Five confirmed dwarf planets, a planetary sized object that is neither an actual planet nor a natural satellite but something in the middle that may have not completely evolved, exist in our unique Solar System. As of 2018, of the 2,945 stars confirmed to host exoplanets, 650 of which are multi-planetary systems, ours remains tied for first with most confirmed planets (8) orbiting its host star, not including dwarf planets. We share this presumably temporary honor with the star Kepler-90, located in the Draco constellation, though astronomers expect billions of other star systems to exist in the Milky Way Galaxy alone, so we may not be as special as we think. Understanding the formation of star systems is among humanity’s highest priority in our mission to explore the Cosmos. We’ve only just begun unraveling the mysteries of our own star system, many answers of which lie in the region beyond Neptune called the Kuiper Belt.
The Kuiper belt is a massive disc encompassing our Solar System consisting of small celestial bodies and the remnants of material dating back to the early formation of the system. Many ancient celestial objects reside within the Kuiper Belt, including Ultima Thule and Bennu. Objects in the Kuiper Belt are often referred to as KPOs or Trans Neptunian Objects (TNOs). Several dwarf planets inhabit the region as well, most notably Pluto. Though only five have been officially designated, potentially thousands more are predicted to exist beyond Neptune, varying in size and shape. Astronomers believe that studying these primitive planets and the region may resolve the mystery of how our Solar System and its planets formed.
The Five Dwarf Planets
Ceres is the only dwarf planet found within Neptune’s orbit. It resides in the asteroid belt between Mars and Jupiter and is the belt’s largest object. Ceres was discovered on January 1, 1801 by Giuseppe Piazzi, an Italian Catholic priest and mathematician, at the Palermo Astronomical Observatory. In March 2015, NASA’s Dawn mission entered Ceres’ orbit and continued to observe and image the planet until its mission ended on November 1, 2018.
Makemake is a dwarf planet with a surface temperature of 30K (-243 C) which indicates that the surface might be composed of methane, ethane, and nitrogen ices. It was discovered in 2005 by Michael Brown’s team and named after the Rapa Nui of Easter Island’s god of fertility and Creator of Humanity. Makemake lies around 52 AU from the Sun and orbits it every 310 years. It is the second brightest Kuiper belt object after Pluto.
Haumea Is the third largest confirmed KBO, shadowing its brethren Eris and Pluto. Originally discovered in 2004 by Mike Brown at the Palomar University, it received its dwarf planet designation in 2008 by the IAU. Haumea’s namesake refers to the Hawaiian goddess of fertility and childbirth. One third the mass of Pluto, Haumea has an elongated shape thought to be a result of some giant collision, the largest member of its so called ‘collisional family’ of large Trans-Neptunian objects. Two confirmed moons orbit Haumea, Hi’iaka and Namaka.
The first Kuiper Belt Object discovered by Clyde Tombaugh in 1930, Pluto was originally considered the ninth planet from the sun until the discovery of Eris in 2005, which led the International Astronomical Union (IAU) to introduce the term dwarf planet and designate those that qualified. Pluto remains the largest and has the second most mass of any dwarf planet in the Solar System. It is the 9th largest object directly orbiting the Sun. The five moons orbiting Pluto are Charon, Styx, Nix, Kerberos, and Hydra.
Eris is the second largest dwarf planet in the Solar System. Named after the Greek goddess of strife and discord, Eris is roughly the same size as Pluto, 1445 miles in diameter (2,326 kilometers), though about 27% greater mass, making it the most massive dwarf planet in the Solar System. Eris is the 9th most massive object orbiting our Sun, though 16th overall when factoring the seven larger Moons like Ganymede and Titan. It is located at a distance of 96 AU, nearly three times the distance of Pluto from the Sun. Eris harbors a single moon called Dysnomia (another nod to Greek mythology), named after the lawless and anarchistic daughter of Eris.