Astronomers from the Palomar Observatory in southern
California have announced the existence of a possible tenth planet in the Solar System. Its
official name is 2003 UB313. It was discovered on 21st October 2003 by Michael Brown,
Chad Trujilo and David Rabinowitz using the 1.22m Schmidt camera at Mount Palomar. It
has been given the popular name Xena.
It was named Xena informally by the discovery team and then given its current name - Eris
Eris has a period of 203 days and is about 14 500 thousand million kilometres (14.5x1012 m)
from the Sun. That puts it nearly 100 times further from the Sun than the Earth
It
lies in the Kuiper belt. This outer region of the Solar System, outside the orbit of Neptune and
extending to about 1000 AU (1000 times the distance of the Earth from the Sun), is where
short period comets are thought to originate. There are many small rocky objects in this
region but Eris is thought have a radius about the same as that of the Moon (about one and
a half times the radius of Pluto) and so is much bigger than the tiny "planetesimals"
previously discovered in this region.
The diagram shows the size of Eris's orbit
compared with those of Saturn and Pluto. The Sun is not drawn to scale nor are the sizes of
the planets themselves.
