But in 2006, textbooks around the world had to be re-written, after scientists voted to reclassify Pluto as a '
dwarf planet.'
The Planets BBC2, 9pm Professor Brian Cox examines the remotest part of the solar system, a place that the most mysterious planets - Uranus, Neptune and
dwarf planet Pluto - call home.
134340 is the numeric code for the
dwarf planet given to what used to be Pluto.
Now, new evidence about the Moon's crust suggests the differences were caused by a wayward
dwarf planet colliding with the Moon in the early history of the solar system.
Our solar system's littlest was officially recognized as a planet in 1930, then downgraded to
dwarf planet status some 60 years later.
(2) A "
dwarf planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighbourhood around its orbit, and (d)is not a satellite.
The Dawn spacecraft, which was launched in 2007, does not have enough fuel to turn back towards Earth, so it will be forced to lifelessly orbit around the
dwarf planet Ceres, where it was on its last orbit before it died.
Currently, it's in orbit around the
dwarf planet Ceres, where it will remain for decades, NASA said.
Pluto was downgraded from a planet to a
dwarf planet 12 years ago.