[meteorite-list] Pluto's Fate to be Decided by 'Scientific andSimple' Planet Definition

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Tue Aug 15 03:05:15 2006
Message-ID: <009201c6c039$20814750$ce29e146_at_ATARIENGINE>

Hi, All,

    Pluto has infrastructure going for it: 75 years
of textbooks and references to it as planet, down the
mnemonic they use in grade school:
    My Very Educated Mother Just Served Us Nine
Pizzas... for Mercury, Mars, Venus, Earth...

    I think the idea of the "Dwarf Planet" moniker is a mistake.
The three classes of planet proposed. Terrestrial, Gas Giant,
and Dwarf seems sensible at first, but it has flaws. Small
Rocky Worlds is a valid class. Gaseous Giants is OK (but
Neptune may be a small super-terrestrial with a whopping
big atmosphere, but why quibble...?).

    What happens to the category of "dwarf planet" when
and if we discover a TNO bigger than Mercury at 100 AU?
Or a TNO bigger than Mars at 150 AU? Why would I
think that would happen?

    Well, I've been reading everything I could get my hands on
about the planets for fifty years. When I started, the books
said that Pluto was probably 10,000 to 15,000 miles across,
then all of sudden, the newer ones reported sadly that Pluto
was only 6500 miles across, then 3700 miles, then 2500, then
maybe less than 1500, and hey! it wasn't really a planet, just an
escaped moon of Neptune, and that was the end of the solar
system, nobody home all the way out to Oortville.
    Then, Pluto got itself a moon, a big one, and it was a planet
again. But that was it -- nothing else. Then, OK, there are a
few things out there beyond Pluto, but nothing big and not
very many of those.
    Then, OK some of those things are as big as the bigger
asteroids, but they're just freaks. Heck, some of them may have
wandered in and been captured by our solar system. Basically,
the outer system is empty...
    Then, OK, there's thousands of things out there, but they're all
small, insignificant iceballs, like 25-50 km; don't worry. Well,
OK, one of these new asteroidal things out there past Pluto seems
to be bigger than Pluto and, oh, there's a few more of those
bigger things, too. And, my God! they've got moons; maybe
they're planets. And then, Pluto's got THREE moons, and one
of the newbies has got two...
    And just this month, an occultation experiment demonstrated
that the K-Belt has got lots of medium 100-200 km objects, quite
a few in fact... Well, how many? Er, about a quadrillion. (Yeah,
that's what they said, a quadrillion.) I'm not even sure how many
is a quadrillion, 10^15? It's a lot, I know that.

    Do you see a trend here, in fifty years of data?

    This is clearly detection-driven discovery. With every
improvement in our ability to detect, we find more, for 30
years now. Before you assume that you would always find
more, not so. One of the reasons for improving detection
is to reach completeness: you improve and you don't find
anything new; you finally got it all. But so far, the Outer
System just gets busier and busier.

    One of the clues is that 2003UB313 and 2005EL61 and
so forth are not that much further away than Pluto, within
10-12 AU. The detections are using parallax displacement --
watch it for three weeks and see if it moves relative to the
background sky. But objects further away move more slowly;
you have to watch them longer to detect their movement.
At this point, the searches can't afford to spend that much
time on every patch of sky, so they haven't found any bigger,
further objects... yet.

    It can't go on forever, true. No Black Dwarf star at 500 AU.
But I give it a 50-50 chance that before 2020 we will discover a
TBO bigger than Mercury or even Mars. (I hope sooner; I
hate waiting.)

    What do you do when you discover a Dwarf Planet
BIGGER than a Regular Planet? You can only spend just
so much time in committee rooms... By choosing "dwarf"
as a designation you assume facts not (yet) in evidence.

    Why not just Terrestrial, Gas Giant, and Plutonian Planets?
The 11 year old that suggested the name "Pluto" for the new
1930 Planet did so because he was the Greek god of the nether
regions, so "Plutonian" can be taken to mean "Outer System"
planets (assuming it's big enough to be round and orbits the
Sun).

    Even if Ceres gets an upgrade, it would still work, as
Ceres seems like to be "Plutonian" in composition... I have
a soft spot for Ceres.


