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Scientists against the demotion of objects like Pluto, Eris, Sedna, etc. to "dwarf planet" status have crafted a new definition:
It's no secret that Alan Stern and other scientists who led the New Horizons mission were extremely displeased by Pluto's demotion from planet status in 2006 during a general assembly of the International Astronomical Union. They felt the IAU decision undermined the scientific and public value of their dramatic flyby mission to the former ninth planet of the Solar System.
But now the positively peeved Pluto people have a plan. Stern and several colleagues have proposed a new definition for planethood. In technical terms, the proposal redefines planethood by saying, "A planet is a sub-stellar mass body that has never undergone nuclear fusion and that has sufficient self-gravitation to assume a spheroidal shape adequately described by a triaxial ellipsoid regardless of its orbital parameters." More simply, the definition can be stated as, "round objects in space that are smaller than stars."
From the proposal:
The eight planets recognized by the IAU are often modified by the adjectives "terrestrial," "giant," and "ice giant," yet no one would state that a giant planet is not a planet. Yet, the IAU does not consider dwarf planets to be planets. We eschew this inconsistency. Thus, dwarf planets and moon planets such as Ceres, Pluto, Charon, and Earth's Moon are "fullfledged" planets. This seems especially true in light of these planets' complex geology and geophysics. While the degree of internal differentiation of a given world is geologically interesting, we do not use it as a criterion for planethood in the spirit of having an expansive rather than a narrow definition.
Here's another article about the significance of the New Horizons mission. New Horizons will fly by 2014 MU69 on January 1, 2019.
(Score: 1, Insightful) by Anonymous Coward on Wednesday February 22 2017, @01:57PM
Historically, the planets were those that were visible to the naked eye. The moon was in a category of its own.
These are large bodies that orbited the sun. We found other bodies later orbiting the sun and added them. Problem is we found SO MANY bodies orbiting the sun... you have to limit them or it ceases to be a useful term. I could go either way on Pluto, mostly because it traditionally was accepted as a planet, but I wouldn't add any more. In the end, it's purely a status thing for Pluto scientists--nothing more.
(Score: 2) by TheRaven on Wednesday February 22 2017, @02:03PM
sudo mod me up
(Score: 2) by VLM on Wednesday February 22 2017, @02:45PM
Of course when I was a kid there were nine planets. I don't predate Pluto. Now there are thousands of exoplanets, so we don't expect kids to memorize all 2000 or so known exoplanets. Most don't even have names and more are discovered every week.
I'd compare it to constellations. We kinda expect kids to learn the constellations in their hemisphere... kinda... sorta, well at least we'd like to even if the kids don't learn or forget five minutes later. And that constellation list is a large number. So as long as we keep the number of planets to less than a hemisphere's worth of constellations we're not being too unreasonable.
One way to describe a planet under these criteria is "here's something big enough to someday be economically useful". If there's "too many", well, "too bad".
(Score: 3, Insightful) by khallow on Wednesday February 22 2017, @04:19PM
You end up with the solar system being Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Ceres, Pluto, Haumea, Makemake, and Eris now, which isn't too bad, but there are an estimated 200 objects with similar characteristics to Pluto, and no one is going to remember that list.
Why is that supposed to matter? The real problem here is that the current definition only works for the Solar System. In other star systems, you may have either lack of information to determine the "clearing of orbit" of a body or weird orbital dynamics that prevents us from even defining "clearing the orbit" (such as in a binary star system where multiple large exoplanets have the same resonance dynamics with respect to the smaller star as Pluto and the other current trans-Neptunian dwarf planets have with respect to Neptune, alternately hang out in the L4/L5 positions of the binary system, or orbiting inside a ring of material like Saturn's "shepherd moons").
It's hard to determine orbital dynamics and what other bodies may be precluding the potential planet from being a planet, but fairly easy to determine mass.
(Score: 1) by toddestan on Sunday February 26 2017, @06:45AM
And if that's what happens, what is the problem with there being some many planets? Used to be that Jupiter had 4 moons. Now it has dozens of moons, some of which I'm pretty sure don't even have proper names. Yet I don't see everyone redefining what a moon is just because no one can remember all of Jupiter's moons.
(Score: 4, Insightful) by jdavidb on Wednesday February 22 2017, @02:04PM
ⓋⒶ☮✝🕊 Secession is the right of all sentient beings
(Score: 0) by Anonymous Coward on Wednesday February 22 2017, @02:44PM
I don't know why this was modded "Touche".
