Dwarf Planet Definition
Dwarf planets are defined as celestial bodies that:
- Orbit around the sun.
- Have enough mass to have a (almost) round shape.
- Have cleared its orbit from other materials (as opposed to a “real” planet).
- Are not moons of planets.
Before 2006, Pluto had been considered to be a “regular” planet with the other 8 planets in our solar system. The discovery of a planet of the same size as Pluto out of the Kuiper Belt, however, put the debate on what the actual defintion for a planet and a dwarf planet is. The result of this debate emerged as a new official definition for dwarf planets, which has been in force since 24 August 2006.
What separates dwarf planets from plants, however, is point number 3: planets have cleaned their orbits using their gravity by pushing or pulling other materials. On the other hand, dwarf planets tend to intersect other celestial bodies and materials on their orbits.
The official definitions and rules for the distinctions between planets and dwarf planets are handled by the International Astronomical Union.
In connection with Pluto’s declassification from the planet to the dwarf planet in 2006, the International Astronomical Union acknowledged Pluto’s special position in the solar system and therefore chose to introduce the collective term ‘plutoid’ for all the dwarf planets that are more distant from the sun than Neptune.
Facts about dwarf planets
- Pluto: Pluto is the largest and most famous dwarf planet in our solar system.
- The first 5 recognized dwarf planets are Ceres, Pluto, Eris, Makemake and Haumea.
- Time Spans: Like the other planets, the dwarf planes vary in day-time and year-time both between themselves and the sun. This means that time units such as day and year have different values than on earth. For example, 1 year on Pluto is approx. 248 years here on Earth. 1 year at Ceres is approx. 4.6 years here on Earth.
- Kuiperbelt: Almost all dwarf planets in our solar system are found in the Kuiperbelt (also Pluto). The only dwarf planet outside the Kuiper belt is Ceres, located in an asteroid belt between Mars and Jupiter.
- Structure: Dwarf planets consist primarily of rock and / or ice. The relationship between rock and ice depends on the location of the dwarf planet in the solar system.
- Life: None of the known dwarf planets can house life (at least not the life we know).
- Atmosphere: Dwarf Plants Pluto and Eris have thin atmospheres that expand as they move closer to the sun and collapse (or freeze) as they move away from the sun.
- None of the known dwarf planets have rings.
- Moon: Many, but not all, dwarf planets have moons. Ceres has, for example, no moons where Pluto has 5 moons.
- Dawn: The first mission to a dwarf planet is the ‘Dawn’ probe, launched on September 27, 2007. Its goal was to run around Ceres in February 2015. In 2011, Dawn also visited the Vesta protoplanet. If the mission succeeds, Dawn becomes the first spacecraft that has been used in discovery of 2 space bodies.
- New Horizons: The first mission to the Kuiperbelt – where Pluto and most other dwarf planets are – is ‘New Horizons’, first launched in 2006.