What Martian Craters Reveal About the Red Planet's Subsurface

Traditionally, researchers have studied crater shapes and sizes to infer subsurface properties. However, new findings suggest that the dimensions of ejecta blankets - the material expelled during an impact event - can also reveal information about the underlying geology. "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."

This research was conducted by Sokolowska while she was a postdoctoral researcher at Brown University, alongside Ingrid Daubar, an associate professor (research) in Brown's Department of Earth, Environmental and Planetary Sciences.

To test this theory, Sokolowska used computer simulations, co-developed with Gareth Collins of Imperial College London, to model how different subsurface compositions affect the spread of ejected debris. The simulations considered various subsurface types, including solid bedrock, buried lake sediments, and ice-rich deposits. The results demonstrated that these different materials produce significantly different ejecta patterns.

"The differences in ejecta radius can be quite large, and we predict that they could be measured from orbit with the HiRISE camera onboard Mars Reconnaissance Orbiter," Sokolowska explained. This proof-of-concept is the focus of her current fellowship at Imperial, where she aims to refine the method into a practical tool for planetary exploration.

To validate their model, the researchers examined two recent impact craters on Mars. One crater, likely formed over solid bedrock, displayed a significantly larger ejecta blanket than another formed over icy ground, aligning with the simulation predictions.

This method has potential applications for future missions, including the European Space Agency's Hera mission, set to visit the asteroid Dimorphos in 2026. The Hera mission will study the effects of a kinetic impactor test, potentially offering similar insights into the internal structure of small bodies in space.

The research was funded by NASA, the U.K. Space Agency, and the Swiss National Science Foundation.

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