Some planets never stop being bombarded by meteorites.
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 ever thought.
In fact, Mars seems to be taking an absolute beating. Based on the number of near-impact shocks captured by the Mars InSight lander during its tenure, a team of scientists estimated that Mars experiences near-daily impacts from basketball-sized rocks crashing into its surface.
“This rate was about five times higher than the number estimated from orbital images alone,” says planetary scientist and co-author Géraldine Zenhäusern of ETH Zurich in Switzerland.
“Consistent with the orbital images, our findings show that seismology is an excellent tool for measuring impact rates.”
Mars InSight revolutionized our understanding of the red planet during the four years it spent observing the interior of Mars until it gave up the ghost at the end of 2022.
We used to think that Mars was probably pretty boring inside; InSight revealed a range of tectonic and magmatic activity that had previously escaped our notice, while revealing the internal composition of the planet.
The other main thing that the sensitive laboratory recorded was the faint tremors of rocks hitting the Martian crust. This gives scientists a new tool for estimating impact rates on Mars, which in turn may help calibrate our understanding of the planet’s geological history.
The rate at which craters form on a planetary surface can help estimate how old that surface is. Surfaces with multiple craters are considered older; those with less are correspondingly younger. If we know the rate at which these craters appear, we can determine how old the surface is.
“Using seismic data to better understand how often meteorites hit Mars and how those impacts change its surface, we can begin to piece together a timeline of the geologic history and evolution of the red planet,” explains planetary scientist and co-author Natalia Wójcicka of Imperial. College London.
“You could think of it as a kind of ‘cosmic clock’ that will help us date the surfaces of Mars and perhaps, beyond, other planets in the Solar System.”
Here on Earth, thousands of meteors fall every year, but most of them disintegrate high in the atmosphere while we humble surface dwellers remain oblivious. Mars has an atmosphere, but it is more than 100 times thinner than Earth. This means that Mars does not have the same impact protection; rocks can fall from space almost unhindered.
Additionally, Mars is very close to the asteroid belt between its orbit and that of Jupiter, so there are lots of rocks around that contribute to a high impact rate.
Previous estimates of impact rates on Mars relied on satellite images. Satellites in Mars orbit continuously photograph the surface and record the appearance of new craters. This is an imperfect way of counting impacts in itself, but until InSight it was the best option available.
“While the new craters are best seen on flat and dusty terrain where they really stand out, this type of terrain covers less than half of the surface of Mars,” explains Zenhäusern. “However, the sensitive InSight seismometer heard every single impact within range of the landers.”
The researchers combined the two data sets, counted the new craters and tracked them for InSight’s detection. This allowed them to calculate how many impacts occurred near the lander over the course of a year and extrapolate that to the global impact rate.
This revealed that there are between 280 and 360 impacts on Mars each year that create a crater larger than 8 meters (26 ft), a rate of about one per day. And craters larger than 30 meters (98 feet) in diameter appear about once a month.
This is not only important for understanding the history of Mars, but also provides valuable information to help prepare for human exploration of the red planet.
“This is the first work of its kind to use seismological data to determine how often meteorites hit the surface of Mars – which was the goal of the first stage of the Mars InSight Mission,” says seismologist and geodynamicist Domenico Giardini of ETH Zurich. “Such data influences the planning of future missions to Mars.”
The research was published in Astronomy of nature.