Mars gets hit by hundreds of basketball-size space rocks every year

By Ashley Strickland, CNN

(CNN) — Hundreds of basketball-size space rocks slam into Mars each year, leaving behind impact craters and causing rumblings across the red planet, according to new research.

Mission planners could use the revelations, recorded in data collected by a now-retired NASA mission, as they determine where to land future robotic missions as well as astronaut crews on the red planet.

NASA’s InSight mission ended when the stationary lander lost a battle to an accumulation of Martian dust on its solar panels in December 2022, but the wealth of data the spacecraft collected is still fueling new research.

The lander carried the first seismometer to Mars, and the sensitive instrument was able to detect seismic waves that occurred thousands of miles away from InSight’s location in Elysium Planitia, a smooth plain just north of the planet’s equator.

During its time on Mars, InSight used its seismometer to detect more than 1,300 marsquakes, which take place when the Martian subsurface cracks due to pressure and heat.

But InSight also captured evidence of meteoroids as they crashed into Mars.

Meteoroids are space rocks that have broken away from larger rocky bodies and range in size from dust grains to small asteroids, according to NASA. Known as meteoroids while still in space, they are termed meteors as they streak through the atmosphere of Earth or other planets.

Scientists have questioned why more impacts haven’t been detected on Mars because the planet is located next to our solar system’s main asteroid belt, where many space rocks emerge to hit the Martian surface. The Martian atmosphere only has 1% of the thickness of Earth’s atmosphere, meaning that more meteoroids zip through it without disintegrating.

A meteoroid hit the Martian atmosphere on September 5, 2021, and then exploded into at least three shards, each one leaving behind a crater on the red planet’s surface. And it was just the beginning.

Searching for fresh craters

Since 2021, researchers have pored over InSight’s data and determined that space rocks bombard Mars more frequently than previously thought, as much as two to 10 times higher than previous estimates, according to a new study published Friday in the journal Science Advances.

“It’s possible Mars is more geologically active than we thought, which holds implications for the age and evolution of the planet’s surface,” said lead study author Ingrid Daubar, an associate professor of Earth, environmental and planetary sciences at Brown University, in a statement. “Our results are based on a small number of examples available to us, but the estimate of the current impact rate suggests the planet is getting hit much more frequently than we can see using imaging alone.”

The team identified eight new impact craters created by meteoroids from InSight’s data that orbiters circling the planet did previously spot. Six of the craters were near InSight’s landing site, and two of the distant impacts were some of the largest ever detected by scientists observing the red planet, according to the study.

Each of the two large impacts left behind craters about the size of football fields, and they occurred 97 days apart.

“This size impact, we would expect to happen maybe once every couple of decades, maybe even once in a lifetime, but here we have two of them that are just over 90 days apart,” Daubar said. “It could just be a crazy coincidence, but there’s a really, really small likelihood that it’s just coincidence. What’s more likely is that either the two big impacts are related, or the impact rate is a lot higher for Mars than what we thought it was.”

The team compared data collected by InSight with that taken by NASA’s Mars Reconnaissance Orbiter to zero in on where the impacts occurred. Before-and-after images enabled the team to confirm eight of the craters. It’s possible that InSight registered more impacts during its mission, and the team plans to continue searching through the data and looking for orbital evidence of fresh craters.

“Planetary impacts are happening all across the solar system all the time,” Daubar said. “We’re interested in studying that on Mars because we can then compare and contrast what’s happening on Mars to what’s happening on the Earth. This is important for understanding our solar system, what’s in it and what the population of impacting bodies in our solar system looks like — both as hazards to the Earth and also historically to other planets.”

Following seismic signals

A companion paper, published Friday in the journal Nature Communications, also explored seismic events recorded by InSight to determine that meteoroids about the size of a basketball crash into Mars on almost a daily basis.

Between 280 and 360 meteoroids hit the red planet each year, and they form impact craters larger than 26 feet (8 meters) across, according to the study. Larger craters spanning 98 feet (30 meters) occur about once a month, the study authors said.

“This rate was about five times higher than the number estimated from orbital imagery alone,” said co-lead study author Dr. Géraldine Zenhäusern, staff of professorship for seismology and geodynamics at Switzerland’s ETH Zürich, in a statement. “Aligned with orbital imagery, our findings demonstrate that seismology is an excellent tool for measuring impact rates.”

By analyzing seismic events traced to meteoroids, the team has identified about 80 marsquakes recorded by InSight that may have been caused by impacts. The marsquakes as a result of meteoroid impacts occur at a higher frequency and have a shorter duration than other marsquakes caused by subsurface activity.

“While new craters can best be seen on flat and dusty terrain where they really stand out, this type of terrain covers less than half of the surface of Mars,” Zenhäusern said. “The sensitive InSight seismometer, however, could hear every single impact within the landers’ range.”

Seismic data of the slightest ground movements on Mars could be the most direct way to understand just how many impacts occur on Mars, the researchers said.

“By using seismic data to better understand how often meteorites hit Mars and how these impacts change its surface, we can start piecing together a timeline of the red planet’s geological history and evolution,” said co-lead study author Dr. Natalia Wojcicka, research associate at Imperial College London’s department of Earth science and engineering, in a statement. “You could think of it as a sort of ‘cosmic clock’ to help us date Martian surfaces, and maybe, further down the line, other planets in the Solar System.”

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