Where did the two natural satellites of Mars, Phobos and Deimos, come from? For a long time, their shape suggested that they were asteroids captured by Mars. However, the shape and course of their orbits contradict this hypothesis.
Two independent and complementary studies provide an answer to this question. One of these studies, to be published in The Astrophysical Journal and predominantly conducted by researchers from the CNRS and Aix-Marseille Université, rules out the capture of asteroids, and shows that the only scenario compatible with the surface properties of Phobos and Deimos is that of a giant collision.
In the second study, a team of French, Belgian, and Japanese researchers used cutting-edge digital simulations to show how these satellites were able to form from the debris of a gigantic collision between Mars and a protoplanet one-third its size. This research, which is the result of collaboration between researchers from Université Paris Diderot and Royal Observatory of Belgium, in collaboration with the CNRS, Université de Rennes 1, and the Japanese Institute ELSI, is published on July 4, 2016 in the journal Nature Geoscience. [More at links]