Re: "Pluto Now Called a Plutoid"

On Jun 26, 9:32 pm, Erik Max Francis <m...@xxxxxxxxxxx> wrote:
The IAU definition accomplished nothing,
except strike one of the previous members off the list.

Actually, it did accomplish something else besides that.

It kept Eris off the list.

Which was, of course, the whole point. Pluto was previously believed
to be larger and heavier than it actually was. But it was still
considerably larger and heavier than Ceres. So there was no real
urgency to decide that Pluto was, or was not, a planet as Pluto
shrank, because there was still a clear threshhold at a size smaller
than Pluto that would keep the number of planets limited.

But when the Kuiper Belt Objects started being discovered, and
especially once Eris was discovered and found to be larger than Pluto,
matters came to a head. If a new category of object existed which
would number in the hundreds, whose members would qualify as planets,
this would create a planet "gold rush", as it were, and seriously
compromise the value of the designation of a body as a planet.

Four new planets in the solar system - Ceres, Pallas, Juno, and Vesta
- was one thing. Thousands of new planets is another.

There's a big enough size gap between Mercury and Pluto that excluding
Pluto is not arbitrary, and the existence of Plutinos, showing that
Pluto's orbit is not "clear", for some value of clear that allows
Jupiter (despite its Trojans) to be a planet - and here numerical
things like Soter's Planetary Discriminant *help* give a quantifiable
justification - adds to the ability to... rationalize the decision.

But the main thing is that while it would be pleasing to add new
planets to the Solar System by ones and twos, if they bid fair to be
added by the hundreds, anything that might be so added ought to be
excluded from our definition of a planet.

However much I regret the downgrading of Pluto, after so many years of
being accepted as a planet, on an emotional level, I still understand
why it was felt to be an unavoidable decision after the discovery of
Eris.

John Savard
.

Relevant Pages

  • Re: Randome thoughts
    ... was made by Sumerians, showing the solar system with another planet, then ... Currently, the largest known dwarf planet is Eris, renamed last ... Eris is just slightly larger than Pluto, ... The moon at 1/6 the mass of the earth causes high tides. ...
    (rec.gambling.poker)
  • 10th Planet "Discovered"
    ... Object Bigger than Pluto Discovered, Called 10th Planet ... The announcement, made today by Mike Brown of Caltech, came just hours ... eluded discovery: nobody was looking there until now, ...
    (sci.space.shuttle)
  • 10th Planet "Discovered"
    ... Object Bigger than Pluto Discovered, Called 10th Planet ... The announcement, made today by Mike Brown of Caltech, came just hours ... eluded discovery: nobody was looking there until now, ...
    (sci.space.policy)
  • The Dwarf Planet Known as Eris is Bigger, More Massive than Pluto, New Data Shows
    ... The Dwarf Planet Known as Eris is Bigger, More Massive than Pluto, ...
    (sci.space.news)
  • Re: Sanity returns to astronomy
    ... Pluto no longer a planet, ... Czech Republic -- Leading astronomers declared Thursday ... "a celestial body that is in orbit around the sun, ...
    (sci.astro.amateur)