Re: Planet Definition Revisited


"Brian Tung" <brian@xxxxxxx> wrote in message
news:ec60up$6un$1@xxxxxxxxxxxxxxxxxxx
Richard Jarnagin wrote:
Arbitrary? Not really. There is nothing arbitrary about the mass of
Pluto.
Only the choice is arbitrary, and even then, there is method to my
madness.

That's what I'm calling arbitrary. Of course I'm not saying that the
mass of Pluto itself is arbitrary; I'm not even sure what that would
mean, exactly. It is what it is.

It would serve to define an aesthetically pleasing Solar System (isn't
beauty important to all of us, subjective as it may be), and also be
useful
in classifying unseen bodies in other stellar systems as instruments
become
more advanced.

It's useful inasmuch as it's simple and precise. But it's arbitrary in
the sense that what's beautiful to you may not be beautiful to others
(many clearly prefer the cleanness of eight major planets, with all the
debris relegated to belts), and it's also arbitrary in that there does
not seem to be anything particularly special about Pluto that warrants
making its mass the dividing line.



As you seem to have noticed, all choices of a "dividing line" are arbitrary,
and indeed must be by the very nature of forming a definition. In my case,
I must admit that not only aesthetics, but history played a role in my
decision. The discovery of Pluto was too important of an event to now cast
the object aside as so much rubble. And yet, the thought of allowing every
non-satellite spherical body to now be called a planet is unsettling as
well. I also wanted a definition that could be used to classify objects in
other stellar systems as our technology progressed. Thus my choice of using
the mass of Pluto as the standard. It seems to fulfill all *my*
requirements. That others may differ goes without saying.



Mind you, I don't think it's particularly less suited to the job than
the IAU proposal. I think it's essentially impossible at this point in
time to create a definition that isn't either arbitrary or imprecise.
(Sometimes they're both.) My own definition was in response to Dale's
challenge, and an attempt to attain precision with the least amount of
arbitrariness--because I think for a definition whose stated purpose is
to be able to decide, in a timely fashion, whether something is a planet
or not, precision is more important than relevance. But at the end of
the day, I think my definition is fairly arbitrary, too. It's precise,
though--something which the IAU proposal doesn't have yet, as far as I
can tell.

Perhaps one day, when we understand the arrangement of our solar system
and that of others much better than we do now, we'll be able to answer
this question more rationally. But right now, I think we're basically
probing in the dark, both literally and figuratively.



I basically agree with everything, Brian, particularly this last paragraph.
Maybe one day...


RJ


.

Relevant Pages

  • Re: Overall disappointing...
    ... the most puzzling was the fact that Lowell had predicted that Planet X ... would have a mass 6.6 times that of Earth. ... Labeling Pluto as a Planet was a huge long-term mistake and I am glad ...
    (sci.astro.amateur)
  • Re: Strength of Materials
    ... orbit around the Sun, has sufficient mass for its self-gravity to ... "If Neptune had cleared its zone, Pluto wouldn't be there," he added. ... content to keep Pluto as a planet, and, when you discover something new ...
    (sci.physics)
  • Re: "Pluto Now Called a Plutoid"
    ... Neither of these measures is mentioned, even indirectly, in the IAU's resolution regarding Pluto or any subsequent IAU resolutions. ... "There are no other objects greater in mass than Ceres within 2 au." ... Soter's paper gives a fairly decent basis for determining whether the neighbourhood has been cleared in the concept of the planetary discriminant; the ratio between the mass of the body and the total mass of the other non-resonating and non-satellite bodies in the same orbital zone. ... The two different papers give markedly different definitions of clearing the neighbourhood but identical results, indicating that what we have done is apply the label planet to a natural class. ...
    (rec.arts.sf.science)
  • Re: Plutos a dwarf
    ... Saying that Pluto is not a planet is a lot of Mickey Mouse. ...
    (talk.origins)
  • Re: Toward a Rational Definition of what is a Planet
    ... How about we forget about trying to keep Pluto as a planet. ... significantly lower mass than at least 6 of the solar systems moons and is ... Setting the lower limit of a planet to Pluto's size would put Pluto, ... and who knows how many other objects to a higher status than many moons. ...
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