Mars is subject to almost daily meteorite falls, with around five times more impacts than previously estimated, according to seismic recordings taken on the red planet. Until now, we estimated the frequency of these impacts with models combining observations of meteorite craters on the Moon and images of the Martian surface taken by orbiting probes.
We adjusted these models to the characteristics of the red planet. Much more massive than the Moon, and much closer to the solar system’s main asteroid belt, Mars is a prime target for large rocks wandering through space. Furthermore, almost devoid of atmosphere – its own is a hundred times thinner than that of the Earth – it cannot even count on this protective shield to disintegrate some of the meteorites.
An international team led by researchers from the Zurich Polytechnic School (ETH) and Imperial College London provide a new perspective on the subject in the journal “Nature Astronomy” published Friday, using sound. “It seems more effective to listen to impacts than to try to see them if we want to understand how often they occur,” said Gareth Collins, co-author of the study and professor at the British Imperial College, in a press release from his institution.
And what could be better than the SEIS seismograph (Seismic Experiment for Internal Structure), an instrument produced under the supervision of CNES (National Center for Space Studies). A NASA probe, InSight, deposited it in November 2018 on the Martian plain of Elysium, allowing humanity for the first time to press its ear against the ground of the planet. The initial objective being to measure its internal activity and possible seismic events.
The team of researchers used this data to determine that the planet is hit each year by 280 to 360 meteorites creating craters at least eight meters in diameter. “This rate is five times higher than the number estimated from images taken in orbit alone,” explains Géraldine Zenhäusern, researcher at the ETH, in a press release from her establishment.
Identifying small meteorite craters from an orbiting probe is all the more difficult because the planet is the scene of frequent sandstorms that can obscure them. “While new craters may stand out better on flat, dusty terrain, that kind of terrain only covers half the planet,” Zenhäusern said. The advantage of the seismograph was that “we could hear every impact within range of the probe.”
The team’s calculations are based on the identification of a particular type of acoustic waves, which propagate on the surface of Mars when the meteorite impacts. These events, called Marsquake-VF (high-frequency Marsquakes), made it possible to estimate the diameter of a crater and its distance from the probe. Then to calculate the number of craters created in a year within a certain radius around the probe, before extrapolating this data to the scale of the planet.
“This is the first study of this kind to determine the frequency of meteorite impacts on the surface of Mars using seismological data,” notes ETH Professor Domenico Giardini. Data “to be taken into account in planning future missions to Mars”, according to him. The planet is struck approximately every month by a meteorite creating a crater at least 30 meters in diameter…
