Mars is more prone to devastating asteroid impacts than we thought, new study hints

Mars may face more than twice as many close encounters with potentially dangerous asteroids as Earth does, according to a new study. This could imperil exploratory missions to the Red Planet, but also provide insight into how the inner solar system formed. 

Asteroids constitute the biggest threat from space to our planet — the 2013 Chelyabinsk meteor, for example, generated shock waves that injured over 1,000 people and caused more than $33 million in damage to infrastructure. 

Astronomers and citizen asteroid hunters have detected around 33,000 similar space rocks that whiz closely past Earth during their orbit of the sun. A fraction of them are huge ― more than 460 feet (140 meters) in diameter ― and whirl on paths that approach Earth's orbit at distances of less than 0.05 astronomical unit (AU). (For reference, 1 AU is around 93 million miles, or 150 million kilometers ― the average distance between Earth and the sun.) Tracking such potentially hazardous asteroids (PHAs) is a key component of planetary defense programs. 

Neighboring Mars should have it worse, since it lies right next to the main belt — a planet-free stretch of rocky debris between the orbits of Mars and Jupiter. But precisely how many asteroids swing past Mars isn’t clear. This 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 current missions and may be home to human colonies someday.

To test whether humans on the Red Planet would be more at risk of potentially devastating impacts, Zhou and colleagues at Nanjing University analyzed how many asteroids make close approaches to Mars. They dubbed these space rocks "CAPHAs," an acronym for "close approach potentially hazardous asteroids." 

To determine the number of Mars CAPHAs, the team used computer models to simulate the movement of all eight planets and around 11,000 randomly chosen asteroids over 100 million years. All of these asteroids started out in the main belt. Then, looking at each asteroid's proximity to six known gaps — asteroid-poor zones within the main belt where runaway rocks could potentially slip out — the team classified about 10,000 asteroids as "near-gap." 

Related: Hundreds of black 'spiders' spotted in mysterious 'Inca City' on Mars in new satellite photos