When astronomers found a large world farther out than Pluto, it became one of the final nails in the coffin of our ninth ...

Eris is more massive than Pluto but has a smaller volume. It has only one known Moon, called Dysnomia, and it orbits the Sun in just over 559 years. At its closest approach, Eris is 5.7 billion ...

January 5, 2005, is an astronomical anniversary that is not really marked but should be. It saw the discovery of dwarf planet Eris and how those very observations led to a new way to describe the ...