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Eris Facts

Eris is one of five dwarf planets in our solar system. It was discovered in 2005 and presented astronomers and scientists with many questions, the hardest of which was, what is a planet? It even forced the reclassification of Pluto to a dwarf planet!

Here are some interesting facts on Eris.

  • Eris was first discovered on the 5th of January 2005. The dwarf planet was first spotted in 2003 during a Palomar observatory survey of the outer solar system. In 2005, a team who had examined photos gathered by the survey confirmed the discovery. Eris is located in the scattered disk just beyond the Kuiper belt.
  • Eris was almost considered our 10th planet in the solar system. This was mostly due to its large mass but the planet failed to meet other criteria and was labelled a dwarf planet in 2006 by the International Astronomical Union. This was when Pluto was first demoted to a dwarf planet – a decision forced by the discovery of Eris.
  • Eris was named after the Greek Goddess of discord. This name fits fairly well since it took people over a year and a half following the discovery of Eris to come to an agreement on a name. Other suggestions that were rejected included Xena, Lila and Persephone.
  • Eris is the furthest dwarf planet from the Sun. It is 9.7 billion miles (15.5 billion kilometers) away! With Ceres as the closest followed by Pluto, Haumea and Makemake. In fact Eris and its Moon are currently the most distant sighted natural objects in our entire solar system.
  • Eris has one moon. This moon is called Dysnomia – after the Greek Goddess of Lawlessness who was the daughter of Greek Goddess Eris. It is the only satellite belonging to Eris and was discovered shortly after the dwarf planet itself. It has an orbital period of 15.77 Earth days and orbits Eris in a circular pattern.
  • Eris is believed to have a rocky surface similar to Pluto’s. However due to its distance from Earth and the fact it has never been visited by a spacecraft, we will not know if this is true for quite some time.
  • Eris has a very chilly surface area of -231 degrees Celcius. This can vary a little and the atmosphere of Eris will freeze and then thaw again as its orbit brings the dwarf planet closer to the Sun and then further away again.
  • Eris takes 560.9 Earth years to orbit the Sun. As Eris was only discovered in 2005, it will be a long way outside of our life times before a full orbit of the Sun has been observed.
  • Eris is the most massive of the five dwarf planets. It has a mass 27% greater than that of Pluto.
  • Eris has a diameter of 1,451 miles (2,336 Kilometers). This is similar to the diameter of Pluto at 1,473 miles (2,370 km) so whilst Eris is definitely the most massive of the two, which one is the largest has been subject to debate. When Eris was first discovered it shone so brightly that it was assumed to be larger than Pluto. In 2010 Eris was measured through stellar occultation (this is when an object passes a star and the length of time the star is out of sight is used to calculate the size of the object) and was measured smaller than suspected.
  • So is the largest dwarf planet Eris or Pluto? The surface of Pluto refracts starlight making stellar occultation a difficult way to accurately measure its mass. Therefore its measurement of 1,473 miles has been give or take 62 miles (100 kilometers) meaning that it could be either smaller or larger than Eris. However the New Horizons Pluto flyby in 2015 has finally put an end to the speculation, reducing the margin of error in Pluto’s measurement to 12 miles (19 kilometers). Pluto is bigger! By only a few miles!

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Picture of Eris

Picture of Eris

Eris Quick Facts

Mass:16,700,000,000,000 billion kg (0.0028 x Earth)
Diameter:2,326 km (+- 12km)
Known Moons:1
Notable Moons:Dysnomia
Orbit Distance:10,120,000,000 km (68.01 AU)
Orbit Period:560.90 Earth Years
Surface Temperature:-231°C
Discovery Date:January 5th 2005
Discovered By:M.E. Brown, C.A. Trujillo & D.L. Rabinowitz

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