Re: "Pluto Now Called a Plutoid"

K_h wrote:

No, the context does not include oblateness; nearly round means nearly spherical. Oblate planets like Saturn are not nearly round but they are nearly spheroidal.

Something that's sphereoidal isn't round? This is silly.

All known exoplanets of main sequence stars fall well above the
gap in Figure 1 and would be classified as planets by the
criterion of dynamical dominance.

A moot point since gas giants will be discovered first. Dynamic dominance is a vague and ambiguous term and should not be used to define a planet. Imagine a solar system in formation and a growing planet that has to periodically "clear out" its neighborhood due to constantly influxing material. Under the IAU's bad definition, it is alternately a planet at sometimes and not at others. So the IAU's definition is really quite bad.

Firstly, once again I remind you that the IAU's definition doesn't currently apply to any solar system other than ours. So there's no big rush to make sure it works with edge cases like these, especially edge cases that are going to be rare and hard to detect.

Secondly, planet formation is a turbulent and dynamic time. It's planet _formation_, after all, the transition from non-planet to planet. So what's wrong with objects gaining and losing their planethood during the process? That's what it's all about.

No, see the web sites I referenced. Big dwarf planets in distant orbits is really a bad idea since "big dwarf" is a contradiction in terms.

Are you ignoring me? I gave you numbers using the method that Alan Stern himself co-developed showing that the hypothetical example you gave is as much a planet as Mars is. At this point I call straw man, you're arguing against a problem that doesn't actually exist.

Asteroids are already Minor Planets, a term which denotes an entirely
disjoint set from Planet. As the new term Dwarf Planet does.

This only underscores the need to get better definitions for things like "Minor Planets" and "Asteroids". A minor planet is not a planet? Silly. A great way to define asteroids is as objects small enough so that hydrostatic equilibrium does not apply.

Under the _original_ definition of "planet", way back when, the Moon was a planet too. Planet just meant "wanderer", an astronomical feature that's not fixed relative to the stars. So when the first asteroids were discovered there was little to distinguish them from the other planets except their relative dimness. Scientific definitions evolve over time as our understanding of the subject grows.

We can wait having more information about what there is to classify
before classifying them, in other words we should wait and see what is
out there before deciding how to classify them.

Bad idea. It means constantly updating the definitions as new information comes along. The example definitions I provided do not require constant reclassification as new data arrives.

You realize that measuring exoplanetary diameters is generally harder to do with precision compared to mass and orbital period? As far as I'm aware unless you're lucky enough to have the exoplanet's orbit line up in such a way that it transits across the face of its primary there's no way to even try.

This is a bad way to define a planet. Try defining a building in such a way that it is only a building unless it dominates its surroundings.

Why? I don't see any connection between the two.

"Seems?" Definitions should not be justified by how things "seem". The example I gave, with a star, a brown dwarf, and two jupiter type planets at L4 and L5 clearly show that the "clearing its orbit of debris" is a very bad way to define an word like "planet".

A hypothetical case with no indication that it's particularly likely to occur. And if it does, so what if the two trojan objects aren't defined as planets? They're behaving quite differently from all the other known planets. They might even warrant a class of their own.

Generally, objects are defined by the properties intrinsic to themselves, not what is or is not in their neighborhoods.

How do you define something as a "moon" if not in relation to what's in its neighborhood? It's perfectly cromulent to define something based on the context it's embedded in, among other characteristics. Lots of things are defined that way.
.

Relevant Pages

  • Re: Likeliness of Pluto discovery
    ... And if that means classifying other objects in the solar ... Quaoar is already classified as a planet. ... is the dividing line between major and minor planet. ...
    (sci.astro)
  • Re: Likeliness of Pluto discovery
    ... The way I see it, if it's round and orbits the Sun, it's a ... And if that means classifying other objects in the solar ...
    (sci.astro)
  • Nepurcele, they are watching you from Lagrangian L$ & L5
    ... Earth's orbit, one marching ahead of our planet, the other trailing ... Astronomers call them Lagrangian points, ... of naming these asteroids after characters from the Trojan wars. ... the twin STEREO probes was placed ahead of Earth, ...
    (soc.culture.romanian)
  • Re: ONeill habitat spin axis
    ... Putting it in orbit around a planet or near a planet might ... This method is easier rather than moving asteroids into prefered orbit ... > I'd ideally like to point it at the sun. ... believe that it might be a ancient space colony. ...
    (sci.space.tech)
  • Re: "Pluto Now Called a Plutoid"
    ... hydrostatic equilibrium and is nearly round. ... general, parentheticals are for clarification only, and the greater ... about "hydrostatic equilibrium", and not a further restriction of it. ... The people who wrote the definition consider Saturn to be a planet. ...
    (rec.arts.sf.science)