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| | |-+  Pluto is no longer a planet! Poor Fwiffo!
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Author Topic: Pluto is no longer a planet! Poor Fwiffo!  (Read 12470 times)
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Re: Pluto is no longer a planet! Poor Fwiffo!
« Reply #45 on: January 13, 2007, 11:50:21 am »

That situation is not dynamically stable. They would pull on each other and eventually collide or gravitationally scatter until they weren't in the same orbit as each other.

You could do that with a Jupiter-sized planet and an Earth-sized planet, though, perhaps (there is a minimum mass ratio). What would we call that Earth, then? A trojan companion of the Jupiter. Perhaps we'd invent the term 'companion planet', which is lower in status, like 'dwarf planet', than a regular planet.

There is at least one exception, though. If those two ``planets'' are located at the opposite side of sun (they are collinear, and sun is in the middle ), have identical masses, and the shared orbit is a perfect circle.

IMHO, the ``dwarf'' implies small in size.  Otherwise when we meet Umgah, they will probably say, ``You call that big thing dwarf  planet? Good joke, better than the Maus tank!''
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Re: Pluto is no longer a planet! Poor Fwiffo!
« Reply #46 on: January 16, 2007, 01:26:03 am »

I'm not sure if pluto is going to be demoted or Ceres promoted...Too much controversy over the astronomical union's "decision" . So...

I think anything with enough gravity to form a globe and orbits the sun should be called a planet. Yes that means the asteroid Ceres that orbits between mars and jupiter.

If our solar system has thousands of these in the kuiper belt, then YES, we have thousands of planets. For clarity it could be broken down into inner (Mercury  thru Mars), middle (Jupiter thru Neptune) and Outer (Pluto, Charon and beyond)

Systems like Pluto-Charon where one planet does not clearly orbit the other and both orbit around a point in space should either be called co-planets or whichever is larger called the planet and the smaller called the moon.

This makes the most sense to me.
« Last Edit: January 16, 2007, 02:05:02 am by RTyp06 » Logged
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Re: Pluto is no longer a planet! Poor Fwiffo!
« Reply #47 on: January 23, 2007, 05:19:55 pm »

That situation is not dynamically stable. They would pull on each other and eventually collide or gravitationally scatter until they weren't in the same orbit as each other.

You could do that with a Jupiter-sized planet and an Earth-sized planet, though, perhaps (there is a minimum mass ratio). What would we call that Earth, then? A trojan companion of the Jupiter. Perhaps we'd invent the term 'companion planet', which is lower in status, like 'dwarf planet', than a regular planet.

There is at least one exception, though. If those two ``planets'' are located at the opposite side of sun (they are collinear, and sun is in the middle ), have identical masses, and the shared orbit is a perfect circle.

Though that is a stationary point of the system, it is unstable. If one of the planets were to be deflected a single angstrom inward, it would be more strongly attracted by the other planet, fall into a faster, closer orbit... by one angstrom... and then two... and four... within a few thousand years the other planet would no longer be in place. There are three such unstable points (one as you described, with equal masses; and for much lighter masses, one between us and the sun, and one further out).

There are also two stable points, sixty degrees around our orbit (one ahead, one behind). If you deflect it from those points, it sort of wanders around in circles but its deflection does not get worse.
These are what I was referring to.
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