Before answering this interesting question, it is worth defining what a dwarf planet is and what distinguishes it from a full-fledged planet.
The Larousse defines a dwarf planet as a ” star analogous to a planet, but of insufficient mass to have eliminated any body likely to move around its star in a close orbit” . As its name implies, a dwarf planet is smaller than a planet, but larger than a single body.
To fully answer the question, the International Astronomical Union (IAU) recognizes the existence of five dwarf planets in our solar system. However, others may be added to the list one day. In order to complete my answer, I will make a brief presentation of each of them.
1 / Ceres.
It is the smallest of the five recognized dwarf planets. Unlike the others, it is the only one located in the main asteroid belt, which extends for memory between Mars and Jupiter. Ceres is also the most massive object and is also considered an asteroid as such.
Discovered by accident in Palermo (Sicily) in 1801, it is named after the Roman goddess of agriculture and harvest Ceres, the equivalent of Demeter in Greek mythology.
Its rotation period is 9 hours 04 minutes and it orbits the Sun in just over 4.5 years.
2 / Pluto.
Universally known, Pluto was considered, from its discovery in 1930 to the creation of the concept of “dwarf planet” in 2006, as being a planet.
Nestled in the Keiper belt, it is the largest of the five dwarf planets with a diameter of 2,370 km (against only 974 km for Ceres). Pluto has x five satellites. The first is Charon, which has a diameter of just over half of its planet (1,200 km)! Moreover, Pluto-Charon is sometimes considered to be a dual system. The other moons are much smaller: Styx, Nix, Kerberos and Hydra.
Pluto’s surface is mostly composed of methane and nitrogen.
Its rotation period is 6 days 9 hours and 17 minutes and it orbits the Sun in about 248 years.
3/ Haumea.
Discovered in 2004 in the United States, Hauméa takes its name from the Hawaiian goddess of fertility. It is characterized by its elongated shape and is the only planet to have a system of rings.
Haumea has two moons: Hiʻiaka and Namaka.
Its rotation period is only 4 hours and it orbits the Sun in about 283 years.
4 / Makemake.
Artist’s picture
The third largest dwarf planet, Makemake takes its name from the creator god of the Rapanui, a local population of Easter Island (the dwarf planet having been discovered by the United States on March 31, 2005, i.e. at the time of the Christian feast ).
This dwarf planet is about two-thirds the diameter of Pluto.
MakeMake has a single known moon of almost 200 km, which is MK2.
Its rotation period is about 23 hours and it orbits the Sun in about 306 years.
5 / Eris.
Another trans-Neptunian object, Eris is the second largest dwarf planet (2,326 km in diameter, against 3,270 for Pluto) but the most massive in the solar system. Discovered in 2005, like Pluto it has a natural satellite: Dysnomia.
For information, Eris is the farthest dwarf planet from the Sun: it is three times farther from the star than Pluto! The dwarf planet takes its name from Eris, the Greek goddess of discord.
Its rotation period is about 26 hours and it orbits the Sun in about 559 years.
Other probable planets /
There are undoubtedly other dwarf planets, some of which are in some way candidates for this status:
- Orcus, located in the Keiper Belt. With a diameter of 910 km, Orcus orbits our star in 245 years. Vanth is its only known satellite.
- Salacia, located in the Keiper belt. With a diameter of nearly 850 km, it revolves around the Sun in 274 years. Actea is its only known moon.
- Quaoar, located in the Keiper belt. It is 1,100 km in diameter, half that of Pluto. With a single known moon Weywot, Quaoar orbits the Sun in 283 years.
- Gonggong, located in the scattered disc. It is 1,200 km in diameter and has only one known moon, Xiangliu. Gongong revolves around the Sun in 554 years.
- Sedna, located in the outer reaches of the Solar System. With a diameter possibly around 1,000 km, Sedna orbits our star in about 11,400 years! It has a reddish tint.
And other smaller ones as well!