Pluto has been demoted.

The tiny hunk of rock and ice at the edge of our solar system lost its status as a planet following a controversial decision by the scientific group responsible for setting the criteria for classifying objects in space.

The delegates of the International Astronomical Union (IAU) meeting in Prague for a congress voted to change the definition of what makes a planet -- a dramatic shift from only a week ago, when it looked as if the status would actually be expanded.

But instead of giving our solar system suddenly 12 planets -- since a moon and two other objects would have been upgraded -- now there are only eight. The decision ends Pluto's tenure in the celestial big leagues, where it has been since its discovery in 1930.

The IAU agreed that planets must be in orbit of a star without being a star itself. It must also have enough mass to have a round shape and have enough gravity to have cleared its orbital path of other objects. Pluto gets booted out of the planet club because its oblong orbit overlaps with Neptune's.

The new definition became necessary because as astronomers have gained the ability to peer further out into space they have been able to more precisely measure the size and features of heavenly bodies.

Pluto will now be reclassified as a "dwarf planet" and another new category "small solar system bodies" will cover even smaller objects. The celestial bodies that remain planets are Mercury, Earth, Jupiter, Saturn, Neptune, Venus, Mars and Uranus.