Hundreds of basketball-sized space rocks hit Mars every year

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Hundreds of basketball-sized space rocks crash into Mars every year, leaving impact craters and causing rumbling across the Red Planet, according to a new study.

Mission planners could use these revelations, recorded in data collected by the now-retired NASA mission, to decide where to land future robotic missions or astronaut crews on Mars.

NASA’s InSight rover ended its mission in December 2022 after losing its battle with Martian dust accumulating on its solar panels, but the vast amount of data the rover collected continues to power new research.

The lander delivered the first seismometer on Mars, a sensitive instrument that could detect earthquake waves occurring thousands of miles away from InSight’s location on Elysium Planitia, a smooth plain just north of the Martian equator.

During its time on Mars, InSight used its seismometers to detect more than 1,300 Marsquakes, which occur when pressure and heat crack the Martian underground.

However, InSight also captured evidence of a meteorite impacting Mars.

According to NASA, meteoroids are space rocks that break off from larger rocky objects and can range in size from dust grains to small asteroids. They are called meteoroids while in space and are called meteors when they cross the atmosphere of Earth or other planets.

Scientists have wondered why more impacts have not been detected on Mars, since it sits next to the solar system’s main asteroid belt, where many space rocks impact the planet’s surface. The Martian atmosphere is only 1% as thick as Earth’s, meaning more meteorites get through without breaking up.

On September 5, 2021, a meteorite struck the Martian atmosphere and exploded into at least three pieces, each leaving a crater on the surface of the Red Planet. And that was just the beginning.

Researchers have been sifting through InSight’s data since 2021 and have concluded that space rocks hit Mars more frequently than previously thought, anywhere from two to 10 times more frequently than previously estimated, according to a new study published Friday in the journal Science Advances.

“Mars may be more geologically active than we thought, which could affect the age and evolution of its surface,” Ingrid Dover, an associate professor of Earth, environmental and planetary sciences at Brown University and lead author of the study, said in a statement. “Although our findings are based on the few examples we have available, current estimates of the impact rate suggest that Mars is undergoing impacts much more frequently than images alone would suggest.”

Using InSight’s data, the team identified eight new impact craters from meteorites previously spotted by spacecraft orbiting Mars. Six of the craters are close to InSight’s landing site, and two of the more distant impacts are among the largest ever found by Martian scientists, according to the study.

The two massive impacts, each leaving a crater the size of a football field, occurred 97 days apart.

“An impact of this magnitude would probably be expected to occur once every few decades, or even once in a lifetime, but here we have two, just over 90 days apart,” Dover says. “It could just be a coincidence, but that is extremely unlikely. More likely, either the two large impacts are related, or the impact rate on Mars is much higher than we thought.”

The team compared data collected by InSight with data taken by NASA’s Mars Reconnaissance Orbiter to narrow down where the impact occurred. From images taken before and after the impact, the team was able to identify eight craters. InSight likely recorded more impacts during its mission, and the team will continue to examine the data to look for orbital evidence of new craters.

“Planetary impacts happen all the time, all over the solar system,” Dover said, “and we’re interested in studying them on Mars so we can compare and contrast what’s happening on Mars with what’s happening on Earth. This is important for understanding the solar system, what’s in it, and what the population of objects that impact the solar system are like — not just as a hazard to Earth, but historically to other planets as well.”

A related paper published Friday in Nature Communications also looked at seismic activity recorded by InSight and found that basketball-sized meteorites strike Mars almost daily.

The study found that between 280 and 360 meteorites strike Mars each year, creating impact craters larger than 26 feet (8 meters) in diameter. Larger craters, up to 98 feet (30 meters) in diameter, occur about once a month, the study authors said.

“This rate was about five times higher than estimated from orbital images alone,” co-lead investigator Dr. Geraldine Zennhuisarn, professor of seismology and geodynamics at ETH Zurich in Switzerland, said in a statement. “Together with the orbital images, our results show that seismology is an excellent tool to measure impact rates.”

By analyzing meteorite-induced seismic events, the team determined that about 80 Marsquakes recorded by InSight could have been triggered by meteorite impacts. They occur more frequently and last shorter than other Martian earthquakes caused by subsurface activity.

“The new crater is best visible in the flat, dusty terrain that covers less than half of Mars’ surface,” Sennhuehn said, “but the sensitive InSight seismometer was able to hear every impact within range of the lander.”

The researchers said seismic data, which captures tiny ground movements on Mars, could be the most direct way to understand how much impact activity is happening on the Red Planet.

“By using the seismic data to better understand how often meteorites hit Mars and how these impacts alter its surface, we can begin to piece together a timeline of the Red Planet’s geological history and evolution,” co-lead author Dr Natalia Wojcicka, a research fellow in the School of Geosciences and Engineering at Imperial College London, said in a statement. “This can be thought of as a kind of ‘cosmic clock’ that can help us date the surface of Mars, and potentially other planets in the solar system.”