It doesn't contradict my point about the definition being somewhat arbitrary and historical, starting as those objects that were visible (and BTW, that moved, unlike the stars). Certainly the moon (and the sun) are considered differently because they are so close to us.
The point is that there -is- no objective criteria for what is a "planet." We tend to redefine it time to time so it just so happens to include all the historical planets as a requirement.
(Score: 0) by Anonymous Coward on Wednesday February 22 2017, @02:49PM
To clarify, I meant the historical planets to be those we considered planets in the 1700's and 1800's when the generally agreed definition was basically a large body that orbited the sun.
(Score: 0) by Anonymous Coward on Wednesday February 22 2017, @02:52PM
Also to clarify, the sun and moon might be considered planets in ancient times, but I meant "considered differently" in a *qualitative* sense.
The sun lights up the sky and gives life and days, the moon has phases and gives tides, etc.
(Score: 2) by bzipitidoo on Wednesday February 22 2017, @03:35PM
"Planetes" means "wanderer". "Planetes asteres", planets for short, are stars that do not stay fixed relative to other stars. but which wander across the sky. While the sun and the moon both "wander", those are in categories of their own. Note also the original definition fails to include Earth itself.
(Score: 2) by jdavidb on Wednesday February 22 2017, @03:17PM
I was shooting for "informative" or "interesting" or something.
If I understand correctly the original word for planet basically meant "traveler" and meant the celestial objects that move to different locations in the sky each night as opposed to the stars which move but much more slowly. I remember at some point being surprised to learn that also included the moon and sun, although I'm not sure if every culture classified them that way.
ⓋⒶ☮✝🕊 Secession is the right of all sentient beings
(Score: 2) by takyon on Wednesday February 22 2017, @02:37PM
The discovery of Pluto so early in the 20th century was supposedly an accident (due to inaccurate calculations of mass of Neptune, they were looking for something that effected the orbits of Neptune and Uranus), and the naming of a Disney character after the planet helped to make it iconic. It wasn't clear until 1976-1978 that its mass was so small (the albedo was calculated, and then Charon was discovered). Further TNOs weren't found until 1992. Now we are finding largish dwarf planets [wikipedia.org] faster than we can dish out the names.
On the other hand, Pluto has the largest volume of any of the TNOs we have found, although Eris came close to dethroning it (and still might if we get better measurements of it). Pluto's relatively large size compared to similarly-orbiting objects like Ixion and Huya probably helped it get discovered so early.
Dwarf planet is a good enough status for Pluto, in my opinion. Unless you want to let in Ixion, Huya, Salacia, Orcus, Haumea, Makemake, Eris, Sedna, Varuna, Quaoar, Etcetera, and all the unknown tiny ice objects that are rounded and have elongated orbits. Planet Nine offers the best chance to shake things up. There's also talk of Mars-sized TNOs. Neptune determines the orbits of Pluto and plutinos, but it doesn't look like that will be the case for Planet Nine and possibly other TNOs. Now that would be something, getting Planet Nine added to the list of planets along with a couple of 4,000+ km diameter TNOs.
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(Score: 0) by Anonymous Coward on Wednesday February 22 2017, @03:10PM
It wasn't named after a disney character
The name Pluto, after the god of the underworld, was proposed by Venetia Burney (1918–2009), a then eleven-year-old schoolgirl in Oxford, England, who was interested in classical mythology.[35]
Pluto debuted in 1930, the same year as pluto the planet was discovered. Do you really think they named a planet after a brand new cartoon character?
(Score: 2) by takyon on Wednesday February 22 2017, @03:28PM
Read carefully, bruh:
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(Score: 0) by Anonymous Coward on Wednesday February 22 2017, @05:42PM
I misread it then, although the sentence could have been cleared up some with better wording. Apologies.
(Score: 2) by takyon on Wednesday February 22 2017, @09:39PM
Fair enough. I was not caffeinated.
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(Score: 2) by FatPhil on Wednesday February 22 2017, @11:07PM
Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves
(Score: 5, Insightful) by theluggage on Wednesday February 22 2017, @02:59PM
Problem is we found SO MANY bodies orbiting the sun... you have to limit them or it ceases to be a useful term.
