Dwarf planets are celestial bodies that are spherical and orbit the Sun, but have not cleared their orbit of debris. Ceres, Pluto, and Eris are the only recognized dwarf planets, but there may be up to 200 more in the solar system. Objects smaller than dwarf planets are called small bodies, including comets and asteroids. There are several potential dwarf planet candidates that need further study, including trans-Neptunian objects and large asteroids like Vesta, Pallas, and Hygiea.
A dwarf planet is a new category of celestial bodies created by the International Astronomers Union in 2006. It includes celestial bodies massive enough to be spherical, orbiting the Sun, that are not satellites. The crucial factor that divides a planet from a dwarf planet is that a planet must have succeeded in clearing the area of its orbit of debris and other objects, while a dwarf planet has not.
When the dwarf planet category was created, three bodies were immediately classified as such: Ceres, the largest asteroid, now a dwarf planet; Pluto, in the Kuiper belt, demoted from planetary status; and Eris, a scattered disk object located well beyond the orbit of Pluto. It was the discovery of Eris that in part prompted the International Astronomers Union to define more precisely what they meant by the word “planet”.
Despite the “dwarf planet” name, dwarf planets are not considered a subset of planets, but rather in an entirely different category. Objects even smaller than dwarf planets, for example, those lacking enough mass to be spherical, are called small bodies in the solar system, which includes comets and asteroids.
Although only three dwarf planets have been recognized, astronomers suspect there are as many as 200 in the far reaches of the solar system. There are numerous potential dwarf planet candidates that need to be studied more closely to confirm their status. For a celestial body to be approximately spherical it requires a diameter of at least 400 km. The smallest spherical body known today is the moon Mimas.
There are a number of trans-Neptunian objects with diameters greater than 400 km: Varuna, Orcus, Ixion, Quaoar, 2003EL61, 2005FY9 and many others. While we can estimate their diameter, it is more difficult to estimate whether or not they are approximately spherical. This will require more powerful telescopes. There are also several large asteroids that may be dwarf planets: Vesta, Pallas and Hygiea, the second, third and fourth largest asteroids after Ceres.
Protect your devices with Threat Protection by NordVPN
