Solar system

The 2 satellites of Mars

The 2 satellites of Mars

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The planet Mars has two satellites or moons, Phobos and Deimos. They are small and spin fast near the planet. This hindered its discovery through the telescope.


Phobos has just over 27 km on the longest side. It turns 9,380 km from the center, that is, less than 6,000 km from the surface of Mars, every 7 hours. Deimos is half of Fobos and turns 23,460 km from the center in just over 30 hours.

The most outstanding feature of Phobos is the Stickney crater, which measures 10 km in diameter. Its surface is riddled with shallow grooves, which have a width between 100 and 200 meters, and a depth of 20 or 30 meters.

The small pits with raised edges, aligned in parallel formations, could be points where gas escaped from underground ice through fissures. The current Phobos satellite could then have manifested itself as a comet.

The enormous crater of Phobos was produced by a shock that was about to destroy it completely. The orbital period of Phobos is gradually reducing. Therefore, it descends to the Martian surface 9 meters per century, which means that it will end up colliding with the planet Mars in about 40 million years.

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Deimos seems to be relatively smooth when viewed from a distance. However, in reality it is dotted with small craters filled with fine materials. Its dimensions are 16x12x10 km. Unlike Phobos, Deimos does not have a single crater larger than 2.3 km in diameter.

The great resemblance of Phobos and Deimos with a certain type of asteroids suggests that Mars has captured two of them. This probability is greater if we take into account that the main planetoid belt is slightly beyond the orbit of Mars.

The disturbances generated in Jupiter could have pushed some smaller bodies towards the inner regions of the Solar System, thus favoring the process of attraction. However, the shape of the orbits of Phobos and Deimos are very regular and almost coincident with the equatorial plane of Mars, so they make this explanation unlikely.

Another hypothesis is that both satellites were born from the rupture of a single orbital satellite around Mars, as its form testifies. But even if they had emerged from a single object broken by an impact, its origins date back to billions of years.

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