New class of Mars quakes reveals daily meteorite impacts

An international team of researchers led by ETH Zurich and Imperial College London has made the first estimate of global meteorite impacts on Mars using seismic data. Their findings indicate that between 280 and 360 meteorites strike the planet each year, creating impact craters larger than 8 meters (about 26 feet) across.

Geraldine Zenhaeusern, who co-led the study, noted: “This rate was about five times higher than the rate estimated from orbital images alone. In line with orbital images, our findings show that seismology is an excellent tool for measuring impact rates.”

Seismic ‘chirp’ signals a new class of earthquakes

Using data from the seismometer deployed during the NASA InSight mission to Mars, researchers found that six seismic events recorded in the station’s vicinity had previously been identified as meteoric impacts – a process made possible by the recording of a specific acoustic atmospheric signal generated when meteorites enter the Martian atmosphere.

Now, Zenhäusern of ETH Zurich, co-leader Natalia Wójcicka of Imperial College London and the research team have discovered that these six seismic events belong to a much larger group of marsquakes, so-called very high frequency (VF) events. The source process of these quakes is much faster than a tectonic marsquake of comparable size. While a normal magnitude 3 quake on Mars lasts a few seconds, an impact-generated event of the same size lasts only 0.2 seconds or less, due to the hypervelocity of the collision. By analyzing marsquake spectra, the team identified an additional 80 marsquakes that are now thought to have been caused by meteorite impacts.

Their research mission began in December 2021, a year before dust accumulating on the solar panels ended the InSight mission, when a large, distant earthquake recorded by the seismometer sent a broadband seismic signal reverberating across the planet. Remote sensing linked the quake to a 150-meter-wide crater. To confirm, the InSight team worked with the Mars Reconnaissance Orbiter (MRO) Context Camera (CTX) to search for other new craters that would match the timing and location of the seismic events detected by InSight.

The teams’ detective work paid off, and they were fortunate to find a second fresh crater over 100 meters (320 feet) in diameter. Smaller craters, however, which were created when basketball-sized meteorites hit the planet and should be much more common, have remained elusive. Now, the number of meteorite impacts is being re-estimated based on the occurrence of these special high-frequency earthquakes.

First meteorite impact based on seismic data

About 17,000 meteorites fall to Earth every year, but unless they streak through the night sky, they are rarely noticed. Most meteors disintegrate as they enter Earth’s atmosphere, but on Mars the atmosphere is a hundred times thinner, exposing the surface to larger and more frequent meteorite impacts.

Until now, planetary scientists have relied on orbital images and models derived from well-preserved meteorite impacts on the moon, but extrapolating these estimates to Mars has proven challenging. Scientists had to take into account Mars’ stronger gravity and its proximity to the asteroid belt, both of which cause more meteorites to hit the red planet. On the other hand, regular sandstorms result in craters that are much less well preserved than those on the Moon, and therefore not as easy to detect with orbital images. When a meteorite strikes the planet, the seismic waves from the impact travel through the crust and mantle and can be picked up by seismometers.

Wójcicka explains: “We estimated the diameters of the craters based on the sizes of all VF marsquakes and their distances. We then used this to calculate how many craters there are around the InSight lander over the course of a year We then extrapolated this data to estimate the number of impacts that occur annually on the entire surface of Mars.”

Zenhäusern adds: ‘Although 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. However, the sensitive InSight seismometer was able to hear every single impact within the surface. range of the lander.”

Understanding the Age of Mars and Future Missions

Like the lines and wrinkles on our faces, the size and density of craters from meteorite impacts reveal clues about the age of different regions of a planetary body. The fewer craters, the younger the area of ​​the planet. Venus, for example, has almost no visible craters because its surface is constantly reworked by volcanism, while Mercury and the moon are heavily cratered with their ancient surfaces. Mars falls between these examples, with some old and some young regions distinguishable by the number of craters.

New data shows that an 8-meter (26-foot) crater forms somewhere on the surface of Mars almost every day, and a 30-meter (98-foot) crater forms about once a month. Because hypervelocity impacts create explosion zones that are easily 100 times larger in diameter than the crater, knowing the exact number of impacts is important for robotics safety, as well as for future human missions to the Red Planet.

“This is the first paper of its kind to use seismological data to determine how often meteorites hit the surface of Mars – which was a level one mission objective of the Mars InSight mission,” said Domenico Giardini, professor of seismology and geodynamics at ETH Zurich and co-principal investigator for NASA’s Mars InSight mission. “Such data play a role in planning future missions to Mars.”

According to Zenhäusern and Wójcicka, the next steps in advancing this research include using machine learning technologies to help researchers identify further craters in satellite images and identify seismic events in the data.