Ceres is a dwarf planet located in the asteroid belt. It was discovered in January 1801 by the Sicilian astronomer Father Giuseppe Piazzi.
Mass: 9.43 x 1020 kg
Composition: Rock and Ice
Orbit: Between Mars and Jupiter
Ceres is the smallest of the group of dwarf planets in the Solar System which also includes Pluto, Eris and Haumea. While searching for objects between Mars and Jupiter, Father Giuseppe Piazzi spotted Ceres, which was at first referred to as a planet, but was later designated an asteroid. It was not until 2006 that Ceres was described as a dwarf planet due to its similarities to a planet rather than an asteroid.
Johannes Kepler and Johann Elert Bode both suggested the idea that there were undiscovered planets lying between the then already known planets of Mars and Jupiter. While plans for a coordinated search by a large group astronomers were being formulated, Piazzi, who was to be invited to join in with the search, found Ceres. Ceres takes its name from the Roman goddess of harvest.
In common with some of the other dwarf planets, the designation of Ceres has been reclassified several times. As Johann Elert Bode had been expecting a planet to be found in the vicinity where Ceres was, it was immediately given the status of a planet. As more objects began to be observed in the same orbital area, they were thought to be remarkably similar to Ceres and so it was decided that they would all be known as asteroids, meaning star-like.
In 2006, the discovery of Eris and Makemake led to a clarification being sought from the International Astronomical Union as to the true definition of a planet. As a result of this discussion, Makemake and Eris were classified as dwarf planets. Because Eris is bigger than Pluto, Pluto was downgraded from a planet to a dwarf planet. Ceres was also classified as a dwarf planet.
The composition of Ceres is made up of a rocky core, a water-ice mantle and a thin crust. There is evidence to suggest that there is natural liquid water below the surface. This is due to the presence of water-bearing minerals on the surface. Similar to the terrestrial planets – the planets closest to the Sun – Ceres is more dense at its core than on its surface. The term used to describe this is ‘differentiated interior’. Asteroids, which are abundant in this part of the Solar System, do not have this quality.
Ceres orbits between Mars and Jupiter and is the largest object in the asteroid belt. It is not very bright and cannot be seen easily without a telescope. The best images of Ceres have been obtained by the Hubble Space Telescope.