 km-diameter LARLE crater on Mars. Image credit: Northern Arizona University.

This image shows a 5.5 km-diameter LARLE crater on Mars. Image credit: Northern Arizona University.

“The craters feature a thin-layered outer deposit that extends well beyond the typical range of ejecta,” said Northern Arizona University scientist Prof Nadine Barlow, who presented the results at the 45th annual meeting of the American Astronomical Society Division for Planetary Sciences.

The LARLE craters are found primarily at higher latitudes, a location that correlates with thick, fine-grained sedimentary deposits rich with subsurface ice.

“The combination helps vaporize the materials and create a base flow surge. The low aspect ratio refers to how thin the deposits are relative to the area they cover,” Prof Barlow said.

The LARLE craters display an extensive outer deposit beyond the normal layered ejecta blanket. This outer deposit extends up to 20 crater radii from the rim, terminates in a sinuous flame-like edge, and is extremely thin, leading to a low aspect ratio.

The scientists found 139 LARLE craters ranging in diameter from 1.0 to 12.2 km. 97 per cent of the LARLE craters are found poleward of 35N and 40S, with the remainder primarily found in the equatorial Medusae Fossae Formation.

The team relied on the stream of data that continues to flow from ongoing surveillance of Mars. Older data from the Mars Odyssey Orbiter was used for a global survey, but more detailed studies referred to high-resolution images from the Mars Reconnaissance Orbiter – about six meters per pixel.

“We’re looking in more detail at these deposits to find out what their characteristics are. We can see dune-like structures and the hollows that occur in the outer deposit.”

Prof Barlow said she hopes to complete the revision of her catalog of Martian craters within a year, and welcomes surprises such as the LARLE finding along the way.

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Bibliographic information: Barlow NG, Boyce JM. 2013. Characteristics and Origin of Martian Low-Aspect-Ratio Layered Ejecta (LARLE) Craters. AAS/Division for Planetary Sciences Meeting Abstracts, 45, paper #400.02