Slashdot Mirror
Pluto Should Be Reclassified as a Planet, Experts Say (sciencedaily.com)
The reason Pluto lost its planet status is not valid, according to new research from the University of Central Florida in Orlando. From a report: In 2006, the International Astronomical Union, a global group of astronomy experts, established a definition of a planet that required it to "clear" its orbit, or in other words, be the largest gravitational force in its orbit. Since Neptune's gravity influences its neighboring planet Pluto, and Pluto shares its orbit with frozen gases and objects in the Kuiper belt, that meant Pluto was out of planet status. However, in a new study published online Wednesday in the journal Icarus, UCF planetary scientist Philip Metzger, who is with the university's Florida Space Institute, reported that this standard for classifying planets is not supported in the research literature. Metzger, who is lead author on the study, reviewed scientific literature from the past 200 years and found only one publication -- from 1802 -- that used the clearing-orbit requirement to classify planets, and it was based on since-disproven reasoning. He said moons such as Saturn's Titan and Jupiter's Europa have been routinely called planets by planetary scientists since the time of Galileo.
"The IAU definition would say that the fundamental object of planetary science, the planet, is supposed to be a defined on the basis of a concept that nobody uses in their research," Metzger said. "And it would leave out the second-most complex, interesting planet in our solar system." "We now have a list of well over 100 recent examples of planetary scientists using the word planet in a way that violates the IAU definition, but they are doing it because it's functionally useful," he said. "It's a sloppy definition," Metzger said of the IAU's definition. "They didn't say what they meant by clearing their orbit. If you take that literally, then there are no planets, because no planet clears its orbit."
"The IAU definition would say that the fundamental object of planetary science, the planet, is supposed to be a defined on the basis of a concept that nobody uses in their research," Metzger said. "And it would leave out the second-most complex, interesting planet in our solar system." "We now have a list of well over 100 recent examples of planetary scientists using the word planet in a way that violates the IAU definition, but they are doing it because it's functionally useful," he said. "It's a sloppy definition," Metzger said of the IAU's definition. "They didn't say what they meant by clearing their orbit. If you take that literally, then there are no planets, because no planet clears its orbit."
Jerry Smith.
The redefinition of the phrase presented in the summary is silly. “Clearing its orbit” means just what it says. But then Neptune also fails that test, since it hasn’t “cleared its orbit” of Pluto - and therein lies the problem.
If scientists had meant a planet should “be the largest gravitational force in its orbit”, they would have said exactly that. The phrasing is clear, concise, and unambiguous.
#DeleteChrome
We don't consider medical definitions in the context of the four humours, heck late 19th century astronomers thought space was filled with luminiferous aether so why are their opinions on the definition of planets suddenly considered insightful.
So how many planets do you want?
If we let Pluto be a planet, then our solar system will also have to start officially calling all the other minor planets, planets. i don't think that's reasonable or important. its simply not worth it. Pluto is a an object, we know its there, but it doesn't need to be on a list that includes the 8 major planets. i don't care how you categorize it, we simply cannot have a never ending list of planets to include in our definition of the solar system.
-Jeff
Read the Wikipedia article on clearing the neighborhood. It's defined well enough and people know what it means. Claiming that "If you take that literally, then there are no planets, because no planet clears its orbit." is like pointing to the requirement that a planet must be round, and saying that if you take that literally, no planet is round. Yes, no planet is 100% round, but it's possible for a planet to be close to round or not very close to round, and the same goes for clearing the neighborhood.
The research that shows that nobody used this definition in the past is probably correct. But it doesn't help. Scientists can make up new definitions.
Furthermore, while it's also true that planetary scientists call lots of things planets, the report itself admits that they also use the term for moons. Nobody else is going to start calling Pluto a planet under a definition that also includes moons.
Additionally, its mass should be enough to form a spheroid. Pluto looks like a goddam potato.
You may want to check that again before you say it around anyone in person. Pluto is nicely spherical. Perhaps you're thinking of Vesta?
If Pluto identifies as a planet then I think we should respect that decision. Maybe Pluto is astronomical body fluid, one day a planet, the next day not.
Its not about emotions, it's about useful terminology. To a planetary scientist, a planet is a body that's large enough to be in hydrostatic equilibrium, which creates a fundamental distinction between two very different types of bodies. A body in equilibrium is differentiated, has been altered by fluids, has experienced geothermal heat over long time periods, etc. A body not in equlibrium is undifferentiated and - if old - comprised of the primitive relics of our solar system. To a planetary scientist, the large moons are likewise "planetary" moons, in that they're gone through the same sort of differentiating processes as planets; their position and path of motion does not change what they are.
The IAU, which is primarily astronomers and not planetary scientists, made a big mess for actual planetary scientists. Rather than creating their own new orbital classification for their needs, they took away a term in widespread use from another set of scientists. The latter have been the leading voices for overturning the IAU decision since then.
The fact that the planetary science definition is much closer to the popular definition than the IAU definition is is actually a side point. Although one worth bringing up nonetheless. New Horizons lead Alan Stern likes to bring up the "Captain Kirk Test", when discussing the popular usage of the term, as distinct from either scientific usage of the term. That is, if the Starship Enterprise was in orbit around it, and Captain Kirk said "Beam us down to that (blank)", would that word be "planet", or something else? As humans, we automatically recognize "object in space so large that its gravity has pulled it into a sphere" as a planet. To the point that we sometimes struggle when discussing science fiction when such bodies are presented as moons. Think of how many times you've heard Star Wars fans refer to the Forest Moon of Endor as a planet or whatnot.
Of course, all *this* is tangential to the fact that the IAU definition is a completely self contradictory minefield based on false premises (foremost of which is that planets actually clear their own neighborhoods - Mars's neighborhood, for example, was primarily cleaned by Jupiter, not Mars***), but that's an entirely different story....
*** No, the Stern-Levison parameter doesn't help. It's based on a current body's ability to clear asteroids, not a planetisimal's ability to clear other planetisimals. And indeed, Stern is as mentioned one of the biggest opponents of the IAU definition. Basing your argument on a guy who disagrees with it is never a good start!
They carry weapons and they know if you've been bad or good. Not everybody's good, but everyone tries.
I saw research being described. A metastudy is considered research.
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
It makes a huge difference. Basically, if you can't classify Pluto then there's no point in bothering with astronomy or planetary science since you can't predict or classify. In fact, you might as well jump off a building since it renders science and modern life futile if you cannot predict or classify. You're left only with religion.
One, and only one, designation will be useful in any predictive or functional sense. To use any other designation is the work of mystics, not planetary scientists.
What that designation is can be determined only by looking at what has actual scientific value, not what has votes in a conference.
Understood? Good.
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
No. The eggheads didn't attend the IAU conference. Most aren't even astronomers.
This hasn't been settled because nobody agrees on the basis. The IAU doesn't want school textbooks with 22 planets in the solar system, the some reason for reclassifying. Planetary scientists don't give a crap about the books and want a definition with actual meaning.
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
Any definition of planet has to be true for:
All objects universally agreed on in our solar system to be planets
All exoplanets of Earth size or larger
All rogue planets that are not brown dwarfs
All planets within accretion disks
This basically means you can't use shape, orbit or objects in proximity in your definition.
Your definition must exclude all:
Rocky asteroids
Rubble pile asteroids
Comets
Brown dwarves
Stars
Dead stars in orbit around other stars
That's not going to be easy, since a lot of characteristics are shared.
Finally, any definition must be as simple as possible and predictive. On seeing a new planetary object, given a certain perfect subset of characteristics plus the definition, we must be able to infer at least one other thing about the object. Otherwise, it's not a useful definition.
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)