Ceres, the only dwarf planet in the asteroid belt, is about 1000 km in diameter, has a mass of almost 1 trillion kg and if Ceres were to impact Earth, all life on Earth would have been destroyed. But why is Ceres listed as the largest asteroid (planetoid) in books or documentaries? Ceres is a dwarf planet after all, because according to the IAU, a dwarf planet is: 1. Orbits around a star. 2. has enough gravity to have an (almost) round shape. and 3. has not cleared its orbit of other objects (is the only celestial body in its orbit around a star).
Answer
Ceres is indeed a dwarf planet, but that does not alter the fact that it is also an asteroid.
The asteroids are the many smaller objects, mainly between the orbits of Mars and Jupiter, that have not cleared their orbits (because there are still so many of them together) and therefore cannot be called a ‘planet’. Some below it, such as Ceres, are so large that they are given the status of dwarf planet.
Beyond Neptune, there is a second belt of smaller objects called the Kuiper Belt. We distinguish these objects from the asteroids because they are located elsewhere, and also because they have a slightly different composition: far from the Sun there is a lot of ice, while the asteroids are mostly pure rock chunks. Also in the Kuiper belt there are a number of objects, such as Pluto, that are large enough to deserve the name ‘dwarf planet’.
The name ‘dwarf planet’ was invented in 2006, partly as a consolation prize for Pluto, which was then disposed of as a ‘real planet’.
Answered by
prof. Christopher Waelkens
Astronomy
Old Market 13 3000 Leuven
https://www.kuleuven.be/
.