Mars Might Have An Asteroid Problem

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Astronomers have been surveying the sky for years to catalog and track so-called Near-Earth Objects (NEOs) , asteroids and comets that come near to or cross paths with our planet's orbit. Humanity has even been preparing for the possibility of protecting ourselves against a catastrophic collision; for example, the recent Double Asteroid Redirection Test (DART) mission nudged the asteroid Dimorphos in 2022 to prove our technology could help deflect a problematic space rock.

But, asteroids are all over the solar system, not just near Earth. Naturally then, other planets must have close encounters with—or even impacts from—wayward bits of cosmic rubble, too. Of particular interest is our neighbor planet, Mars, as we plan to send humans there in the coming decades. A new research paper accepted to the Monthly Notices of the Royal Astronomical Society Letters takes a look at asteroid threats to the red planet, and finds about two-and-a-half times more potentially hazardous asteroids at Mars than on Earth.

When you think about it, this actually makes intuitive sense. Mars is much closer to the asteroid belt–our solar system's main reservoir of rocky debris–than Earth. Of course something closer to the source would encounter more strays. "It is well known that the number of Mars crossers is larger than the number of Earth crossers," adds Alessandro Morbidelli , an astronomer at the French Observatoire de la Côre d'Azur, not affiliated with the new work.

This research team specifically investigated potentially hazardous asteroids, or PHAs . These are a subset of NEOs (or in their case, NMOs—Near-Mars Objects) that are both big enough to be a problem, and on a path that closely grazes the planet in question. "We speculate that there are more [potentially hazardous] asteroids around Mars than around Earth, and numerical simulations in our work confirm this speculation," explains Yufan Zhou, lead author and astronomer at Nanjing University. According to their simulations, there are almost 17,000 PHAs that could skim past Mars, but only about 4,700 such asteroids around Earth.

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