Why? Or rather, why does it cease to be a useful term? "Planet" already covers everything from Mercury to Jupiter (even before dragging exoplanets into the argument) so its not scientifically useful without further sub-categories (and it would be ridiculous to have a different set of sub-categories for moons and exoplanets that shared the same planetographical features).
Whether or not Pluto "is" a planet is non-falsifiable - planet is an arbitrary definition that has already changed several times. The problem with the IAU decision is not that it is "right" or "wrong" but that the whole "must clear your orbit (but only if your name begins with 'P') " thing appears to be a contrivance purely intended to eliminate Pluto. The justification that "we'd have to accept 100 other bodies as planets" is just as much a weak "appeal to tradition" as "but we all learned that Pluto was a planet...".
If you can't cope with 100 solar planets + a zillion exoplanets, here's my two proposed alternate definitions of "Planet":
"Planet (1)": One of Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto and "Hypothetical Planet 10/X/Rupert" if it shows up, because we've been calling them bloody planets for years, that's what the textbooks say and there's no scientifically valid way of deciding otherwise. Or:
"Planet (2)": One of Mercury, Venus, Earth, Mars, Jupiter, Saturn or Uranus (and maybe some of the bigger asteroids). I.e. the planets that were initially identified by observation because they moved against the background of "fixed" stars which was what "planet" originally meant. Sorry, Neptune, Pluto, Rupert - you were only observed after being predicted from the perturbations in the orbits of real planets.
(Score: 2) by tangomargarine on Wednesday February 22 2017, @03:57PM
"Planet" already covers everything from Mercury to Jupiter
asteroid belt
"Is that really true?" "I just spent the last hour telling you to think for yourself! Didn't you hear anything I said?"
(Score: 2) by theluggage on Wednesday February 22 2017, @04:44PM
asteroid belt
Sorry - ambiguous - I meant "the range of planet types from Mercury to Jupiter".
(Score: 2) by tangomargarine on Wednesday February 22 2017, @05:07PM
'planet' already covers everything that's already a planet
Department of Redundancy Department
If what you mean is "there are no dwarf planets from the Sun out to Jupiter"...
Ceres (/ˈsɪəriːz/;[18] minor-planet designation: 1 Ceres) is the largest object in the asteroid belt that lies between the orbits of Mars and Jupiter. Its diameter is approximately 945 kilometers (587 miles),[6] making it the largest of the minor planets within the orbit of Neptune. The 33rd-largest known body in the Solar System, it is the only dwarf planet within the orbit of Neptune.[c][19]
"Is that really true?" "I just spent the last hour telling you to think for yourself! Didn't you hear anything I said?"
(Score: 2) by maxwell demon on Wednesday February 22 2017, @09:12PM
If you engage your brain, it's fairly obvious what was meant: The term "planet" already covers objects of such a wide range of different properties ranging from Mercury (a relatively small rock ball) to Jupiter (a gigantic gas ball).
The Tao of math: The numbers you can count are not the real numbers.
(Score: 2) by tangomargarine on Thursday February 23 2017, @03:44PM
I did engage my brain. The point they were making was totally wrong.
"Is that really true?" "I just spent the last hour telling you to think for yourself! Didn't you hear anything I said?"
(Score: 2) by theluggage on Thursday February 23 2017, @05:02PM
I'll try again: The term "Planet" already covers a range of bodies as diverse as gas giants (Jupiter) and small, rocky worlds (Mercury) so its never going to be sufficient as a term for classifying objects. That clear enough?
(Score: 2) by tangomargarine on Thursday February 23 2017, @05:53PM
Crystal. Thanks.
"Is that really true?" "I just spent the last hour telling you to think for yourself! Didn't you hear anything I said?"
(Score: 2) by FatPhil on Wednesday February 22 2017, @11:13PM
It's true you could have worded it in a more spoon-feedy manner, but it was clear enough what you meant, IMHO, as you couldn't have meant the above, and therfore some other range was being expressed by your "from .. to ..".
Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves
(Score: 2) by tangomargarine on Thursday February 23 2017, @03:47PM
Oh, range of *properties*? I was reading that as "geographical range," and past Jupiter was excluded because it was common knowledge dwarf planets were in that area.
Guess my eyes skated over "types" for some reason :P
"Is that really true?" "I just spent the last hour telling you to think for yourself! Didn't you hear anything I said?"
(Score: 2) by Arik on Wednesday February 22 2017, @06:25PM
If laughter is the best medicine, who are the best doctors?