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A New Definition Would Add 102 Planets To Our Solar System -- Including Pluto (washingtonpost.com)
The Grim Reefer quotes a report from The Washington Post: Is Pluto a planet? It's not a question scientists ask in polite company. "It's like religion and politics," said Kirby Runyon, a planetary scientist at Johns Hopkins University. "People get worked up over it. I've gotten worked up over it." For years, astronomers, planetary scientists and other space researchers have fought about what to call the small, icy world at the edge of our solar system. Is it a planet, as scientists believed for nearly seven decades? Or must a planet be something bigger, something more dominant, as was decided by vote at the International Astronomical Union (IAU) in 2006? The issue can bring conversations to a screeching halt, or turn them into shouting matches. "Sometimes," Runyon said, "it's just easier not to bring it up." But Runyon will ignore his own advice this week when he attends the annual Lunar and Planetary Science Conference in Houston. In a giant exhibit hall crowded with his colleagues, he's attempting to reignite the debate about Pluto's status with an audacious new definition for planet -- one that includes not just Pluto, but several of its neighbors, objects in the asteroid belt, and a number of moons. By his count, 102 new planets could be added to our solar system under the new criteria. USA Today reports: "In the mind of the public, the word 'planet' carries a significance lacking in other words used to describe planetary bodies," the proposal states. "In the decade following the supposed 'demotion' of Pluto by the International Astronomical Union, many members of the public, in our experience, assume that alleged 'non-planets' cease to be interesting enough to warrant scientific exploration."
How about this?
Require hydrostatic equilibrium and that the object orbits the sun. That eliminates most asteroids and things like that. If two bodies are in hydrostatic equilibrium and the center of mass is outside of the center of either body (the Pluto-Charon system), it's a double planet. That seems logical to me. Unfortunately, the definition that's been proposed would include moons as planets, even though they clearly orbit a planet.
Nothing should be called a moon if it doesn't have the gravity to produce plasticity in the rock.
A planet is any object in orbit around a star, of sufficient mass to reach hydrostatic equilibrium, has not reached critical mass to achieve stellar fusion, and is the most prominent body in its orbit and neighborhood. That definition is going to add a few more planets but not many.
The suggested definition from TFA is just as terribly obtuse as the 2006 definition. Even worse is the suggestion to change the word 'planet' to become an all encompassing term that now also means most smaller bodies as well (but not all). It makes things unnecessarily confusing. This just seems tantamount to two-year-old logic where one word now means everything.
And look, my suggested definition expands.
A moon is any object in orbit around a planet, of sufficient mass to reach hydrostatic equilibrium, and is the most prominent body in its orbit and neighborhood.
A moonroid (haha maybe?) is any object in orbit around a planet, has not reached critical mass to achieve hydrostatic equilibrium, and is shares its orbit and neighborhood with other objects of similar mass.
An asteroid is any object in orbit around a star, has not reached critical mass to achieve hydrostatic equilibrium, and is shares its orbit and neighborhood with other objects of similar mass.
And so on. The hydrostatic equilibrium is critical to defining celestial bodies but it shouldn't be the only requirement to define a planet.
I actually really like this idea:
Define a Star as a body that has achieved a nuclear fusion reaction.
Define a Planet as a body that has enough mass to be spherical that orbits a star.
Define a Planetoid as a body that has enough mass to be spherical that does not orbit a star.
Define a Moon as a body that has enough mass to be spherical that orbits a planet.
Define an Asteroid as a body that does not have enough mass to be spherical that orbits a star.
Define a Natural Satellite (here's to you, potato shaped Phobos) as a body that does not have enough mass to be spherical that orbits a planet. Maybe call it a Moonoid?
Define Pluto and Charon as a binary planet; since they appear to orbit each other (and binary stars are already defined).
If this means Sedna and a few other bodies become planets -- fine. But at least the definitions are easy.