Dwarf Planets

By Mackenzie and Ashley

What is a dwarf planet?

There are four requirements a dwarf planet has to meet in order to be classified as a dwarf planet.

1) It must orbit around the sun.

2) It must have enough mass to assume a round shape.

3) It has not cleared its orbital path.

4) It can not be a moon.

Dwarf planets are generally smaller than Mercury. Currently, there are six objects being considered whether or not to be classified as a dwarf planet.


  • There may be as many as 10,000 dwarf planets.

  • No dwarf planet can support life as we know.

  • No known rings around any dwarf planet.

  • Not all but some dwarf planets have moons.

  • Some dwarf planets like Eris and Pluto have atmospheres that expand when they are closer to the sun, and collapse as they get further away.

  • Dwarf planets are made of solid rock and ice. Where they are located in the solar system depends on how much rock and ice it has.

  • Time on dwarf planets can greatly vary.

  • The odd tilt of Uranus is probably caused by a collision with a dwarf planet.

  • Dwarf planets share their orbital space with other objects similar to their size.

Where are dwarf planets located?

Most dwarf planets are located in the Kuiper Belt. The Kuiper Belt is a far region consisting of frozen objects. Astronomers believe that there could be up to 200 dwarf planets in the Kuiper Belt. But, there is an exception. Ceres is a dwarf planet that is located in the Asteroid Belt between Mars and Jupiter. Pluto, Eris, Makemake, and Haumea are called plutoids while Ceres is called an asteroidal dwarf planetoid. A plutoid is a dwarf planet that orbits outside of Neptune and plutoids are often called ice dwarfs because of their tiny size and cold temperatures.


A few missions on the topic of dwarf planets are New Horizon and Dawn. Currently New Horizon is on its way to Pluto. The first mission to a dwarf planet was named Dawn and the missions destination was Ceres. New Horizon is the first ever space mission to Pluto and to the Kuiper Belt. New Horizon is the first mission to carry instruments designed, built, and flown by students. The space mission Dawn traveled 2.8 billion kilometers to get from Earth to Vesta. It will need to travel 1.6 billion more kilometers to get to Ceres. Dawn was the first spacecraft to enter orbit around an object in the main asteroid belt between Mars and Jupiter on July 16.

5 Main Dwarf Planets

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Pluto is probably the most widely known dwarf planet because it was once a planet, but reclassified as a dwarf planet. Pluto is believed to be the largest dwarf planet, but astronomers are not sure because of Pluto’s thick atmosphere. Pluto is 3.7 billion miles away from the sun and it has a surface temperature of -229ºC. It was discovered on February 18, 1930 by Clyde W. Tombaugh and was reclassified in 2006. It has five moons which are Styx, Nix, Kerberos, Hydra, and Charon which is the biggest one. Pluto’s surface is made up of nitrogen, methane, and carbon monoxide and it has polar caps. One third of Pluto is water in the form of water-ice, but this is three times as much water as there is in all of Earth’s oceans.

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One of the main dwarf planets is Ceres. Ceres was discovered in January 1, 1801, by Giuseppe Piazzi. From 1801 to the 1850's Ceres was considered a planet. It then became an asteroid and finally later became classified as a dwarf planet in 2006. Ceres is the only existing dwarf planet in our Solar System and it also happens to be the smallest. The presence of water-ice has caused conversations about life on the dwarf planet. Despite the surface temperature of -105º C the dwarf planets icy spots have started to melt and lose 6 kilograms. Ceres is too dim to see with the naked eye. The inner core consists of mostly rock and the mantle is made of water-ice.
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Eris is the most massive dwarf planet and the furthest from the sun. It has surface temperature of -231ºC and was almost named as the tenth planet. Eris is so big that all of the objects in the asteroid belt could fit into Eris! It’s only moon is Dysnomia and it was discovered on January 5, 2005 by Michael E. Brown, Chad Trujillo, and David L. Rabinowitz.

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Haumea is most different from other dwarf planets because of its shape. Haumea has an odd ellipsoid shape, which just makes the standards of the dwarf planet hydrostatic equilibrium. The reason behind the shape is simple. The dwarf planet has a very rapid rotational spin, causing it to be the least spherical dwarf planet. The shape was not caused because of the mass or weight. This dwarf planet was discovered by Michael E. Brown on December 28, 2004. In 2009, a dark red spot was found in its icy surface, which has a temperature of -241º C. Haumea is one of the densest dwarf planets. A day on Hamea is a total of 3.9 hours, which is pretty short. Lastly, Haumea has 2 main moons, named Hi'iaka and Namaka.
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Makemake is the only one of the outer four dwarf planets to not have a moon. It does not have an atmosphere, but it has a surface temperature of -239ºC. It was discovered on March 31, 2005 by Michael E. Brown, Chad Trujillo, and David L. Rabinowitz. Makemake is the only object in the Kuiper Belt that does not have a satellite.
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