Sterling K. Webb
-----------------------------------------------------------------
----- Original Message -----
From: "Ron Baalke" <baalke_at_zagami.jpl.nasa.gov>
To: "Meteorite Mailing List" <meteorite-list_at_meteoritecentral.com>
Sent: Monday, August 14, 2006 6:57 PM
Subject: [meteorite-list] Pluto's Fate to be Decided by 'Scientific
andSimple' Planet Definition


>
> http://space.com/scienceastronomy/060814_pluto_fate.html
>
> Pluto's Fate to be Decided by 'Scientific and Simple' Planet Definition
> By Robert Roy Britt
> space.com
> 14 August 2006
>
> A new "scientific and simple" proposal to define the word "planet" will
> be released Wednesday and astronomers will vote on it next week. It is
> not clear whether the definition will settle a long-running debate on
> the status of Pluto, however. The International Astronomical Union (IAU)
> will propose wording to delineate planets from other small objects at its
> 12-day General Assembly meeting in Prague. The meeting opened today and
> the proposal will be released to IAU member and to the public Wednesday.
>
> Committee members will not say how Pluto will be defined, but the
> diminutive planet will definitely be included in the wording.
>
> "Yes, it is very clear within what will be released - [Pluto] is very
> specifically in or out," said Richard Binzel, an MIT planetary scientist
> on a seven-person committee that developed the definition.
>
> "I think we have come up with a very reasonable definition that in the
> end will be widely adopted," Binzel said by telephone from Prague today.
> "And we will move forward. I think all will agree that it's time to move
> forward."
>
> The big mistake
>
> The roots of the problem go back to 1930, when Clyde Tombaugh discovered
> Pluto . It was classified as the 9th planet. But in recent years,
> astronomers have found other round worlds out beyond Neptune that are
> nearly as big as Pluto. One object, 2003 UB313, is the same size as
> Pluto.
>
> All these relatively small objects have offbeat orbits that trace oblong
> paths. Some, like Pluto, soar well above and below the main plane of the
> solar system in which the other eight planets orbit.
>
> For these reasons, many astronomers have long said that it was a mistake
> to call Pluto a planet, and many favor demoting it to some new class of
> object called minor planet or dwarf planet. Some think Pluto should
> remain a regular planet for cultural and historic reasons. But doing
> that would logically mean defining the handful of other small round
> worlds as planets. And experts say dozens if not hundreds more
> Pluto-like objects remain to be found on the outskirts of our solar
> system.
>
> For a year, a committee of planetary scientists within the IAU tried to
> come up with a definition. They failed. So the IAU gave the task to the
> separate 7-member panel that includes Binzel and author Dava Sobel.
>
> Owen Gingerich, an historian and astronomer emeritus at Harvard, told
> NPR last week that the proposal, "will make the Plutocrats and the
> children of the United States happy."
>
> Gingerich's words imply that Pluto will not lose planet status. One
> possibility is that the proposal would have Pluto termed a dwarf planet
> or minor planet. The setup would logically divide planets into
> terrestrial planets (Mercury, Venus, Earth, Mars), giant planets
> (Jupiter, Saturn, Uranus, Neptune) and the dwarfs.
>
> One possible alternative is Pluto could simply remain a planet with no
> prefix. This much is known:
>
> "We have come up with a surprisingly scientific definition," Binzel
> said. "It's both scientific and simple."
>
> That suggests things like size, orbital characteristics, location and
> formation method might be included in the definition.
>
> One week to ponder
>
> A vote on the definition by IAU members is slated for Thursday, Aug. 24.
> SPACE.com first reported the likelihood of this vote back in June (IAU
> members must first vote on a proposal to re-institute their right to
> vote on the matter).
>
> Most astronomers, including those very close to the issue, are in the
> dark about what will happen.
>
> "Assuming they come up with a resolution and it is presented, it is
> unclear to me if the vote will succeed," said Alan Boss, a
> planet-formation theorist at the Carnegie Institution of Washington.
> "Even if it does succeed I suspect some people will resist it."
>
> Boss was on the original IAU committee that tried to forge a definition.
> Given the inability of that group to reach consensus, and the strongly
> held opinions of various group members, Boss said trying to solve the
> problem with experts outside the planetary science community is a
> worthwhile experiment. But he's not sure it'll work.
>
> "I'd be thrilled and pleased, but I don't expect that this little
> subgroup will come up with a definition that everyone can approve and
> accept," Boss told SPACE.com today. What will really count, he said, is
> what the editors of scientific journals allow to be printed over the
> next 10 to 20 years.
>
> Everyone's favorite planet
>
> The controversy, which heated up in 1999 and has not abated since, is
> not limited to planetary scientists.
>
> "Every astronomer, not just planetary scientists, probably has a pretty
> strong opinion about how [Pluto] should be named," Boss said. "Even
> people on the street, elementary school teachers - everyone seems to have
> an opinion on this. I think it's going to be hard for people to accept
> any major changes one way or another."
>
> Boss said he wouldn't be surprised if the IAU vote will be split in
> thirds, much like the opinions of the original committee charged with
> developing a definition. And he said the vote should not necessarily be
> the end of the debate. Future discoveries of objects beyond Neptune
> could force continual re-evaluation of classification systems and
> nomenclature.
>
> "It's not necessarily something that should be decided by a vote for all
> time," he said. "Science keeps moving."
>
> Binzel is confident that resolution looms: "If we have done our job,
> this will be the end of any significant debate."
>
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Received on Tue 15 Aug 2006 03:05:01 AM PDT