Mars is subjected to almost daily meteorite impacts, with about five times more impacts than previously estimated, according to seismic recordings made on the red planet. An international team, led by researchers from the Zurich Polytechnic School (ETH) and Imperial College London, reports in the journal Nature Astronomy, published Friday, a new look at the subject, thanks to sound.
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.
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.
A probe landed on Mars in 2018
“Listening to impacts appears to be more effective than trying to see them if we want to understand how often they occur,” said Gareth Collins, co-author of the study and professor at Britain’s Imperial College, in a statement 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, landed it in November 2018 on the Martian plain of Elysium, allowing humanity to put its ear to the planet’s surface for the first time. The initial objective was to measure its internal activity and possible seismic events.
“Hear every impact”
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 ETH, in a press release from her establishment.
Identifying small meteorite craters from an orbiting probe is all the more difficult as the planet is the scene of frequent sandstorms that can mask them. “If the new craters can stand out better on flat, dusty terrain, this type of terrain only covers half the planet,” according to Géraldine Zenhäusern. The advantage of the seismograph was “being able to hear each impact within the range of the probe”.
In search of a particular acoustic wave
The team’s calculations are based on the identification of a particular type of acoustic waves, which propagate across the surface of Mars upon meteorite impact. These events, called Marsquake-VF (high frequency Mars tremors), made it possible to estimate the diameter of a crater and its distance from the probe.
Then calculate the number of craters created in one 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 with seismological data the frequency of meteorite impacts on the surface of Mars,” 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…
