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Forum » SpaceEngine » Science and Astronomy Discussions » Defining Planethood (What sets planets apart?)
Defining Planethood
WatsisnameDate: Monday, 06.06.2016, 03:20 | Message # 106
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Quote Terran ()
Under this the moon would be a planet (such a contradiction) because the sun pulls more on the moon than Earth does.


I'm not sure about this. It separates moons from planets only by the distance at which they orbit, and says nothing about the object's mass or any of its other physical or dynamical properties. Why should our Moon be a planet if it orbits at 261,000km and a moon if it orbits at 259,000km?

What if the object is in a circumbinary orbit? Do you take the vector sum of the forces from both stars?





 
steeljaw354Date: Monday, 06.06.2016, 03:20 | Message # 107
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Then everything else we can't see like Uranus,Neptune,Pluto, Eris will be dwarf planets and Ceres would be a planet and so would all other asteroids. Solar system has 10 planets we only add Eris. Not that bad? Everything else in the kuiper belt is to small to be a planet and we can discuss this in the planethood thread.

Also pluto orbiter is planned called hyper pluto orbiter http://spacenews.com/hypothe....o-pluto


Edited by steeljaw354 - Saturday, 04.06.2016, 18:42
 
spacerDate: Monday, 06.06.2016, 03:21 | Message # 108
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what about all of that?





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steeljaw354Date: Monday, 06.06.2016, 03:21 | Message # 109
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I could see maybe sedna, makemake, 2007 OR10 (new measurement) but everything else is too small.
 
HarbingerDawnDate: Monday, 06.06.2016, 03:21 | Message # 110
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Quote steeljaw354 ()
everything else is too small

Why?





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steeljaw354Date: Monday, 06.06.2016, 03:21 | Message # 111
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Or we could just use the alan stern definition. But everyone would complain at the amount of planets. (Which is the sole reason why we don't consider some objects planets because ("there are to many") https://www.youtube.com/watch?v=fvkauNOfKL4

Yes I know this includes some large moons as planets. If anything orbits a planet it is a moon. Unless it is man made.

I could re work this

1. Must be Round
2. Must not be fusing hydrogen or deuterium, then it is a star.
3. Must not orbit another object which fits this definition.
4. Must not be a black hole.


Edited by steeljaw354 - Monday, 06.06.2016, 10:36
 
SpaceEngineerDate: Monday, 06.06.2016, 03:21 | Message # 112
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Quote steeljaw354 ()
I could re work this
1. Must be Round
2. Must not be fusing hydrogen or deuterium, then it is a star.
3. Must not orbit another object which fits this definition.
4. Must not be a black hole.


I could suggest objects which fit into this definition:
- Neutron star or white dwarf.
- Young star, which does not begin fusion yet.
- Old brown dwarf, which does not fuse deuterium and lithium anymore.
- Solidified droplets of melted water/rock/iron few millimeters across.

And which does not fit:
- Two identical planets, orbiting common barycenter (binary planet) which of them is moon?
- Quickly rotating body such as Haumea (your first definition must be replaced with "hydrostatic equilibrium shape").
- Small planet after giant collision, after which it have no more "round" shape.





 
midtskogenDate: Monday, 06.06.2016, 03:21 | Message # 113
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Quote steeljaw354 ()

1. Must be Round
2. Must not be fusing hydrogen or deuterium, then it is a star.
3. Must not orbit another object which fits this definition.
4. Must not be a black hole.

I have many round objects at home, and I really hope that none of them fail criteria 2-4.





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HarbingerDawnDate: Monday, 06.06.2016, 03:22 | Message # 114
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Quote steeljaw354 ()
Which is the sole reason why we don't consider some objects planets because ("there are to many")

No, no it isn't. Stop listening to Alan Stern, he's the most insane and unreasonable authority figure in this entire debate.





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steeljaw354Date: Monday, 06.06.2016, 03:22 | Message # 115
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Proof?
 
steeljaw354Date: Monday, 06.06.2016, 03:22 | Message # 116
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1. Must have hydrostatic equilibrium
2. Must orbit a star
3. Must have a minimum radius of 1000KM
4. Must have never have been a star

Binary objects that fit this definition are planets (Pluto and Charon, Earth and Moon maybe)


Edited by steeljaw354 - Monday, 06.06.2016, 19:30
 
MosfetDate: Monday, 06.06.2016, 03:22 | Message # 117
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still off-topic I see I mean...




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Edited by Mosfet - Monday, 06.06.2016, 20:42
 
HarbingerDawnDate: Monday, 06.06.2016, 03:22 | Message # 118
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Quote steeljaw354 ()
Must have a minimum radius of 1000KM

Why?

Quote steeljaw354 ()
Proof?

I'm tempted to turn your logic about aliens back on you and say "prove that he isn't". But instead, I'll just leave you with this: https://www.theguardian.com/science....ate-row

In this article, Alan Stern claims that the demotion of Pluto was part of a decades-long conspiracy to discredit Clyde Tombaugh, a theory which is, conveniently, impossible to prove or disprove. He also claims that Mike Brown pursued the demotion of Pluto just to sell more books.

These statements are pretty unreasonable, offered with no supporting evidence, and are unbecoming a rational scientist.





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steeljaw354Date: Monday, 06.06.2016, 03:22 | Message # 119
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Well my logic of aliens and whatever is deleted now so it is irrelevant to this discussion. It is true that those statements are illogical however every scientist says unreasonable things once and a while, who are we to blame them for that? Everybody makes mistakes even you. Not everybody is perfect.

Isn't unreasonable the scientists who voted weren't actually planetary scientists and only 4% voted on a definition?

“There was an astronomer named Brian Marsden who for decades had a grudge against Tombaugh. He had public fights that many people observed. Tombaugh died in 1997 and Marsden went on a jihad to diminish his reputation by removing Pluto from the list of planets. He eventually found a way to do that at a convention of astronomers, a meeting with thousands of people, of which a very small fraction – 4% – went to a room where the vote was taken.”

"It annoys him that the science press didn’t question the process"

"you shouldn’t go to an astronomer for expert advice on planetary science."

"And it must have “cleared the neighbourhood” around its orbit, which is to say that it must be gravitationally dominant over surrounding objects. Pluto, the elliptical orbit of which is affected by Neptune’s gravity, fails this test."

“If Neptune had cleared its zone,” he has said, “Pluto wouldn’t be there.” Therefor Neptune isn't a planet by this rule.

"Stern says that if Earth was located in Pluto’s position in the solar system it also wouldn’t qualify as a planet. “It’s ridiculous,” he says. He even claims that, according to the maths, Brown’s Planet Nine would not quality for planetary status, “no matter how massive it is”.


Edited by steeljaw354 - Monday, 06.06.2016, 23:50
 
HarbingerDawnDate: Monday, 06.06.2016, 03:23 | Message # 120
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Quote steeljaw354 ()
every scientist says unreasonable things once and a while, who are we to blame them for that? Everybody makes mistakes even you. Not everybody is perfect.

It just goes to show that Alan Stern isn't some unbiased, well-reasoned expert in the field who stands a cut above the rest, which means that it is entirely unreasonable for you to keep citing him as an authority and keep citing solely his arguments, while ignoring the arguments of others in the field who are just as qualified and even more level-headed than he is.

In the rest of your quotes, you are basically just arguing that the IAU's definition of a planet is dumb. I don't think there's a single person here who would disagree with that. That does NOT mean that Stern's definition is in any way better.

You asked for evidence that Stern was unreasonable and arguably crazy. I gave it to you.





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