Researchers have located new craters on Mars using shock waves caused by chunks of space rock as they smash through the sky and crash into the ground.
The new scars on the face of the planet are the first impact craters ever traced from the bang and crash of meteoroids bombarding another planet. The results will help scientists get a clearer idea of how often Mars is battered by rocky detritus in the solar system and sharpen their understanding of the deep internal structure of our neighboring planet.
“This is the first time that we have felt and heard an impact on another planet,” said Professor Raphael Garcia, a planetary seismologist at the Higher Institute of Aeronautics and Space at the University of Toulouse.
To see if they could find craters produced by incoming meteoroids on Mars, the researchers examined seismic waves recorded by Nasa’s InSight lander between May 2020 and September 2021. The probe touched down in the expanse arid Elysium Planitia in November 2018 during a fact-finding mission. the planet’s structure, crust and impact activity.
Scientists expected InSight to detect between one and 100 impacts every five Earth years using a sensitive seismometer deployed on the Martian surface. The seismic data recorded by the probe included four impact events that the researchers explored in detail.
By knowing the speed at which acoustic and seismic waves pass through Martian air and rock, the team estimated how far from InSight the various meteoroids hit the surface. They then developed the direction.
The loud bang on impact sends acoustic waves racing across the surface in all directions. These deform the ground imperceptibly, but Insight’s data was so sensitive that the team picked up the direction of the impact from the slight tilt of the seismometer as the acoustic wave swept through.
The analysis allowed scientists to predict approximately where incoming meteoroids crashed onto the surface. To check for signs of new craters, they turned to images taken by NASA’s Mars Reconnaissance Orbiter. Before and after images from this probe revealed new black spots on the ground – freshly formed craters near the expected impact sites.
A meteoroid reached Mars on September 5, 2021 and triggered three brutal shock waves. The first came when it slammed into the Martian atmosphere at about 10 kilometers per second, creating a shock wave along its path. The space rock then exploded at an altitude of between 13 and 16 km, producing multiple fragments. These then slammed into the ground, creating a group of new craters several meters wide.
The data is extremely valuable to planetary scientists studying the structure of Mars’ crust, as the source of seismic waves can be traced back to the crater. But impact craters are also used as cosmic clocks, with older surfaces on planets and moons filled with more craters than younger ones.
“If people want to know if a surface is older or younger, knowing the impact rate is key, but we’re not there yet,” Garcia said. Details are published in Nature Geoscience.