Re: Astronomers struggle to define 'planet'
- From: "Harvest Dancer" <harvestdancer@xxxxxxxxxxx>
- Date: 18 Aug 2006 08:44:22 -0700
http://news.aol.com/topnews/articles/_a/is-pluto-a-planet-astronomers-vote-johns/n20060818101409990005
Is Pluto a Planet? Astronomers Vote, Johns Hopkins University Takes
Straw Poll
AP
ATTENTION: Science editors
BALTIMORE, Aug. 18 (AScribe Newswire) -- Generations of schoolchildren
have memorized "My Very Energetic Mother Just Served Us Nine Pizzas"
(or a variation thereof) in order to remember the order of the nine
planets in our solar system. For 70 years - ever since it was
discovered - the "p" in that oft-repeated mnemonic device has stood for
Pluto, the ninth and smallest planet.
But is Pluto actually a planet? Or is it something else? Astronomers
have been debating this issue - often, hotly -- since Pluto's discovery
seven decades ago.
That debate may finally end next week, when members of the
International Astronomical Union meeting in Prague vote on a formal
definition of the word "planet." According to the proposed definition,
a planet is any star-orbiting object with enough mass for its own
gravitational force to pull it into the shape of a ball. Furthermore,
the object must orbit a star, without being a star itself.
If the definition is adopted, Pluto would remain and our current
nine-planet solar system would be joined by Ceres (the largest of the
asteroids), Charon (Pluto's largest moon), and 2003 UB313 (the
provisional name for a recently discovered object larger and farther
away from the sun than is Pluto). In addition, the IAU resolution also
would establish a new "junior" class of planets called "plutons" to
describe objects such as Pluto, which have less-than-circular orbits
and take more than 200 years to orbit the sun.
An informal poll of astronomers at the Henry A. Rowland Department of
Physics and Astronomy at the Johns Hopkins University's Krieger School
of Arts and Sciences and the Johns Hopkins University's Applied Physics
Laboratory reveals that though most favor Pluto's continued existence
as a planet and establishing a new definition of the word, the notion
of a "pluton" is less well-received. Here is a sampling:
Karl Glazebrook, professor in the Department of Physics and Astronomy:
"My take is that a physical definition like the one proposed makes
sense: something large enough to be spherical and which is not a
satellite. But if I were in charge, I would insist on a diameter of
greater than 1,000 kilometers to define a 'planet' in order to remove
Ceres from the list. But that would be an arbitrary cut to preserve the
order of the main nine and to save the hassle of rewriting textbooks. -
Definitions and naming really matter little physically, anyway."
William P. Blair, research professor in the Department of Physics and
Astronomy and chief of observatory operations for NASA's Far
Ultraviolet Spectroscopic Explorer Satellite, operated by JHU: "This is
really not a burning issue for most astronomers. It really is a
'classification' problem more than an issue of science. - From what I
can tell, they have tried to come up with a consistent definition: an
object roughly spherical under its own gravity, orbiting a star, and
not orbiting something else. OK, so far. Then they are apparently
willing to immediately bend this relatively simple definition and allow
Charon to itself be called a planet, with Pluto and Charon being a
'double planet' system. This goes too far and seems inconsistent to
me."
Richard Conn Henry, professor in the Department of Physics and
Astronomy: "I think the notion that Pluto is a planet is absurd. When
it was initially discovered, it was thought to be vastly more massive
than it turned out to be. Its orbit is radically different from that of
all the other planets. Down with Pluto, is what I say!"
Harold A. Weaver Jr., project scientist, Johns Hopkins University
Applied Physics Laboratory: "Personally, I'm in favor of the
resolution, mainly because it's about time we had a formal definition
of the word 'planet,' and the proposed definition is relatively
straightforward. However, we must not forget that any attempts by us to
pigeonhole objects in the universe are bound to have shortcomings. The
classification schemes that we invent help us to place diverse objects
in context, but we must also recognize that nature often doesn't adhere
to our attempts to categorize things. Although a 'planet,' Pluto has
more in common with the horde of 'Kuiper belt objects' on the outskirts
of our solar system than it does with, say, Jupiter. On the other hand,
to those who complain that Pluto doesn't deserve to be in the company
of planets like Jupiter, I point out that there are also huge
differences between Jupiter and Earth, for example. In any case, I
doubt that the IAU could come up with a resolution that would please
everyone."
Andy Cheng, Johns Hopkins University Applied Physics Laboratory: "Yes,
keeping Pluto as a planet is the correct decision. However, the new
definition of planet does not work for me, because 'hydrostatic
equilibrium' is an idealization -- it is approximately correct for
planets like Earth but is not exact. There is still no criterion for
deciding how far from hydrostatic equilibrium an object can be and
still qualify as a planet. Much of the science of geophysics deals with
the different ways, and the reasons why, planets are not quite in
hydrostatic equilibrium. Also the suggested term 'pluton' is a bad
idea, in my opinion."
CONTACT: JHU Office of News and Information -- Lisa De Nike,
443-287-9960, Lde(at)jhu.edu (After Aug. 18, Dennis O'Shea,
dro(at)jhu.edu, or Phil Sneiderman, prs(at)jhu.edu)
30- Media Contact: See above.
AScribe - The Public Interest Newswire / 510-653-9400
www.ascribe.org
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- References:
- Astronomers struggle to define 'planet'
- From: rev.goetz
- Astronomers struggle to define 'planet'
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