A team of scientists, including Dr Anna Horleston from the University of Bristol’s School of Earth Sciences, determined the quake resulted from a meteoroid impact after comparing the location of the seismically-determined epicenter with images of a yawning crater that were taken by a pair of cameras on NASA’s Mars Reconnaissance Orbiter (MRO). Offering a rare opportunity to see how a large impact shook the ground on Mars, the event and its effects are detailed in two papers published today in the journal Science.
The meteoroid is estimated to have spanned 20-to-39 feet (6-12 meters) – small enough to burn up in Earth’s atmosphere, but not in Mars’ wisp-thin atmosphere, which is just 1% as dense. The impact, in a region called Amazonis Planitia, blasted a crater roughly 492 feet (150 meters) across and 70 feet (21 meters) deep. Some of the ejecta thrown during the blast flew as far as 23 miles (37 kilometers) away.
With images and seismic data documenting the event, this is believed to be one of the largest craters ever witnessed forming anyplace in the solar system. Many larger craters exist on the planet but are significantly older and predate any Mars mission.
After studying the seismic signal of the impact, the signal of a second, slightly smaller impact was recognized in InSight’s seismic data and then verified by orbital imaging. That second impact had occurred in Sept. 2021, and is also detailed in the paper.
Dr Horleston, co-lead of the frontline team of the Marsquake Service for InSight explained: “The seismic signals from these two impacts are distinctly different to the rest of the events recorded by InSight. We immediately wondered if the source mechanisms were different but I never imagined that we’d find two craters of this size given what had been imaged before.”
InSight was sent to Mars to study the planet’s deep interior – its crust, mantle, and core – which can teach scientists about the formation of all rocky worlds, including Earth and the Moon. Seismic waves are key to the mission, and have revealed the size, depth and composition of Mars’ inner layers, including its liquid core. Since landing in November 2018, InSight’s has detected 1,318 marsquakes, including several caused by much smaller meteoroid impacts.
But the resulting quake from this impact was the first observed by the mission to have surface waves – a kind of seismic wave that ripples along the top of a planet’s crust. The second of the two papers published today in Science describes how scientists used these waves to study the structure of Mars’ crust.
Crater Hunters
In late 2021, InSight scientists reported to the rest of the team that they had detected a major marsquake on Dec. 24. Independently, the crater was first spotted on Feb. 11, 2022 by scientists working at Malin Space Science Systems, which built and operates two cameras aboard MRO. The Context Camera (CTX) provides black-and-white, medium-resolution images, while the Mars Color Imager (MARCI) produces daily maps of the entire planet, allowing scientists to track large-scale weather changes, like the regional dust storm that recently diminished InSight’s power.
The impact’s blast zone was large enough to be visible in the MARCI data that allowed the team to constrain its appearance to a 24 hour period. These orbital observations matched the seismic epicenter and conclusively demonstrated that the large Christmas Eve marsquake was in fact a meteoroid impact.
“The image of the impact was unlike any I had seen before, with the massive crater, the exposed ice, and the dramatic blast zone preserved in the Martian dust,” said Liliya Posiolova, who leads the Orbital Science and Operations group at MSSS. “I couldn’t help but imagine what it must have been like to witness the impact, the atmospheric blast and debris ejected miles downrange.”
Establishing the cratering rate is critical for refining the geologic timeline of Mars. On older surfaces, such as those of Mars and our Moon, there are more craters than on Earth, where the processes oferosion and plate tectonics erase older features from the surface.
Understanding how often large impacts occur may help mission planners protect future astronauts on Mars. Brand-new craters like these also offer insights into cratering processes and expose materials below the surface. In this case, large chunks of ice scattered by the impact were detected by MRO’s HiRISE (High-Resolution Imaging Science Experiment) color camera. Scientists think the impact dug up an icy layer below the surface.
NASA is especially interested in where subsurface ice can be found on Mars: It could be a vital resource for astronauts. Buried water ice has never been spotted this close to the Martian equator, the warmest part of Mars. That could make it easier for astronauts to dig up this ice and use it for a variety of needs, including drinking water, agriculture and rocket propellant.
Paper:
'Largest recent impact craters on Mars: Orbital imaging and surface seismic co-investigation' by LV Posiolova, A Horleston and NA Teanby in Science.