Mars gets walloped by space rocks way more than scientists thought


NASA's Mars Reconnaissance Orbiter captured an image of a fresh impact crater on Mars in 2013.

Watch out, Martians.

Meteorites slam into Mars five times more than planetary scientists thought, a finding published in the journal Nature Astronomy. This makes impacts on the Red Planet about a daily occurrence. A 26-foot-wide (8-meter) crater forms almost each day, and a nearly 100-foot (30-meter) crater is created once a month.

Previous estimates of these Martian impacts largely came from studying crater imagery on the moon and from Mars-orbiting craft. But unprecedented seismic data — detected by NASA’s now-defunct InSight lander — showed objects regularly impacting the surface.

“This rate was about five times higher than the number estimated from orbital imagery alone,” Géraldine Zenhäusern, a seismologist at ETH Zurich in Switzerland who co-led the research, said in a statement.

“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 added. “The sensitive InSight seismometer, however, could hear every single impact within the landers’ range.”

(And much, much larger rocks have, over millions of years, slammed into Mars: NASA estimates there are over a quarter-million impact craters about the size of Arizona’s famous Barringer Crater, which is some 4,000 feet across. And there are over 43,000 Martian craters larger than three miles wide.)

NASA’s InSight lander detected the marsquake created by this impact in December 2021.

NASA’s InSight lander detected the marsquake created by this impact in December 2021.
Credit: NASA / JPL-Caltech / University of Arizona
The Insight lander's seismometer seen on the Martian surface.

The Insight lander’s seismometer seen on the Martian surface.
Credit: NASA / JPL-Caltech

The InSight lander’s sensitive seismometer was designed to detect Martian temblors, called “marsquakes,” and it succeeded in detecting over 1,300 such quakes, including a “monster” temblor. But when a meteorite strikes Mars’ surface, the signal is distinct. “Where a normal magnitude 3-quake on Mars takes several seconds, an impact-generated event of the same size takes only 0.2 seconds or less, due to the hypervelocity of the collision,” ETH Zurich explained. “By analyzing marsquake spectra, a further 80 marsquakes were identified that are now thought to be caused by meteoroid strikes.”

Mars is far more susceptible to meteorite impacts than Earth. When objects do collide with Mars, the Martian atmosphere is just 1 percent the volume of Earth’s, meaning these space rocks are less likely to heat up and disintegrate. What’s more, the Red Planet is much closer to our solar system’s asteroid belt, a region teeming with millions of asteroids.

Understanding how impacts affect Mars is crucial for future human and robotic exploration. Impacts leave new Martian craters about every day. But that’s not the whole story. The greater “blast zones” are some 100 times bigger in diameter, which poses a risk to any potential colonists or infrastructure.

Mars is an inhospitable world today, beyond the regular meteorite strikes. The planet is 1,000 times drier than the driest desert on Earth. It has an elevated radiation environment (“about two and one-half times that in the International Space Station,” according to NASA), and provides little radiation protection from solar storms.

But we know Mars wasn’t always this way. A protective atmosphere once shielded the planet, and it harbored vigorously gushing rivers, and expansive lakes.

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