Simulated collisions reveal how Phobos could preserve rocks blasted off Mars

Mars boasts two small moons, Phobos and Deimos, whose origins have puzzled scientists. Were these celestial bodies asteroids captured by Mars' gravity or formed from debris resulting from a massive impact on the planet? Japan's Martian Moons Exploration (MMX) mission seeks to unravel this mystery by gathering soil samples from Phobos, the larger moon.

To prepare for the mission, laboratory experiments in the United Kingdom are aiding researchers in interpreting the mission's findings. In 2023, the reporter joined the MMX mission as a participating scientist, focusing on the processes that shape the moons' surfaces, particularly impacts.

The team investigated the feasibility of foreign material being ejected from Mars and settling on Phobos through laboratory experiments and numerical simulations. Their research revealed that collisions between objects and a planetary body can deposit material on a target's surface even at relatively low impact velocities. Similar findings have been observed in material associated with impacts on asteroids Bennu and Ryugu by NASA's OSIRIS-REx and Japan's Hayabusa2 missions.

By analyzing the number and size of craters on Phobos, as well as searching for signs of foreign material, scientists aim to reconstruct the moon's impact history and gain insights into its origin. If the captured-asteroid theory is correct, the MMX mission will encounter a primitive object that formed in the outer solar system.

Conversely, if Mars underwent a giant impact, the moons might retain fragments of Martian rock and the impacting object, potentially discernible through distinct compositions in the material collected by MMX.