When the Palomar Observatory detected Eris in October 2003, it was thought to be the long sought-after tenth planet in our Solar System.
Eris has a thin methane atmosphere with a rocky surface, and a small moon, Dysnomia, which orbits it every 16 days.
Eris goes round the Sun in 557 Earth years in an eccentric orbit that sometimes takes it within the orbit of Pluto.
Because Eris’s orbit takes it to 5.7 billion kilometres (3.5 billion miles) from the Sun at its closest and 14.7 billion kilometres (9.1 billion miles) at its farthest, the dwarf planet’s surface temperature is extremely cold, plummeting to as low as -243 degrees Celsius (-405 degrees Fahrenheit). The diameter of Eris is estimated at 2,326 kilometres (1,445 miles) making it about the same size as Pluto.
Originally classified as 2003 UB313, it was christened Eris in 2006 when the International Astronomical Union decided to designate it and the former planet Pluto as dwarf planets that are part of the Kuiper Belt of asteroids.
How does Eris stack up against other dwarf planets in our Solar System?
Ceres – This is the smallest dwarf planet with a diameter of just 950km (590mi). It is located in the Asteroid Belt between Mars and Jupiter and takes about 4.6 Earth years to orbit the Sun.
Pluto – The former planet has a highly inclined and eccentric orbit compared to the Solar System’s eight full-scale planets. It takes Pluto 247.7 Earth years to travel round the Sun.