Two recent studies published in Nature Geoscience and The Astrophysical Journal that attempt to find out how the Solar System formed have focused on Mars and its two enigmatic moons: Phobos and Deimos. According to these investigations, both satellites arose as a result of a brutal collision of Mars with another celestial body, probably another planet in formation. Phobos and Deimos would be the only survivors of the ten moons that were born with the impact and that over the years disappeared. The researchers also believe that in the future Deimos could be left alone, since it is the only one that maintains a stable orbit. Based on their observations, Phobos has been detected to be gradually being drawn to Mars, which could lead to its destruction.
The small size and irregular physiognomy of these two potato-like moons made scientists think for a long time that they could be asteroids captured by Mars. However, the orbits that follow around the Red Planet deny that possibility. Another hypothesis suggests that Phobos and Deimos could have formed at the same time as Mars and with the same composition, but the low density of these moons seems to undermine this theory. That is why most astrophysicists thought that they arose from a collision between Mars and a planet in formation, although they did not understand why two small moons emerged after the impact instead of a larger satellite, as happened on Earth.
The study published in The Astrophysical Journal , which has been led by scientists from the CNRS and Aix-Marseille Université1, rules out that Phobos and Deimos were asteroids captured by Mars and ensures that the only explanation that fits with the characteristics and composition of the surface of the two satellites is a spectacular collision. The second investigation, published in Nature Geoscience and carried out by a team of Belgian, French and Japanese scientists, used virtual 3D simulations to show that Phobos and Deimos were able to form from the rubble left behind by the brutal crash of Mars with a protoplanet one third its size. That collision would have occurred between 100 and 800 million years after those planets began to form. According to the researchers, the debris resulting from the collision would have created a large disk of material around Mars . The inner part would be denser and would have been composed of material merging while the outer part of the disk would be mostly gas.
In the inner part of the disk a moon would have formed a thousand times bigger than Phobos. The gravitational interactions that took place outside the disk also created other moons, smaller and more distant. Thousands of years later, Mars was surrounded by about ten small moons and one huge satellite. Several million years later, once the debris disk was already extinct, only the two furthest moons were left standing: Phobos and Deimos, which still remain. The great impact theory would also serve to explain why the Martian northern hemisphere has a lower altitude than the southern hemisphere. The Martian northern hemisphere is home to the largest known crater in the Solar System, Borealis , which probably arose from that planetary collision. That may also explain the fact that there are two satellites on Mars instead of a larger moon like ours, which was also created from a collision, in this case with an object whose mass was 10% that of the Earth. Land. The difference lies in the speed of rotation of both planets. The Earth, at that time, rotated very fast and took only 4 hours to turn on itself, while Mars did it six times slower.
In the coming years, there will be more data on the Martian moons, as the Japanese space agency, JAXA, will launch the Mars Moons Exploration (MMX) mission in 2020, which will collect samples of Phobos, bring them to Earth in 2027 and can be confirmed with satellite material if the conclusions of these studies are correct. For their part, the European Space Agency and Roscosmos plan a similar mission for 2024.
Caption: Recreation of the brutal collision from which Phobos and Deimos, the moons of Mars, were able to form. The size of the celestial body that Mars collided with must have been a third that of Mars, at that time a young planet, with a denser atmosphere and liquid water on its surface.
Credit: Copyright Université Paris Diderot / Labex UnivEarthS 2016
