For some planets, the meteorite bombardment never stops. A new analysis of data collected by a seismometer on Mars has revealed that space rocks are hitting the red planet much more often than we previously suspected.

In fact, Mars looks like it’s taking an absolute hit. Based on the number of nearby earthquakes detected by the Mars InSight lander during the operation, the team estimates that Mars is hit by basketball-sized rocks hitting its surface almost every day.

“This figure was about five times higher than the number predicted from orbital images alone,” says planetary scientist and co-author Geraldine Zenghausern of ETH Zurich in Switzerland. “When combined with orbital imaging, our findings show that seismology is an excellent tool for measuring impact levels.”

Mars InSight’s four-year watch over the interior of Mars, before it disappears at the end of 2022, fundamentally changed our understanding of the red planet. We used to think that Mars was probably pretty boring inside; InSight revealed a range of previously overlooked tectonic and magmatic activity, as well as revealing the planet’s interior structure.

Another important point detected by the sensitive laboratory was the slight tremors of the rocks cutting the Martian crust. This has given scientists a new tool to estimate impact rates on Mars, which could help calibrate our understanding of the planet’s geological history.

The rate at which craters form on a planet’s surface can help estimate how old the surface is. Surfaces with more craters are considered older; those with less are correspondingly younger. If we know the rate at which these craters form, we can determine how old the surface is.

“By using seismic data to better understand how often meteors hit Mars and how these impacts change its surface, we can begin to build a timeline of the red planet’s geological history and evolution,” explains planetary scientist and co-author Nataliya Vuytsichka from Imperial. London College.

“It can be viewed as a kind of ‘cosmic clock’ that helps us date the surfaces of Mars and possibly other planets in the solar system beyond.”

Here on Earth, thousands of meteorites fall every year, but most of them break up in the upper atmosphere and we low-level dwellers don’t notice. Mars has an atmosphere, but it is 100 times thinner than Earth’s. This means Mars does not have the same impact protection; Stones can fall from space almost unimpeded.

Additionally, Mars is very close to the asteroid belt between its orbit and Jupiter’s orbit, so there are many rocks nearby that contribute to high impact rates.

Previous estimates of the impact rate with Mars were based on satellite imagery. Satellites orbiting Mars continually photograph the surface, recording the appearance of new craters. This is itself an imperfect quantifier of exposure, but until InSight it was the best option available.

“Although the new craters are best seen on flat, dusty terrain, where they are truly visible, such terrain covers less than half of the surface of Mars,” Zenghausen said. he explains. “But InSight’s sensitive seismometer could hear every shock within the lander’s radius.”

By counting new craters and tracking them with InSight, the researchers combined the two data sets, allowing them to calculate how many impacts occurred near the lander over the course of a year and extrapolate that to the global impact frequency.

He found that between 280 and 360 impacts occur on Mars each year, resulting in craters larger than 8 meters (26 feet) in diameter, or about one per day. Craters larger than 30 meters (98 feet) in diameter occur about once a month. This is not only important for understanding the history of Mars, but also provides valuable information that will help prepare for human exploration of the Red Planet.

“This is the first study of its kind to determine how often meteorites impact the Martian surface from seismological data – this was the goal of the first phase of the Mars InSight Mission,” says seismologist and geodynamicist Domenico Giardini from ETH Zurich. “Such data influences the planning of future missions to Mars.” The study was published on: Nature Astronomy.