Definition of a planet, and whether Pluto counts, is still in flux
A group will present a paper at the 48th Lunar and Planetary Science Conference in March making the case for a new definition to the word "planet."
Posted — UpdatedPrimary Investigator Alan Stern and others leading the New Horizons Mission, which studied Pluto during a 2015 fly-by, along with researchers from George Mason University in Fairfax, Va., the National Optical Astronomy Observatory in Tucson, Ariz., and the Lowell Observatory in Flagstaff, Ariz., (where Clyde Tombah discovered the once-planet in 1930) aren’t ready to give on planetary status for Pluto. The group will present a paper at the 48th Lunar and Planetary Science Conference in March making the case for a new definition to the word "planet."
The current definition, as adopted by the International Astronomical Union (IAU) in 2005 is based on three criteria:
- Is a celestial body 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 cleared the neighborhood around its orbit. (Is massive enough to have sufficient gravity to clear its path around the Sun.)
We study planets because of their physical properties, not because of where they are in space or how well they've cleared the path around sun. Planetary scientists study geologic processes both active and historic, storms brewing in the atmospheres, and they search for signs that life might have been survivable there at sometime.
With this in mind a broader definition seems appropriate. I'm not so sure about adding moons though.
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