Pluto loses planet status
{{date|August 24, 2006}}
{{missing image|Image:Pluto Earth size comparison.jpg|thumb|Pluto's diameter is about 18% that of Earth.}}
Today, {{w|astronomy|astronomers}} have endorsed a proposal about the {{w|definition of planet|definition of the word "planet"}}. As a consequence, our solar system now counts only 8 {{w|planet|planets}}. They are {{w|Mercury (planet)|Mercury}}, {{w|Venus|Venus}}, {{w|Earth}}, {{w|Mars}}, {{w|Jupiter}}, {{w|Saturn}}, {{w|Uranus}}, and {{w|Neptune}}. {{w|Pluto|Pluto}} no longer meets the criteria and loses its planet status, but becomes the prototype of a distinct class of {{w|Dwarf planet|dwarf planets}}.

{{w|1 Ceres|Ceres}} and {{w|UB313|2003 UB<sub>313</sub>}} also have been recognised as dwarf planets. {{w|Charon (moon)|Charon}}, which was previously in the run for promotion, did not meet the final criteria for a dwarf planet.

Some 2500 astronomers from over 75 countries gathered this week in {{w|Prague}} at the Congress of the {{w|International Astronomical Union}} (IAU) to decide on several issues like a formal definition of a planet. Previously, there was no definition and with the discovery of new objects beyond Pluto there was much need for a clear criterion. The scientists also discussed new research findings in their field.

Louis Friedman, the executive director of the Planetary Society in California said: "The classification doesn't matter. Pluto — and all Solar System objects — are mysterious and exciting new worlds that need to be explored and better understood."

The final draft states: "A ''planet'' is a celestial body that 
# is in orbit around the {{w|Sun}}
# has sufficient mass for its self-{{w|gravity}} to overcome {{w|rigid body|rigid body forces}} so that it assumes a {{w|hydrostatic equilibrium}} (nearly round) shape 
# has {{w|Clearing the neighbourhood|cleared the neighbourhood}} around its orbit.

:A ''dwarf planet'' is 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 hydrostatic equilibrium (nearly round) shape,
# has not cleared the neighbourhood around its orbit, 
# is not a {{w|natural satellite|satellite}}.

:All other objects except satellites orbiting the Sun shall be referred to collectively as ''Small Solar-System Bodies''."

Pluto did not meet one of the criteria for planet: its {{w|orbit}} is highly {{w|Orbital eccentricity|eccentric}}, causing it to overlap with Neptune's. The IAU has a dozen other objects similar to Pluto on its "watchlist" and is expected to announce new dwarf planets in the coming months and years.

Ever since its discovery by American {{w|Clyde Tombaugh}} in 1930, Pluto has been considered a planet, though its status has been questioned many times after it was discovered to be far less massive than earlier calculations suggested, and because of its many other eccentricities. As a consequence of the vote, many textbooks, encyclopedias and other sources will need rewriting.

== Related news ==

*{{wikinews|title=Astronomers to vote on potential new planets|date=August 16, 2006}}

== Sources ==

*{{source-pr|url=http://www.iau2006.org/mirror/www.iau.org/iau0603/index.html
|title=IAU 2006 General Assembly: Result of the IAU Resolution votes
|pub=IAU
|date=August 24, 2006}}

*{{source|url=http://news.bbc.co.uk/1/hi/world/5282440.stm
|title=Pluto loses status as a planet 
|author=
|pub=BBC News Online
|date=August 23, 2006}}

{{publish}}
{{Archive-unreviewed}}
[[Category:Space]]
[[Category:Science and technology]]

[[Category:Czech Republic]]
[[Category:Prague]]
[[Category:Europe]]
[[Category:Astronomy]]
[[Category:Pluto]]
[[Category:Charon]]

[[ca:Plutó deixa de ser planeta]]
[[de:Pluto nur noch ein Zwergplanet]]
[[es:Plutón deja de ser considerado planeta]]
[[fr:Pluton déclassé au rang de « planète naine »]]
[[it:Gli astronomi cambiano idea: Plutone non è un pianeta]]
[[ja:冥王星を惑星から除外、国際天文学連合総会で採択]]
[[pl:Pluton zdegradowany z roli planety]]
[[pt:Plutão muda de status]]
[[ru:Плутон теряет статус планеты]]
Today, astronomers have endorsed a proposal about the definition of the word "planet". As a consequence, our solar system now counts only 8 planets. They are Mercury, Venus, Mars, Saturn, Neptune. Pluto no longer meets the criteria and loses its planet status, but becomes the prototype of a distinct class of dwarf planets.

Ceres and 2003 UB313 also have been recognised as dwarf planets. Charon, which was previously in the run for promotion, did not meet the final criteria for a dwarf planet.

Some 2500 astronomers from over 75 countries gathered this week in International Astronomical Union (IAU) to decide on several issues like a formal definition of a planet. Previously, there was no definition and with the discovery of new objects beyond Pluto there was much need for a clear criterion. The scientists also discussed new research findings in their field.

Louis Friedman, the executive director of the Planetary Society in California said: "The classification doesn't matter. Pluto — and all Solar System objects — are mysterious and exciting new worlds that need to be explored and better understood."

The final draft states: "A planet is a celestial body that 
# is in orbit around the 
# has sufficient mass for its self-rigid body|rigid body forces so that it assumes a  (nearly round) shape 
# has cleared the neighbourhood around its orbit.

:A dwarf planet is 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 hydrostatic equilibrium (nearly round) shape,
# has not cleared the neighbourhood around its orbit, 
# is not a satellite.

:All other objects except satellites orbiting the Sun shall be referred to collectively as Small Solar-System Bodies."

Pluto did not meet one of the criteria for planet: its Orbital eccentricity|eccentric, causing it to overlap with Neptune's. The IAU has a dozen other objects similar to Pluto on its "watchlist" and is expected to announce new dwarf planets in the coming months and years.

Ever since its discovery by American  in 1930, Pluto has been considered a planet, though its status has been questioned many times after it was discovered to be far less massive than earlier calculations suggested, and because of its many other eccentricities. As a consequence of the vote, many textbooks, encyclopedias and other sources will need rewriting.

*

ca:Plutó deixa de ser planeta
de:Pluto nur noch ein Zwergplanet
es:Plutón deja de ser considerado planeta
fr:Pluton déclassé au rang de « planète naine »
it:Gli astronomi cambiano idea: Plutone non è un pianeta
ja:冥王星を惑星から除外、国際天文学連合総会で採択
pl:Pluton zdegradowany z roli planety
Plutão muda de status
Space Science and technology Czech Republic Prague Europe Astronomy Pluto Charon