what are the new criteria for a celestial body to be named a planet?

Answer 1

For more information, see the official IAU site:
http://www.iau2006.org/mirror/www.iau.org/iau0603/index.html

RESOLUTION 5A
The IAU therefore resolves that "planets" and other bodies in our Solar System be defined into three distinct categories in the following way:

(1) A "planet"1 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, and (c) has cleared the neighbourhood around its orbit.

(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) shape2 , (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

(3) All other objects3 except satellites orbiting the Sun shall be referred to collectively as "Small Solar-System Bodies".


Don't forget that the new definition applies ONLY to our solar system. Not other stellar 'solar systems' at this point.

This is probably because the measurements they need to determine that status cannot be accurately made for those remote planetary systems at this time.

Answer 2

The new definition of a planet is as follows:

a celestial body that is in orbit around the sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a ... nearly round shape, and has cleared the neighborhood around its orbit.

Answer 3

Ah sure, i think you examine that Pluto has been demoted to a dwarf planet. in fact the guidelines are defined by the international Astronomical Union (IAU) placed in Prague. in accordance to them there are 3 issues that defines a planet: a.) Orbit the solar b) Are in reality around c.) Have 'cleared the community around its orbit' yet while that have been real then, purely Mercury, Venus, Saturn and Uranus could qualify because of the fact planets like Earth have a moon and asteriods interior of its orbit.

Answer 4

Planets: The eight worlds starting with Mercury and moving out to Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

Dwarf planets: Pluto and any other round object that "has not cleared the neighborhood around its orbit, and is not a satellite."

Small solar system bodies: All other objects orbiting the sun.

Answer 5

A planet must not only orbit the sun and be large enough to assume a nearly round shape, but must clear the neighborhood around its orbit.

Pluto was disqualified because it has an oblong orbit that overlaps Neptune's.