Mars has two moons, Phobos and Deimos. They are believed to be captured asteroids, meaning they weren't formed alongside Mars but were pulled into its gravitational field at some point in the past.

Here's why scientists think they are captured asteroids:

* Irregular Shapes: Both moons are irregularly shaped, unlike the rounder moons of other planets, which are more likely to have formed from the same disk of material as their planet.

* Low Density: Phobos and Deimos have very low densities, more akin to asteroids than rocky moons.

* Orbit: Their orbits are not perfectly circular, and they have a slightly tilted inclination compared to Mars' equator, which is more typical of captured objects.

* Composition: Spectral analysis suggests they are composed of carbon-rich materials, similar to some asteroids.

While the captured asteroid theory is the most widely accepted explanation, there are still some unresolved questions. For example, the origin of the similar composition of Phobos and Deimos remains a subject of debate.

It's worth noting that there are also alternative theories, like the possibility that Phobos and Deimos formed from debris ejected by a massive impact on Mars. However, the captured asteroid theory is currently the most supported by evidence.