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Dwarf Planets
Dwarf Planet Facts
- The dwarf planets are Ceres, Pluto, Eris, Makemake and Haumea.
- Ceres is in the asteroid belt, a region of rocky bodies between the orbits of Mars and Jupiter.
- Pluto, Eris, Makemake and Haumea orbit in the Kuiper Belt, a region of icy bodies 2.8 billion miles (4.5 billion km) from the sun. These objects are also classified as Plutoids.
- The largest dwarf planet is Eris which is around two thirds the size of our moon.
- At its furthest point Eris orbits the sun at a distance of 14 billion km and takes 557 years to make one orbit.
- The smallest dwarf planet is Ceres which is around a quarter of the size of our moon.
- Ceres was previously classified as an asteroid.
- The dwarf planet Pluto has a very thin atmosphere consisting of nitrogen, methane and carbon dioxide.
- The largest moon of Pluto, Charon, is half the size of the former planet.
- Eris, Makemake and Haumea were discovered between 2003-2005.
When is a planet not a planet?
In 2001 the International Astronomical Union (IAU) decided to modify the definition of what constitutes a planet. These definitions were again
changed in 2003 and 2006. Now the definition of a planet is that it orbits the sun, is large enough to form a round shape and has cleared similar
objects that orbit in its neighborhood.
These new definitions meant that poor old Pluto was now no longer considered a planet. So what is Pluto now? Well it is now considered a "dwarf planet"
because even though it is large enough to have formed a round shape it has not cleared similar objects that orbit in its neighborhood.
To further complicate matters yet another definition was introduced in 2008, "plutoids", which are dwarf planets which spend most of the time outside of
Neptune's orbit.
Surface of Pluto

Dwarf Planet Eris

Dwarf Planet Pluto

Future Missions to Dwarf Planets
Dawn

Arrival: February 2015
Agency: NASA
Dawn has already completed the first part of its mission which was to study the large asteroid Vesta. It successfully entered into orbit around the asteroid in July 2011 before leaving in September 2012. The craft is now on its way to the dwarf planet Ceres and is due to arrive in February 2015. If Dawn successfully enters into orbit around Ceres it will be the first craft to orbit two separate bodies.
This audacious attempt is thanks to the crafts ion propulsion engine (pictured left), which is more fuel efficient than a conventional chemical rocket allowing it to make more maneuvers and run for longer.
The goal of the mission is to characterize the early solar system and determine how size and the presence of water influenced the evolution of planets.
New Horizons

Arrival: July 2015
Agency: NASA
NASA launched New Horizons in January 2006 thus taking advantage of a once in a life time chance to use Jupiter as a gravity assist towards Pluto.
It should arrive at Pluto in July 2015 thus becoming the first spacecraft ever to visit the planet. New Horizons will make a flyby of the dwarf planet at
a distance of 6,000 miles (9,600 km) and its moon Charon at a distance of 17,000 miles (27,000 km).
Pluto Statistics |
Diameter: 1,429 miles (2,300 km)
Average Distance from Sun: 3.6 billion miles (5.9 billion km)
Orbital Period: 248 years
Rotation Period: 6.39 days
Moons: 5
Maximum Surface Temperatures: -218C (-360F)
Minimum Surface Temperatures: -240C (-400F)
Mass: 0.22% Earth's Mass
Density: 40% Earth's Density
Atmosphere: Nitrogen, methane, carbon dioxide. Discovery Date: 1930
Average Distance from Sun: 3.6 billion miles (5.9 billion km)
Orbital Period: 248 years
Rotation Period: 6.39 days
Moons: 5
Maximum Surface Temperatures: -218C (-360F)
Minimum Surface Temperatures: -240C (-400F)
Mass: 0.22% Earth's Mass
Density: 40% Earth's Density
Atmosphere: Nitrogen, methane, carbon dioxide. Discovery Date: 1930

Ceres Statistics |
Diameter: 590 miles (950 km)
Average Distance from Sun: 257 million miles (414 million km)
Orbital Period: 4.6 years
Rotation Period: 9 hours
Moons: 0
Maximum Surface Temperatures: -37C (-35F)
Minimum Surface Temperatures: -143C (-225F)
Mass: 0.015% Earth's Mass
Density: 38% Earth's Density
Atmosphere: Unknown. Discovery Date: 1801
Average Distance from Sun: 257 million miles (414 million km)
Orbital Period: 4.6 years
Rotation Period: 9 hours
Moons: 0
Maximum Surface Temperatures: -37C (-35F)
Minimum Surface Temperatures: -143C (-225F)
Mass: 0.015% Earth's Mass
Density: 38% Earth's Density
Atmosphere: Unknown. Discovery Date: 1801

Eris Statistics |
Diameter: 1,442 miles (2,320 km)
Average Distance from Sun: 6.3 billion miles (10.2 billion km)
Orbital Period: 557 years
Rotation Period: 26 hours
Moons: 1
Maximum Surface Temperatures: -217C (-359F)
Minimum Surface Temperatures: -240C (-405F)
Mass: 0.28% Earth's Mass
Density: 46% Earth's Density
Atmosphere: Tenuous atmosphere consisting of methane. Discovery Date: 2005
Average Distance from Sun: 6.3 billion miles (10.2 billion km)
Orbital Period: 557 years
Rotation Period: 26 hours
Moons: 1
Maximum Surface Temperatures: -217C (-359F)
Minimum Surface Temperatures: -240C (-405F)
Mass: 0.28% Earth's Mass
Density: 46% Earth's Density
Atmosphere: Tenuous atmosphere consisting of methane. Discovery Date: 2005

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