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Little Pluto, formerly the solar system's smallest planet, has been stripped of its status by the Internatiuonal Astronomical Union, reducing the number of planets to eight.
The new guidelines − introduced in Prague on Thursday after a week of debate by the 2,500 astrometers at the organization's conference − define what is a planet and what is not.
Pluto didn't make the cut.
Pluto has been considered a planet since its discovery in 1930.
Under the new guidelines, it's now considered a "dwarf planet," leaving eight planet −Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
Pluto, which is smaller than Earth's moon, doesn't fit the new criteria for a planet: "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."
Pluto doesm't qualify because its orbit is inclined relative to the rest of the solar system and crosses over the orbit of Neptune.
NASA said Thursday that Pluto's designation as a dwarf planet would not affect its $700-million US NEW Horizons spacecraft mission,
launched earlier this year.
The spacecraft will reach Pluto after a 9 1/2-year journey.
THe IAU also introduced a third class, "small solar-system bodies,"
for objects smaller than dwarf planets, such as asteroids and comets, that orbit the sun.
Astronomers have been working without a solid definition of a planet since the dats of Corpernicus.
The new definition fill that void.
Just a week ago, the IAU's leader suggested a different definition for a planet that would have included Pluto, its moon Charon,
the asteroid Ceres and a recently discovered object, 2003 UB313, which is slightly larger than Pluto and was nicknamed Xena.
The new guidelines − introduced in Prague on Thursday after a week of debate by the 2,500 astrometers at the organization's conference − define what is a planet and what is not.
Pluto didn't make the cut.
Pluto has been considered a planet since its discovery in 1930.
Under the new guidelines, it's now considered a "dwarf planet," leaving eight planet −Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
Pluto, which is smaller than Earth's moon, doesn't fit the new criteria for a planet: "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."
Pluto doesm't qualify because its orbit is inclined relative to the rest of the solar system and crosses over the orbit of Neptune.
NASA said Thursday that Pluto's designation as a dwarf planet would not affect its $700-million US NEW Horizons spacecraft mission,
launched earlier this year.
The spacecraft will reach Pluto after a 9 1/2-year journey.
THe IAU also introduced a third class, "small solar-system bodies,"
for objects smaller than dwarf planets, such as asteroids and comets, that orbit the sun.
Astronomers have been working without a solid definition of a planet since the dats of Corpernicus.
The new definition fill that void.
Just a week ago, the IAU's leader suggested a different definition for a planet that would have included Pluto, its moon Charon,
the asteroid Ceres and a recently discovered object, 2003 UB313, which is slightly larger than Pluto and was nicknamed Xena.
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