Meteor Impacts on Mars Can Excavate Its Secrets – Universe Today

Examine just about any extraterrestrial body in the Solar System, and you will find that they all have the same thing in common: a long history of impacts. Whether it is the Moon, Mercury, Mars, or virtually all of the icy moons of the outer Solar System, the surface of these objects is pockmarked with craters. These craters tell a story about the evolution of these bodies and the kinds of forces that shaped them. Now, a team of researchers led by Brown University has determined that craters can be used to determine a body's subsurface composition.

The team was led by Aleksandra Sokolowska, a UKRI Fellow with the Department of Earth Science and Engineering (DESE) at Imperial College London. She was joined by Gareth S. Collins, a DESE Professor at Imperial, Ingrid J. Daubar, an Associate Professor with the Department of Earth, Environmental and Planetary Sciences (DEEPS) at Brown University, and Dr. Martin Jutzi, a Privatdozent with the Physics Institute at the University of Bern. Their research was published in the Journal of Geophysical Research: Planets. 

For decades, scientists have examined the size and shape of craters on extraterrestrial bodies to learn about what lies beneath the surface. According to Sokolowska's research, the rock layers and other ejecta produced by an impact can vary in size depending on the composition of materials beneath the impact point. Several factors play a role in altering a crater's characteristics, including the strength of the subsurface material and its porousness. This allows scientists to study planetary interiors from orbit without having to land and take drill samples.

Sokolowska performed the work with Dauba as a postdoctoral researcher at Brown University. This technique could allow scientists to spot patches of subsurface ice on Mars and other bodies based on data collected by orbiting missions. As Sokolowska indicated in a Brown University news release:

“Historically, researchers have used the size and shape of impact craters to infer the properties of materials in the subsurface. 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.”

For their study, Sokolowska and her colleagues sought to determine if crater ejecta could provide another source of information. This consisted of running models co-developed by Collins that simulate the physics of planetary impacts. The simulations also allowed them to vary the characteristics of the materials beneath the surface (single, layered, mixed) and the materials themselves (bedrock, sediment, loose rock with ice, solid glacial ice). The simulations showed that these characteristics produced a wide range of ejecta patterns.

The team then tested their results by examining two fresh impact craters on Mars, which were already known to have taken place over bedrock and subsurface ice. Since the ejected materials were young, they had not yet eroded much, making it easy to measure their distance from the impact site. They found that the ejecta pattern over the bedrock site was much larger than the one over subsurface ice. This was consistent with model predictions, confirming that differences in ejecta radius reflect subsurface properties. 

"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." Said Sokolowska. "Once the method is thoroughly tested, it could become a promising new tool for investigating subsurface properties. Turning this proof-of-concept work into a tool is the subject of my current fellowship at Imperial."

The team indicates that this method could be useful for current and future missions as they continue to explore Mars for clues about its past and where crewed missions could land someday. However, the team's findings have applications in the study of other astronomical bodies in the Solar System. This includes the double asteroid system Didymos, which the ESA's Hera spacecraft will rendezvous with in February 2026. In September 2022, NASA's Double Asteroid Redirect Test (DART) conducted the first kinetic impact test with Dimorphos, the small satellite that orbits Didymos.

When it arrives, Hera will examine the crater created by the impact to learn more about the asteroid's interior. Sokolowska said that examining the ejecta pattern could assist in this objective: "Our work suggests that ejecta that did not escape from the asteroid and blanketed its surface could hold valuable information about the asteroid's interior."

Further Reading: Brown University, JGR Planets