Mars could experience more than twice as many close encounters with potentially dangerous asteroids as Earth, according to a new study. This could jeopardize exploratory missions to the Red Planet, but also provide insight into how the inner solar system formed.
Asteroids pose the greatest threat from space to our planet – 2013 Chelyabinsk meteorfor example, it generated shock waves that injured over 1,000 people and caused over $33 million in infrastructure damage.
Astronomers and citizen asteroid hunters have found about 33,000 similar space rocks that whiz close to Earth during their orbit around the sun. Some are huge—more than 460 feet (140 meters) in diameter—and orbit on paths that approach Earth’s orbit at distances of less than 0.05 astronomical units (AU). (For reference, 1 AU is about 93 million miles, or 150 million kilometers ― the average distance between Earth and the sun.) Tracking such potentially dangerous asteroids (PHAs) is a key component of planetary protection programs.
Neighboring Mars should be worse, as it lies right next to the main belt, a planet-free stretch of rocky debris between the orbits of Mars and Jupiter. But exactly how many asteroids pass by Mars is not clear. That could be a problem, study co-author Yufan Fane Zhou, a doctoral student in astronomy at Nanjing University in China, told Live Science in an email; Mars hosts many ongoing missions and May be home to human colonies someday.
To test whether people on the Red Planet would be at greater risk of potentially devastating impacts, Zhou and his colleagues at Nanjing University analyzed how many asteroids come close to Mars. They called these space rocks “CAPHAs,” an acronym for “Close Approach Potentially Hazardous Asteroids.”
To determine the number of CAPHAs on Mars, the team used computer models to simulate the motion of all eight planets and about 11,000 randomly selected asteroids in 100 million years. All of these asteroids started out in the main belt. Then, by looking at each asteroid’s proximity to six known gaps — asteroid-poor areas within the main belt where runaways could potentially slip through — the team classified about 10,000 asteroids as “near-gap.”
Connected: Hundreds of black ‘spiders’ spotted in mysterious ‘Inca City’ on Mars in new satellite images
During the simulations, the researchers made the asteroids move away from or toward the sun. This drift occurs due to Yarkovsky effect, a force generated when the sunlit surfaces of asteroids reradiate the energy they receive, acting like mini-thrusters. Simulating this drift is critical because over millennia it causes asteroids near the gap to meander into the gaps. Once there, periodic gravitational tugs from Jupiter or Saturn distort the paths of these asteroids, sending them on potential collision courses with the inner planets.
The simulations revealed that each Earth year, about 52 large asteroids wander dangerously close to Mars — about 2.6 times the 20 or so that approach Earth annually. Although these asteroids come closer to Mars than terrestrial CAPHAs do to our planet, they also travel more slowly.
NASA missions may have already witnessed the effects of some of these asteroids hitting Mars; a meteorite impact on December 24, 2021, triggered a magnitude 4 earthquake that was captured by NASA’s Mars InSight lander.
Although Zhou was ambivalent about whether near-Mars objects could affect current missions, he noted that in the future, “as human visits to Mars become more frequent, the threat posed by Mars-CAPHA may increasingly to be taken seriously.”
Still, Mars-CAPHAs can be informative for astronomers as well. “Asteroids around Mars can also deepen our understanding of the Martian environment, interactions between asteroids and planets, and the evolutionary history of the inner solar system,” Zhou said. In fact, Zhou and his colleagues suggest that at least two of these CAPHAs may even be visible from Earth in early 2025, when Mars will lie in line with Earth while orbiting on the same side of the sun.
The research was published online May 9 in the journal Monthly Notices of the Royal Astronomical Society: Letters.
