Why does mars have 2 moons and Earth has one?

Answer 1

No specific reason, that's just the way it evolved when the planets were being formed. Some planets have no moons at all, others such as Jupiter have as many as 66!

When a planet has more than one moon, it is possible that these may have been formed by the collision of an original single large moon with a foreign body, such as a huge asteroid or comet, which smashed the moon to pieces and led to the formation of two or more smaller ones.

The same thing is believed to have led to the formation of the asteroid belt that seperates the Inner from the Outer solar system- many astronomers believe that the belt of asteroids was once a planet that was destroyed in a solar collision, and the asteroids are the remaining fragments of it. The same thing may also account for the rings of Saturn.

Answer 2

Mars has two moons, Phobos and Deimos, which are likely captured asteroids. Earth's moon, on the other hand, is thought to have been formed from a collision with a Mars-sized body early in Earth's history. The difference in the number and origin of moons for Mars and Earth is due to their unique planetary histories and gravitational interactions with other celestial bodies.