First meteoroid impact detected by NASA’s InSight mission; the image was taken by NASA’s Mars Reconnaissance Orbiter using its High-Resolution Imaging Science Experiment (HiRISE) camera. Credit: NASA/JPL-Caltech/University of Arizona
An international research team has estimated that 
This artist’s concept shows NASA’s InSight lander with its instruments deployed on the Martian surface. Credit: NASA/JPL-Caltech
Meteorite Impact Detection Methodology
Their research quest began in December 2021, a year before accumulated dust on the solar panels put an end to the InSight mission, when a large distant quake recorded by the seismometer reverberated a broadband seismic signal throughout the planet. Remote sensing associated the quake with a 150-meter-wide crater. To confirm, the InSight team partnered with Mars Reconnaissance Orbiter (MRO) Context Camera (CTX) to search for other fresh craters that would match the timing and location of the seismic events detected by InSight. The teams’ detective work paid off and they were lucky to find a second fresh crater over 100 meters (320 feet) in diameter. Smaller craters, however, formed when basketball-sized meteoroids strike the planet and which should be far more common, remained elusive. Now, the number of meteorite strikes is newly estimated by the occurrence of these special high-frequency quakes.
First Meteorite Impact Rate From Seismic Data
Approximately 17,000 meteorites fall to Earth each year, but unless they streak across the night sky, they are rarely noticed. Most meteors disintegrate as they enter Earth’s atmosphere, but on Mars the atmosphere is 100 times thinner leaving its surface exposed to larger and more frequent meteorite strikes.
Until now, planetary scientists have relied on orbital images and models inferred from well-preserved meteorite impacts on the Moon but extrapolating these estimates to Mars proved challenging. Scientists had to account for the stronger gravitational pull of Mars and its proximity to the asteroid belt, which both mean that more meteorites hit the red planet. On the other hand, regular sandstorms result in craters that are much less well-preserved than those on the Moon, and, therefore, not as easily detected with orbital imagery. When a meteorite strikes the planet, the seismic waves of the impact travel through the crust and mantle and can be picked up by seismometers.
Insights From Mars’ Seismological Data
Wójcicka explains, “We estimated crater diameters from the magnitude of all the VF-marsquakes and their distances, then used it to calculate how many craters formed around the InSight lander over the course of a year. We then extrapolated this data to estimate the number of impacts that happen annually on the whole surface of Mars.”
Zenhäusern adds, “While new craters can best be seen on flat and dusty terrain where they really stand out, this type of terrain covers less than half of the surface of Mars. The sensitive InSight seismometer, however, could hear every single impact within the landers’ range.”
Implications for Understanding Mars’ Geological Age
Much like the lines and wrinkles on our face, the size and density of craters from meteorite strikes reveal clues about the age of different regions of a planetary body. The fewer craters, the younger the region of the planet. DOI: 10.1038/s41550-024-02301-z
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