4 ms·

The odd phrase "clearing the neighborhood around its orbit" exists because people want to think of Ganymede (which is bigger than Mercury) as a moon, not a plan

by dalke 10y ago

The odd phrase "clearing the neighborhood around its orbit" exists because people want to think of Ganymede (which is bigger than Mercury) as a moon, not a planet, which your proposal would do. If hypothetically we moved the Earth so it orbits Jupiter, then it would be a moon, yes? See also https://en.wikipedia.org/wiki/Clearing_the_neighbourhood#Disagreement https://en.wikipedia.org/wiki/Clearing_the_neighbourhood#Dis... .

Houshalter 10y ago
Yes I accept orbiting the sun and not another object, as a reasonable criteria of a planet. That's included in the old definition. The new definition goes well beyond that though. If there are asteroids and debris in it's orbit around the sun, it no longer counts as a planet. It's really weird, and it's only purpose is to exclude the newly discovered planets from that classification.
- dalke 10y ago
  Yes, it is weird, but I disagree with your interpretation. You wrote: "If there are asteroids and debris in it's orbit around the sun, it no longer counts as a planet." That Wikipedia link I pointed to says: "As to the extent of orbit clearing required, Jean-Luc Margot emphasises "a planet can never completely clear its orbital zone, because gravitational and radiative forces continually perturb the orbits of asteroids and comets into planet-crossing orbits" and states that the IAU did not intend the impossible standard of impeccable orbit clearing.[2] It further lists a few attempts to define things more rigorously. You write: "it's only purpose is to exclude the newly discovered planets from that classification". The same page also points out "In 2015, a proposal was made to use the criterion in extending the definition to exoplanets". This is from the same Margot, whose proposed criteria can "categorise a body based only on its own mass, its semi-major axis, and its star's mass."

by dalke 10y ago

Houshalter 10y ago

Yes I accept orbiting the sun and not another object, as a reasonable criteria of a planet. That's included in the old definition. The new definition goes well beyond that though. If there are asteroids and debris in it's orbit around the sun, it no longer counts as a planet. It's really weird, and it's only purpose is to exclude the newly discovered planets from that classification.

dalke 10y ago
Yes, it is weird, but I disagree with your interpretation. You wrote: "If there are asteroids and debris in it's orbit around the sun, it no longer counts as a planet." That Wikipedia link I pointed to says: "As to the extent of orbit clearing required, Jean-Luc Margot emphasises "a planet can never completely clear its orbital zone, because gravitational and radiative forces continually perturb the orbits of asteroids and comets into planet-crossing orbits" and states that the IAU did not intend the impossible standard of impeccable orbit clearing.[2] It further lists a few attempts to define things more rigorously. You write: "it's only purpose is to exclude the newly discovered planets from that classification". The same page also points out "In 2015, a proposal was made to use the criterion in extending the definition to exoplanets". This is from the same Margot, whose proposed criteria can "categorise a body based only on its own mass, its semi-major axis, and its star's mass."