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Mars Moon Mystery

Where Did Phobos Come From?


Mars has always fascinated mankind, both civilian and scientist alike. There have been assertions of extraterrestrial life on the surface, and propositions of colonizing the red planet. But one of the greatest mysteries and debates has been about the origins of its tiny moons, Phobos and Deimos.

Asteroid Capture Theory

Judging by the look of Phobos one could conclude that it may in fact be a captured asteroid.

This, therefore, is what the commonly held theory was. Phobos, like its sister moon Deimos, was likely a captured asteroid from the asteroid belt.

It is not an unlikely scenario, after all asteroids break free from the asteroid belt all the time. Collisions, gravitational perturbations and other random interactions can knock asteroids off of their normal orbits around the Sun and send them tumbling into the inner sanctum of the solar system.

Then, should one of them stray too closely to a planet, like Mars, its gravitational pull could confine it to a new orbit.

Large Impact Theory

Net everyone has been convinced of this theory however. Instead, some wondered if perhaps these moons of Mars could have formed like the Moon of Earth is purported to have formed.

While theories of our Moon's formation have abounded, the most commonly help theory, based on the best evidence we have, is that our Moon formed when a large object impacted the Earth early in its formation. This impact caused a large amount of mass to be ejected into outer space.

The Earth's gravity contained the hot, plasma-like material into a concentric orbit about the Earth.

Over time the ring of molten rock around Earth congealed together to form the satellite that we call our Moon.

So despite the look of Phobos and Deimos, some suggested that perhaps these tiny orbs formed in a similar way around mars.

Well, it turns out that they may be right.

The first indication, is that the composition of Phobos is unlike anything found in the asteroid belt. So it if was a captured asteroid, it seems that it would have have an origin other than the asteroid belt.

Perhaps the best evidence so far gathered is the presence of a mineral called phyllosilicates on the surface of Phobos. This mineral is very common on the surface of Mars, an indication that Phobos formed from the Martian substrate.

And beyond the presence of the phyllosilicates, the general mineral composition of both surfaces are in agreement.

But the composition argument isn't the only indication that Phobos and Deimos may have originated from Mars itself. There is also the question of orbit.

The near-circular orbits of the two moons are very near to Mars' equator, a fact which is difficult to reconcile in the capture theory.

Born out of Mars

So while the matter isn't yet closed, it seems that the current evidence points to the moons Phobos and Deimos having an origin of within Mars itself, having formed in a similar way in which our Moon did.

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