10.3 Dwarf Planets
A dwarf planet is a celestial body within the Solar System that satisfies the following four conditions:
- It is in orbit around the Sun
- It has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (near-spherical) shape
- It has not cleared the neighbourhood around its orbit
- It is not a satellite

- Ceres, the smallest dwarf planet in the Solar System and the only one in the asteroid belt. With a diameter of about 950 km, Ceres is by far the largest and most massive body in the asteroid belt. It is spherical, unlike the irregular shapes of smaller bodies with lower gravity. The surface of Ceres is probably made of a mixture of water ice and various hydrated minerals. It may harbour an ocean of liquid water, which makes it a possibility for extraterrestrial life. Ceres may be surrounded by a tenuous atmosphere containing water vapour. Ceres, the smallest dwarf planet in the Solar System and the only one in the asteroid belt. With a diameter of about 950 km, Ceres is by far the largest and most massive body in the asteroid belt. It is spherical, unlike the irregular shapes of smaller bodies with lower gravity. The surface of Ceres is probably made of a mixture of water ice and various hydrated minerals. It may harbour an ocean of liquid water, which makes it a possibility for extraterrestrial life. Ceres may be surrounded by a tenuous atmosphere containing water vapour.

- Eris is the largest known dwarf planet in the Solar System and the ninth largest body known to orbit the Sun. It is approximately 2,500 kilometres in diameter and 27% more massive than Pluto. Eris has one moon, Dysnomia. The current distance from the Sun is 96.7 AU, roughly three times that of Pluto. With the exception of some comets, the pair are the most distant known bodies in the Solar System.

- Pluto is the second-largest known dwarf planet in the Solar System and the tenth-largest body observed directly orbiting the Sun. Originally classified as a planet, Pluto is now recognised as the largest member of a distinct region called the Kuiper belt. It is composed primarily of rock and ice and is relatively small; approximately a fifth the mass of the Earth's Moon and a third its volume. It has an eccentric orbit that takes it from 4.4 to 7.4 billion km from the Sun, and is highly inclined with respect to the planets. Pluto and its largest moon, Charon, are often treated together as a binary system.