On May 4, 2022, NASA’s InSight Mars lander detected a 4.7 magnitude marsquake, the biggest quake detected by the mission. Due to similarities between this quake, called S1222a, and two other large ones caused by meteorite impacts on the surface, researchers thought an impact likely caused S1222a as well.
But a new analysis of imaging of Mars’ surface from a number of missions revealed no signs of a crater or any other indications of a new impact at the time of the quake. The findings suggest that the large tremors were most likely born from geological processes below the surface instead, researchers reported October 17 in Geophysical Research Letters.
“I’m satisfied beyond reasonable doubt that this was not an impact,” Bruce Banerdt, a co-author of the study and principal investigator of the InSight mission, tells Scientific American’s Jonathan O’Callaghan.
“This represents a significant step forward in our understanding of Martian seismic activity and takes us one step closer to better unraveling the planet’s tectonic processes,” Constantinos Charalambous, a co-author of the study and planetary scientist at Imperial College London, says to Reuters’ Will Dunham.
After landing on Mars on November 26, 2018, InSight spent a little over four years studying the Red Planet’s crust, mantle and core to better understand how a rocky body becomes a planet. In total, the mission recorded more than 1,300 marsquakes, including a magnitude 4.0 quake and a magnitude 4.1 quake in 2021.
For both of these seismic events, researchers were able to spot large craters that formed at locations and times that would be expected for meteorite impacts triggering the two quakes.
Researchers thought that the 4.7-magnitude quake might also have been caused by an impact.
“This event most closely resembled two events that we already had in the catalog which we knew to be meteorite impacts, which is why we thought this might be an impact too. Impacts and tectonic events have different seismic signatures,” Benjamin Fernando, a co-author of the study and planetary geophysicist at the University of Oxford in the U.K., tells Newsweek’s Jess Thomson.
S1222a had surface waves, slow-moving waves near the planet’s surface, and the 2021 quakes were the only other events to have surface waves. The three events also had energies across a wider range of frequencies than most other events, the study authors write.
To search for a crater formed by an impact that could have triggered S1222a, the researchers organized an international collaboration. They analyzed data from twelve imaging systems operated by NASA, the European Space Agency, the United Arab Emirates Space Agency, the Indian Space Research Organization and the China National Space Administration. The work involved all eight spacecraft that were in operation around Mars in 2022, according to the paper.
The researchers searched for signs of fresh craters around where the seismic event occurred. They also looked for a blast zone, a zone where the meteorite impact or entry would have removed dust from the surface, as well as dust clouds generated by the impact.
“We would expect this crater to be so large if it did form,” Fernando tells New Scientist’s Alex Wilkins. “We’re probably talking about a crater that’s between 300 and 500 meters in diameter, and a blast zone that’s probably 100 kilometers across. It would be really hard to hide something that big.”
But the imaging didn’t reveal any signs of such disturbances, pointing instead to a tectonic source.
Earth’s crust has multiple tectonic plates that can rub up against each other and cause earthquakes. But Mars just has one tectonic plate, per Scientific American. This plate may flex and accumulate stresses from heat coming up from a cooling core. “Mars still has heat, and that heat is still trying to get out,” says Mark Panning, of NASA’s Jet Propulsion Laboratory (JPL), to Scientific American. “That’s going to cause stresses to build up that lead to marsquakes.”