Meteorites hit Mars almost every day, scientists discover

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Scientists have made an exciting discovery about Mars: basketball-sized meteorites hit the planet nearly every day!

Using data from a seismometer deployed during NASA’s InSight Mission, researchers estimated that between 280 to 360 meteorites strike Mars each year, creating craters larger than 8 meters (about 26 feet) across.

This discovery is significant because it’s about five times higher than what scientists previously estimated using only images from orbiting satellites. Géraldine Zenhäusern from ETH Zurich, who co-led the study, said, “Our findings demonstrate that seismology is an excellent tool for measuring impact rates.”

A New Class of Quakes

The researchers found six seismic events recorded by the seismometer that had previously been identified as meteorite impacts.

These impacts were detected because they generated specific acoustic signals when meteorites entered Mars’ atmosphere. Now, the research team has discovered that these six events are part of a larger group of high-frequency marsquakes.

These quakes occur much faster than regular tectonic marsquakes. While a normal magnitude 3-quake on Mars takes several seconds, an impact-generated quake of the same size takes only 0.2 seconds or less due to the high-speed collision.

By analyzing the marsquake spectra, researchers identified 80 additional marsquakes likely caused by meteorite strikes.

The research began in December 2021, when a large distant quake recorded by the seismometer produced a seismic signal across Mars. Using remote sensing, the quake was associated with a 150-meter-wide crater.

To confirm, the InSight team worked with the Mars Reconnaissance Orbiter (MRO) Context Camera (CTX) to find other fresh craters matching the timing and location of the seismic events detected by InSight. They successfully found a second fresh crater over 100 meters (320 feet) in diameter. Smaller craters, formed by basketball-sized meteoroids, remained harder to detect.

Approximately 17,000 meteorites fall to Earth each year, but most disintegrate in our atmosphere. Mars, with an atmosphere 100 times thinner than Earth’s, is exposed to larger and more frequent meteorite strikes.

Until now, scientists used orbital images and models from the Moon’s well-preserved meteorite impact craters to estimate Mars’ impact rate.

This was challenging due to Mars’ stronger gravitational pull and its proximity to the asteroid belt, which result in more meteorite strikes.

Additionally, Mars’ regular sandstorms make its craters less well-preserved and harder to detect with orbital imagery.

When a meteorite hits Mars, the seismic waves travel through the planet’s crust and mantle, picked up by seismometers. This provides a new way to measure Mars’ impact rate.

“We estimated crater diameters from the magnitude of all the VF-marsquakes and their distances, then used it to calculate how many craters formed around the InSight lander over a year,” said Natalia Wójcicka from Imperial College London.

They extrapolated this data to estimate the annual number of impacts on Mars’ surface.

Meteorite craters reveal clues about the age of different regions of a planet. Fewer craters mean a younger surface.

Mars has both old and young regions, distinguishable by the number of craters. The new data shows an 8-meter crater forms somewhere on Mars nearly every day, and a 30-meter crater forms about once a month.

Knowing the exact number of impacts is crucial for the safety of robotic and future human missions to Mars.

“This is the first paper to determine how often meteorites impact Mars using seismological data,” said Domenico Giardini, professor of seismology and geodynamics at ETH Zurich.

The next steps in this research involve using machine learning to identify more craters in satellite images and seismic events in the data.

The researchers’ work is published in four papers in Nature Astronomy, Science Advances, Science, and Nature Geoscience.