Mars' Moons Might Have Been Created From Asteroids Coming Too Close to the Red Planet

The moons of Mars, Phobos and Deimos, could have formed from the remnants of an asteroid that was destroyed by the planet's gravitational forces. Researchers from NASA and Durham University utilised advanced computer simulations to explore how such an event might have unfolded. These findings present a compelling new explanation for the origin of Mars' two small moons, which have long puzzled scientists.

A New Model for Moon Formation

According to a study published in the Icarus Journal on November 20, a large asteroid, upon straying too close to Mars, crossed the planet's Roche limit—a critical distance where tidal forces exceed an object's structural integrity—leading to its disintegration. The resulting debris, according to simulations, would have gradually coalesced into Phobos and Deimos. Dr Jacob Kegerreis, a scientist at NASA's Ames Research Center, stated in a statement that this new model offers an “exciting” alternative to previously considered theories about the moons' formation.

Phobos and Deimos are unusual among the solar system's moons. While their irregular shapes and small sizes resemble asteroids, their circular orbits, aligned with Mars' equatorial plane, suggest they formed in orbit around the planet. Previous theories, such as their origin from impact ejecta or capture of asteroids, have struggled to fully explain their characteristics.

Simulations Provide Answers

Using Durham University's supercomputers, researchers conducted hundreds of simulations, adjusting variables like the asteroid's size, speed, and proximity to Mars. The results indicated that enough fragments could have survived to create a debris disk around the planet, eventually forming the two moons. Dr Jack Lissauer of NASA Ames explained in a press release that this model allows for efficient distribution of moon-building material, even from a relatively small parent asteroid.

Future Tests with MMX Mission

The Japanese Aerospace Exploration Agency's (JAXA) Martian Moons eXploration (MMX) mission, launching in 2026, is expected to provide further insights. The mission will return samples from Phobos, which will be analysed for their composition. If similarities to Martian material are found, it may support the impact hypothesis, while asteroid-like material could validate this new model.

This research could also enhance understanding of planetary interactions with smaller celestial bodies across the solar system, opening doors to further exploration of moon and ring formation.