US astronomers have discovered a tenth planet orbiting Earth's sun.
The planet is the largest object found in our solar system since the discovery of Neptune in 1846.
It is the first discovery of a planet since Pluto was found in 1930.
The planet, which has been designated as 2003 UB313, measures about 3,000km in length and is a world of rock and ice.
It is more than twice as far away as Pluto, orbiting the sun just once every 560 years. It was first seen in 2003 but has only now been confirmed as a planet.
Astronomers at the California Institute of Technology, who discovered the new planet, say it went undetected for so long because its orbit is tilted at a puzzling angle.
The International Astronomical Union has verified the discovery and astronomers around the world are now turning their telescopes on the new planet.
