Ceres

Ceres is the largest body in the asteroid belt, a region between the orbits of Mars and Jupiter. It is classified in two ways: as the first-numbered asteroid, (1) Ceres, and also as a dwarf planet, a type of celestial body that orbits the Sun with sufficient mass to be rounded by its own gravity but has not cleared its orbital neighbourhood of other debris.

Its diameter is approximately 940 kilometres, making it the largest object in the belt, although it is much smaller than Earth's moon. It completes one orbit of the Sun in roughly five Earth years.

Discovery and naming

It was observed at the beginning of the 19th century and was initially classified as a new planet. When many other similar bodies were found in the same region, it was reclassified as an asteroid. In 2006, when the International Astronomical Union (IAU) adopted a new definition, it was placed in the category of dwarf planets. Its name comes from the Roman goddess of agriculture.

Structure and water

Scientists estimate that Ceres consists of a rocky lower layer and an upper layer of ice and minerals mixed together. A large portion of its crust is thought to be water ice. Bright patches have been identified in deep craters on the surface, interpreted as mineral deposits left by water that once seeped through, suggesting that geological activity may still be occurring.

The Dawn mission

NASA's Dawn spacecraft reached Ceres in 2015, becoming the first spacecraft to visit a dwarf planet. Its images revealed deep craters, a tall mountain called Ahuna Mons, and bright material in the Occator crater. The mission ended in 2018 when its maneuvering fuel was depleted.