In our Solar System, the moons are even more varied than the planets they accompany: there are 95 moons for JupiterJupiterthe gas giant, and more than 140 for SaturnSaturnthe ringed planet. The inner planets, orbiting closer to the Sun than the asteroid belt, have much less. If Mercury and VenusVenus evolve alone, the Earth does have a natural satellite. According to the theory most commonly accepted by scientists, our Moon was formed following a giant impact between the young Earth and a protoplanet the size of Mars. But then, what about Phobos and Deimos, the two companions of the Red Planet?
Little moons like no other
Discoveries at the end of the 19th centurye century by theastronomerastronomer American Asaph Hall in 1877, PhobosPhobos et DeimosDeimos are relatively small and irregular celestial bodies, very different from the moons of the other planets of the Solar systemSolar systemlike Earth's Moon.
Phobos, the larger of the two moons, measures a little over twenty kilometers in diameter. She orbitorbit very close to Mars, just 6,000 kilometers from the surface, making it one of the closest natural satellites of a planet in the entire Solar System. This proximity causes Phobos to undergo a rapid rotation around Mars, completing a complete revolution in less than half a Martian day. One of the most remarkable features of Phobos is its irregular shape: it resembles a piece of rock riddled with craters. In addition, it is gradually approaching Mars, at a rate of approximately 1.8 meters per century. Scientists estimate that it could lead to a collision with Mars within around 50 million years, if it is not disintegrated before then by the gravitygravity of the Red Planet.
As for Deimos, it only measures a little over a dozen kilometers in diameter. Smoother in appearance than Phobos, Deimos orbits approximately 20,000 kilometers from Mars, and circles it in around thirty hours.
With their asteroid-like appearance, these two moons continue to fuel scientists' speculations. What are Phobos and Deimos? Asteroids captured by the Martian gravitational field or debris from a giant collision with Mars? Researchers from the NasaNasa have just proposed a new possible scenario to explain the existence of these two small moons.
An ancient asteroid destroyed?
Thanks to numerous simulations carried out on supercomputerssupercomputersthe team of scientists made an interesting discovery: the two celestial bodies, Phobos and Deimos, were born from the destruction of an ancient, larger asteroid. Researchers present their results in the journal Science Direct. According to their simulations, an asteroid passing near Mars could have been destroyed by the strong gravitational attraction of the Red Planet.
The resulting rock fragments would then have dispersed into a variety of orbits around Mars. More than half of the fragments would have escaped the Martian system, while others would have remained in orbit. Torn between the gravitational pulls of Mars and the Sun, some of the asteroid debris adopt trajectories leading them to collide with each other, with each encounter spreading more debris. Over the course of the collisions, smaller debris could have organized around the planet in the form of a dust disk. According to simulations, part of this debris would subsequently have agglomerated, forming Phobos and Deimos.
Thanks to numerous simulations, NASA researchers are proposing a new scenario for the formation of Martian moons. © NASA, Jacob Kegerreis
If the simulations seem to make sense, we will have to wait until 2031, the expected date of the return of the Japanese MMX mission (Martian Moons eXploration) with samples taken from the two moons, to find out more about these two mysterious satellites.
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