An article published in the journal “Nature Geoscience” describes a research conducted by scientists from Université Paris Diderot and Royal Observatory of Belgium, in collaboration with the CNRS, Université de Rennes 1 and the Japanese Institute ELSI on Deimos and Phobos, Mars moons, which supports the theory of an ancient impact as their origin. It’s complementary to another, independent, led by scientists of the French space agency CNRS and Aix-Marseille Université whose results will be published in “The Astrophysical Journal”.
The origin of Phobos and Deimos has been a source of discussions for a long time. They look like asteroids because of their small size and irregular shape but no one has ever been able to explain how they were captured into such circular and equatorial orbits. On the other hand, at least so far no one could explain why if the two moons were born as a result of an impact there are only two of them and so small. For example, the dwarf planet Pluto has four small moons and a proportionally huge moon probably born as a result of an impact.
Now maybe some answers can be given thanks to two different research. The one described in “Nature Geoscience” focuses on the nature and composition of the materials that make up Deimos and Phobos. The one described in “The Astrophysical Journal” focuses on the characteristics of the debris disk that formed after the ancient impact to explain the birth of the two small moons of Mars.
According to the scientists who have conducted the first research, the amount of fine-grained dust on the surface of Deimos and Phobos is excessive to be the consequence of the erosion processes caused by interplanetary dust. The best explanation is that it’s dust that has formed from the external debris and later fall on the moons. This also explains the moons’ huge porosity and low density.
According to the scientists who conducted the second research, a planetoid struck the Mars when it was between 100 and 800 million years old. The debris generated initially formed a disk and slowly merged into a large moon. They also formed other small moons, creating a situation similar to that of Pluto.
However, the big moon and most small moons have been attracted in the course of time by Mars’ gravity and crashed on the planet. Only Deimos and Phobos, the two most distant small moons, survived and even Phobos will be destroyed millions of years in the future after a slow approach.
More observations will be needed to see if these reconstructions are correct. Some of the upcoming missions to Mars in their design phase also concern its moons and in particular the one called Mars Moons Exploration (MMX) by Japan’s space agency JAXA also aims to bring back to Earth samples of Phobos. The direct exam of its materials will help to understand its origin.
