What Martian Craters Reveal About Subsurface Composition

"Historically, researchers have used the size and shape of impact craters to infer the properties of materials in the subsurface," said Aleksandra Sokolowska, a UKRI fellow at Imperial College London. "But we show that the size of the ejecta blanket around a crater is sensitive to subsurface properties as well. That gives us a new observable on the surface to help constrain materials present underground."

Sokolowska, who conducted the work while a postdoctoral researcher at Brown University, collaborated with Ingrid Daubar, an associate professor (research) in Brown's Department of Earth, Environmental and Planetary Sciences.

The study, published in the Journal of Geophysical Research: Planets, used advanced computer simulations co-developed by Gareth Collins, a professor at Imperial College London, to analyze how varying subsurface conditions affect the distance ejected debris travels. The simulations included a wide range of subsurface materials, including solid bedrock, buried lakebed sediments, loose rock mixed with ice, and solid glacial deposits.

Their results indicate that different subsurface compositions produce distinct ejecta patterns, which can potentially be measured from orbit using instruments like the HiRISE camera onboard NASA's Mars Reconnaissance Orbiter.

To validate their findings, the researchers examined two fresh impact craters on Mars. One crater, known to be located over solid bedrock, exhibited a significantly larger ejecta blanket than the second crater, which sits atop subsurface ice - aligning precisely with their model predictions.

This approach could prove valuable for future planetary missions. For instance, the European Space Agency's Hera spacecraft, set to arrive at the asteroid Dimorphos in 2026, could use similar methods to study the asteroid's internal composition by analyzing its impact ejecta.

Research Report:The Link Between Subsurface Rheology and Ejecta Mobility: The Case of Small New Impacts on Mars