On November 20, a team of NASA scientists published a study in Icarus proposing a groundbreaking hypothesis regarding the origins of Mars' moons, Phobos and Deimos. Contrary to previous beliefs that these moons were either captured by Mars' gravity or formed from a giant impact, the researchers suggest they originated from the remnants of an asteroid that came dangerously close to the red planet and was subsequently destroyed by Mars' gravitational forces.
The model, developed by Jacob Kegerreis and his team at NASA's Ames Research Center, utilized advanced supercomputers to simulate the close passage of an asteroid near Mars. The results indicated that the asteroid crossed the Roche limit, the distance at which a planet's tidal forces can tear apart a celestial body. This destruction would have scattered fragments into orbits around Mars, where collisions among the debris led to the formation of a rocky disk surrounding the planet.
This disk may have provided the raw material for the formation of Phobos and Deimos, the smallest and most enigmatic moons in the solar system. Kegerreis expressed excitement about exploring this new avenue for understanding the creation of these moons, which are unique in orbiting a rocky planet besides Earth.
Phobos, with a diameter of 26 km, and Deimos, even smaller at 16 km, exhibit irregular shapes and cratered surfaces, resembling captured asteroids. However, their nearly circular orbits aligned with Mars' equatorial plane challenge the notion of them being captured objects. The new model offers a plausible explanation for this orbital configuration.
Co-author Jack Lissauer noted that their hypothesis enables a more efficient distribution of material necessary for forming the moons at varying distances from Mars. Previous theories struggled to account for the different distances of Phobos and Deimos from the planet.
The research team conducted hundreds of simulations using the open-source SWIFT code and supercomputing systems from Durham University in the UK, demonstrating that sufficient fragments could survive to form a rocky disk around Mars, eventually leading to the moons' formation.
While the hypothesis requires further validation, it generates predictions about the moons' properties that can be compared with current observations. The proposed model will be tested in the coming years through the Martian Moons eXploration (MMX) mission by the Japan Aerospace Exploration Agency (JAXA), set to launch in 2026. MMX aims to collect samples from Phobos and return them to Earth for analysis.
Analysis of these samples could provide crucial insights into the moons' composition, potentially resolving the mystery of their origins. If the samples reveal traces of Martian material, it would support the impact hypothesis; conversely, a composition similar to that of an asteroid would bolster the new asteroid-derived theory.
Jacob Kegerreis emphasized that this research not only offers a new explanation for Mars' moons but also enhances our understanding of lunar formation mechanisms in general. The implications of this work extend beyond Mars, potentially shedding light on the formation of other moons and rings within the solar system.