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Pluto a Planet? New Research from UCF Suggests Yes
The reason Pluto lost its planet status is not valid, according to new research from the University of Central Florida in Orlando. 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. [...] [Philip] 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.
[...] The planetary scientist said that the literature review showed that the real division between planets and other celestial bodies, such as asteroids, occurred in the early 1950s when Gerard Kuiper published a paper that made the distinction based on how they were formed. However, even this reason is no longer considered a factor that determines if a celestial body is a planet, Metzger said.
[...] Instead, Metzger recommends classifying a planet based on if it is large enough that its gravity allows it to become spherical in shape. "And that's not just an arbitrary definition, Metzger said. "It turns out this is an important milestone in the evolution of a planetary body, because apparently when it happens, it initiates active geology in the body." Pluto, for instance, has an underground ocean, a multilayer atmosphere, organic compounds, evidence of ancient lakes and multiple moons, he said. "It's more dynamic and alive than Mars," Metzger said. "The only planet that has more complex geology is the Earth."
Planet Ceres, please.
The Reclassification of Asteroids from Planets to Non-Planets (DOI: 10.1016/j.icarus.2018.08.026) (DX)
Related: Pluto May Regain Status as Planet
Earth is a "Dwarf Planet" Because it has not Cleared its Orbit
(Score: -1, Flamebait) by Anonymous Coward on Saturday September 08 2018, @09:57AM (12 children)
ceres is not large enough. bodies have to be large so that their gravity has them become spherical in shape.
pluto is about the only thing out there that seems to fit that description that is not also a moon of something else.
that's why the debate continues.
ozcam's razor worked in the re-definition of 'base' and 'acid' as verbs (by their actions viz electrons), greatly simplifying how we think about them, and the simple spherizing notion behind the debate around pluto may win in the end as well -- its certainly used when talking about dark 'rogue planets' that are not even in orbit around anything.
(Score: 4, Informative) by takyon on Saturday September 08 2018, @10:13AM
What? [wikipedia.org]
...
https://en.wikipedia.org/wiki/List_of_possible_dwarf_planets [wikipedia.org]
https://en.wikipedia.org/wiki/Eris_(dwarf_planet) [wikipedia.org]
https://en.wikipedia.org/wiki/Makemake [wikipedia.org]
https://en.wikipedia.org/wiki/(225088)_2007_OR10 [wikipedia.org]
https://en.wikipedia.org/wiki/50000_Quaoar [wikipedia.org]
https://en.wikipedia.org/wiki/90377_Sedna [wikipedia.org]
https://en.wikipedia.org/wiki/90482_Orcus [wikipedia.org]
etc.
[SIG] 10/28/2017: Soylent Upgrade v14 [soylentnews.org]
(Score: 4, Informative) by isostatic on Saturday September 08 2018, @10:31AM (9 children)
ceres is not large enough. bodies have to be large so that their gravity has them become spherical in shape.
Ceres, and two dozen other dwarf planets and moons, are round (are in hydrostatic equilibrium)
Pluto is not the largest, it's not the roundest, it's not the best at clearing it's orbit. There's no way to come up with a measurement (no matter how arbitary) that makes Pluto a planet, but excludes something else
A major moon is round
A dwarf planet is round, and orbits the sun
A planet is round, orbits the sun, and "clears it's orbit"
There are several definitions of "clearing it's orbit", however in most Ceres does a better job than Pluto. Both Ceres and Pluto are 100 times worse at clearing their orbits than Mars
You might get away with an arbitary "planets must have radius, area, mass, and clearability in all measurements of pluto or higher. Any deficiency means it's not a planet". At least for a few more years. That's massively arbitary.
(Score: 0) by Anonymous Coward on Saturday September 08 2018, @11:51AM
Waiting for some other arbitary bodies to clear they're orbit, I guess.
(Score: 3, Interesting) by Arik on Saturday September 08 2018, @11:54AM (6 children)
"Clearing orbit" besides being problematic at other levels is a concept that rapidly loses meaning as your orbit moves away from the inner solar system and/or the plane of the ecliptic. Pluto doesn't clear it's orbit? Just how massive would a planet have to be to clear that orbit though? Is it even possible? Would Jupiter qualify as a planet, by your definition, in Plutos orbit?
If laughter is the best medicine, who are the best doctors?
(Score: 5, Interesting) by AthanasiusKircher on Saturday September 08 2018, @12:36PM
Not as rapidly as you might think. And all metrics take into account how distance from a star will influence that ability to clear the neighborhood.
Quite a bit more massive, but not anywhere near as massive as Jupiter.
Yes, by most common proposed metrics [wikipedia.org].
Yes. Look at the table toward the bottom of that Wikipedia article. By Margot's planetary discriminant (which seems to be one of the more recent and better proposed metrics, since it should be applicable to other stellar systems, not just based on parameters of our solar system, original paper available here [arxiv.org]), Jupiter would satisfy criteria for "clearing the neighborhood" in the rough lifespan of the main stellar sequence if it were even as far away as 64,000 AU. (That's roughly an entire light year from a star.) Pluto is only about 40 AU from the sun.
Pluto would have to be closer than 1.7 AU to satisfy the orbit-clearing criteria within the timeframe of the main stellar sequence. However, even Mars would be massive enough to satisfy the criteria at Pluto's distance of ~40 AU.
You can argue about the exact way these metrics are computed. But however you calculate it, there's a really big gap between the characteristics of the eight major planets vs. Pluto.
