Mars moons may have been a part of something much bigger

In 2026, the Japan Aerospace Exploration Agency plans to launch the Mars Moons eXploration (MMX) mission, aiming to explore the Martian moons Phobos and Deimos and return samples from Phobos to Earth. The mission is expected to provide definitive answers about the origins of these enigmatic companions of the Red Planet.

The origins of Mars's moons have long puzzled scientists. Two main hypotheses have been proposed: that Phobos and Deimos are captured asteroids or that they formed from debris created by a massive collision with Mars. In recent studies, new model has emerged, offering a revolutionary explanation that combines aspects of both theories.

This new hybrid model suggests that, rather than a direct collision, a near miss by a large asteroid could have led to the formation of Mars's moons. If an asteroid passed close enough to Mars, tidal forces exerted by the planet could fragment the asteroid, creating a string of debris that would disperse into various elliptical orbits around Mars. This process could account for the formation of both Phobos and Deimos.

One of the challenges with the captured asteroid theory is explaining the nearly circular orbits of Phobos and Deimos. Science Alert points out that captured moons are generally expected to have more elliptical orbits, while both Martian moons orbit Mars in nearly perfect circles. Additionally, Mars's relatively weak gravitational pull makes it difficult to explain how the planet could have captured two moons that are so close and have such circular orbits.

The collision theory also faces difficulties. Debris rings from an impact tend to form close to the planet, but Deimos orbits much farther away than Phobos. While Phobos orbits close to Mars at only 6,000 kilometers from the surface, Deimos orbits at about 20,000 kilometers away, exceeding the typical distance expected for debris rings.

The new hybrid model offers a solution to these challenges. Simulations show this near-impact event would generate a series of fragments that, due to Mars's tidal forces, would settle into elliptical orbits around the planet. Over time, these orbits would stabilize, forming a debris ring capable of explaining the positions and orbits of both moons. This model provides a more comprehensive explanation compared to existing theories.

Science Alert, India Today, and TRT Haber covered the new theory, among other websites. 

This article was written in collaboration with generative AI company Alchemiq