An international team of researchers, co-led by ETH Zurich and Imperial College London, has made a groundbreaking discovery regarding the frequency of meteorite impacts on Mars. Using seismic data from the NASA InSight Mission, the team determined that the Red Planet experiences between 280 to 360 meteorite strikes each year, forming impact craters over 8 meters (26 feet) in diameter.

Previously, estimates of meteorite impacts on Mars were based on orbital imagery alone, which suggested a much lower rate. However, the seismic data collected by the InSight mission provided a more accurate measurement. The researchers found that the seismometer recorded specific acoustic signals generated when meteorites enter the Martian atmosphere, allowing them to identify six seismic events as meteoric impacts. Further analysis revealed that these events belonged to a larger group of marsquakes known as very high frequency (VF) events. The impact-generated quakes were distinct from tectonic marsquakes and occurred at a much faster rate.

The research team's quest began in December 2021, when a distant quake recorded by the seismometer led to the discovery of a 150-meter-wide crater. Collaborating with the Mars Reconnaissance Orbiter, they identified a second fresh crater over 100 meters (320 feet) in diameter. However, smaller craters caused by smaller meteoroids remained elusive. By studying the spectra of marsquakes, the team identified 80 more quakes that were likely caused by meteorite strikes.

Until now, estimates of meteorite impacts on Mars relied on orbital images and models based on the moon's preserved impact craters. However, extrapolating these estimates to Mars was challenging due to the planet's stronger gravitational pull and its proximity to the asteroid belt. The researchers overcame this challenge by utilizing the seismic waves of impact, which travel through the crust and mantle and can be picked up by seismometers.

The new data provides valuable insights into the age of Mars and has implications for future missions to the planet. The density and size of meteorite craters reveal the age of different regions of Mars, with fewer craters indicating a younger surface. Knowing the exact number of impacts is crucial for the safety of robotic and human missions to Mars. For future missions, the research team plans to utilize machine learning technologies to aid in identifying craters in satellite images and seismic events in the data.

"This is the first paper of its kind to determine how often meteorites impact the surface of Mars from seismological data," said Domenico Giardini, Professor of Seismology and Geodynamics at ETH Zurich and co-Principal Investigator for the NASA Mars InSight Mission. "Such data factors into the planning for future missions to Mars."

The findings not only shed light on the frequency of meteorite impacts on Mars but also highlight the importance of seismology as a tool for measuring impact rates. This groundbreaking research opens up new avenues for understanding the Red Planet and paves the way for future exploration and scientific endeavors.

The study, titled "An estimate of the impact rate on Mars from statistics of very-high-frequency marsquakes," will be published in Nature Astronomy.