(Score: 5, Informative) by isostatic on Saturday September 08 2018, @12:38PM (4 children)
When talking hypothetical situations, I believe Margot's is the one you want. For Mars it's 54. Earth is 810, For Jupiter it's 40,000.
Pluto is 0.28.
Pluto's semimajor axis is 39.5AU.
At that distance, Earth would have a value of 13.3 and Mars 1.46
You get into the planet club with a value above 1.
So to answer your question:
Pluto doesn't clear it's orbit? Just how massive would a planet have to be to clear that orbit though?
It would be about 7.5% of Earth's mass. Mercury is 5.5%
Mars would be a planet in Pluto's orbit, but Mercury wouldn't. Pluto would be a planet if it were inside Mars's orbit, but not out as far as the Asteroid belt.
To be a planet in the inner solarsystem (as far out as Ceres), you need a mass of about 0.38% that of Earth, and pluto is 0.22%. Mercury clearly makes that.
You could argue that if a body is large enough to be able to clear it's orbit at Mars, then yes, Pluto would be allowed. But that's just arguing that a planet's mass must be at least 0.00218 times that of Earth, which is rather arbitary. But that's fine, lets accept that.
"Any body that weighs at least 10^22kg is a planet".
That would make Eris also a planet, and it's likely there will be dozens more found.
Eris would actually be a planet inside the asteroid belt, unlike Pluto, so if we're only having 9 planets, the 9th is Eris.
(Score: 1, Flamebait) by Arik on Saturday September 08 2018, @01:19PM (3 children)
It's horribly arbitrary. But it's no less arbitrary than your preferred value of 1 (it's 1 because that's what you calibrated the measure to, you could calculate it differently and make a different point 1 there's nothing magical about the number.
It seems we have two options. Choose an arbitrary value, any one is just as arbitrary as the others; or just quit trying to redefine planet in this way.
"That would make Eris also a planet, and it's likely there will be dozens more found."
It wouldn't make Eris a planet, it would fail to exclude Eris as a planet. It might still be excluded on other grounds, it's an SDO off-plane by nearly 45degrees IIRC. There are other grounds on which it might be excluded, without invoking either 'orbit clearing' or a mass requirement.
But even if it were, and there were, why would that bother you so much?
"Eris would actually be a planet inside the asteroid belt"
No, Eris is not in the asteroid belt, Eris is nowhere near the asteroid belt. You're either confusing the Oort cloud with the asteroid belt, or you're confusing Eris with Ceres.
If laughter is the best medicine, who are the best doctors?
(Score: 4, Interesting) by AthanasiusKircher on Saturday September 08 2018, @01:29PM (1 child)
You're right, there's nothing magical about any of these numbers. We're talking about SCIENCE here, not magic.
But actually, yes, there is something non-arbitrary about the number 1 here. It wasn't just chosen arbitrarily. If you actually read the original paper this metric was derived from (you notably seem to have ignored replying to my post, which dealt with the exact same issue), you'd see that the number was derived based on orbital mechanics and estimates about how a given body could clear an orbital neighborhood over the timespan of the main stellar sequence. Is that an "arbitrary" definition? Yes, in the sense that all definitions are ultimately arbitrary. But the number wasn't chosen for no reason at all, or just to exclude Pluto -- it was chosen to be meaningful both in our solar system and in other stellar systems where bodies might reasonably clear other objects around them in finite amount of time that's meaningful on the timescale of stars.
As the original article that defined that metric noted, one could choose 1/10th of the average main stellar sequence timespan as the metric, and then you'd have to increase mass by a factor of ~6. And you can tweak definitions of "orbit clearing," etc. in various ways. But they tried to come up with some reasonable standards, which had nothing to do with demoting Pluto or any other such nonsense. This is about coming up with a reasonable metric that would be useful for thinking about exoplanets, etc.
The GP wasn't confused. You are. GP in this context clearly meant inside the orbital region CLOSER TO THE SUN THAN the asteroid belt. Try reading again. And maybe try reading the original article that proposed the metric for clearing the neighborhood. You might learning something.
(Score: 1) by khallow on Sunday September 09 2018, @12:44PM
Sure, we are.
(Score: 2) by isostatic on Saturday September 08 2018, @02:57PM
No, Eris is not in the asteroid belt, Eris is nowhere near the asteroid belt. You're either confusing the Oort cloud with the asteroid belt, or you're confusing Eris with Ceres.
Neither is Pluto
The argument that "Pluto is a planet because if it were in most of the inner solar system (inside the asteroid belt) it would be a planet based on clearing orbit", is the exact same argument that "Eris is a planet because if it were in most of the inner solar system (inside the asteroid belt) it would be a planet based on clearing orbit"
(Score: 2) by requerdanos on Saturday September 08 2018, @04:25PM
Tell me about 100 times worse.
If Mars clears 100% of its orbit, say, then something 1 times worse would clear 0% of its orbit and 100 times worse would clear -9000% of its orbit... If Mars clears 88% of its orbit, then something 1 times worse would clear 0% of its orbit and something 100 times worse would clear -8712% of its orbit...
Clearly I am not understanding the concept of x times worse in a meaningful way, but you seem to understand it--would you help me to understand it?
(Score: 0) by Anonymous Coward on Saturday September 08 2018, @12:42PM
You are not even right with your chemistry. Electron behaviour defines redox reactions. Acid/base are defined by H+ donation / acceptance.