* Planets are large celestial bodies that orbit a star. They are significantly larger than asteroids.

* Comets are icy bodies that orbit the Sun. While they can be small, some comets are larger than many asteroids.

* Moons are natural satellites that orbit planets. Moons can be quite large, even larger than some planets.

* Asteroids are rocky bodies that orbit the Sun, primarily found in the asteroid belt between Mars and Jupiter. They are generally much smaller than planets, comets, or moons.

Therefore, asteroids are typically the smallest of the listed options.