Guide to the planets…Pluto (dwarf planet)

Artist rendering of dwarf planet Pluto and its...


fact file

  • 9th planet from the sun  (distance from the sun: 3, 670, 050, 000 miles)
  • in 2006 Pluto was reclassified as a dwarf planet by the international astronomical union (IAU)
  • average surface temperature: -215 degrees C
  • 90, 553 days (248 years)
  • length of day: 153 hours, 18 minutes
  • number of moons: 5

Up until 2006 Pluto was the 9th planet from the sun, and the smallest planet in our solar system. However, in 2006, Pluto was reclassified as a dwarf planet by the International Astronomical Union (IAU). This was due to Pluto not fitting the criteria of what we call a ‘planet’.  In order for a planet to be classed as a planet, it has to be gravitationally dominant in its local neighbourhood which means it would have “cleared its neighbourhood”. Pluto however, still shares its local neighbourhood with other objects of a similar size and therefore is not gravitationally dominant, so Pluto cannot be known as a planet but rather a dwarf planet.

Pluto is around 3.7 billion miles from the sun meaning it’s surface receives very little of the sun’s heat or light, resulting in surface temperatures being as low as -230 degrees C. Pluto’s distance from the sun also means that it has a large orbit and will take the longest to complete one complete orbit of the sun. since Pluto was discovered, it is yet to complete one orbit of the sun.

Pluto has 5 moons, one of which was only recently discovered and named. Charon is the biggest of the 5 moons and is around half the size of Pluto at 737 miles in diameter. Due to both Pluto and Charon’s gravity, the two bodies are pulled into a synchronous orbit, resulting in them both facing each other with the same side all the time. Charon is coated in water ice. Nix and Hydra were both discovered in 2005 and were both thought to be formed in a collision with Pluto that also created Charon. These two moons are small and are 5,000 times fainter than Pluto. Kerberos was discovered in 2011 and was until recently only known as P4. it is Pluto’s second smallest moon with an estimated diameter of between 8 and 21 miles. Styx is Pluto’s smallest moon and was only discovered in 2012 and has until very recently been known as P5. It has a diameter of between 6 and 16 miles.