Xena | Universe Today

Written by Jerry Coffey

Xena was the informal name given to the dwarf planet Eris by the team that discovered it. Eris is 27% more massive than Pluto, so the team originally thought that they had discovered the 10th planet or Planet X. The television show Xena was popular at the time and the group felt that the name was a sound one for their new planet.

Xena now has the formal designation of 136199 Eris. It is the largest known dwarf planet in the solar system and the ninth-largest body known to orbit the Sun. It is approximately 2,500 kms in diameter and 27% more massive than Pluto. The dwarf planet was discovered by a team led by Mike Brown which included Chad Trujillo, and David Rabinowitz while using the Palomar Observatory. It is a trans-Neptunian object (TNO) native to the scattered disc. Eris is known to have one moon, Dysnomia. The dwarf's distance from the Sun is roughly three times that of Pluto, 96.7 astronomical units(AU) and has an orbital period of 557 years. Other than a few comets the pair are the most distant known natural objects in the Solar System. The discovery of Eris was long overdue. It was eventually found in images that were two years old. The discovery team had to reanalyze their images and look for objects moving at much slower speeds than they were looking for at first.

There was some difficulty classifying Eris at first; hence the name Xena being applied to it in the beginning. It eventually led to the International Astronomical Union(IAU) clearly defining a planet and the loss of planethood by Pluto. The IAU did this in their paper Definition Of A Planet In The Solar System that was adopted on August 24, 2006. By that definition Eris is a dwarf planet and TNO; the intersection of these categories is a plutoid. Eris' orbital characteristics can be used to more specifically categorize it a scattered disc object (SDO), or a TNO that is believed to have been "scattered" from the Kuiper belt into more distant and unusual orbits because of gravitational interactions with Neptune in the early solar system formation. Its high orbital inclination is unusual among the known SDOs, but some theoretical models suggest that objects that were originally near the inner edge of the Kuiper belt were scattered into orbits with higher inclinations than objects from the outer belt. Inner-belt objects are expected to be generally more massive than outer-belt objects, and so astronomers expect to discover more large objects like Eris in high-inclination orbits, which have traditionally been neglected.

Eris or Xena, whichever you prefer to call it, was among a set of TNOs that were discovered all at once and set the astronomy world on its ear for a short time. There is a good article about Eris here. Here on Universe Today we have a great article about the renaming of Xena and another about its moon. Astronomy Cast offers a good episode about Pluto's loss of planethood which includes the three requirements of being called a planet.

Filed under: Astronomy