Final answer:
Mars' moons, Phobos and Deimos, are likely captured asteroids, based on their shapes and surfaces similar to asteroids from the outer asteroid belt as observed by spacecraft like the Viking orbiters and Mars Global Surveyor.
Step-by-step explanation:
The origin of Mars' moons, Phobos and Deimos, is of great interest to scientists. While there have been different hypotheses over time, the prevailing theory suggests that they are captured asteroids. Evidence for this comes from their irregular, elongated shapes, heavily cratered surfaces, and composition similar to asteroids found in the outer asteroid belt.
These characteristics were observed when the Viking orbiters studied them at close range in 1977, with subsequent observations by Mars Global Surveyor cementing the idea that these moons share attributes with smaller asteroids. Other small outer moons of Jupiter and Saturn are also thought to have been captured from passing asteroids, a process that possibly occurred early in the solar system's history.