In the context of astronomy, which term best describes a non-living object orbiting a planet?

The term that best describes a non-living object orbiting a planet is "satellite." In astronomy, a satellite is any object that orbits a planet or celestial body. This can include natural satellites, like moons, as well as artificial satellites, which are human-made objects launched into orbit for various purposes, such as communication, weather monitoring, and scientific research.

While asteroids and comets are also celestial bodies found in space, they do not necessarily orbit a planet. Instead, they typically orbit the Sun. A star is a massive, luminous celestial body made of plasma, and it does not fall into the category of non-living objects that orbit planets. Therefore, the choice of "satellite" specifically captures the idea of non-living objects that are in orbit around a planet.