Neutron Star Questions: Answers to Max/Min Mass & More

[Stephanus]

They aren't planets as per the definition, but yes, they are members of the solar system. Pluto is a TNO, and it's also a dwarf planet. What differentiates a planet from a dwarf planet is whether or not it's cleared it's orbit of all other large objects. All of the planets are alone in their orbits other than their moons and some trojan asteroids, dwarf planets orbit the sun at the same distance as many other objects. There are five dwarf planets in our solar system, and six more candidates. Ceres is in the asteroid belt, the rest are at the edges of the solar system.

So, Pluto and Neptune "share" their orbit at some points, but Pluto is a dwarf planet because it's smaller then Neptune, or Pluto is a dwarf planet because it's smaller then mercury? And Ganymede is not a planet because it doesn't orbit the sun directly.

 

[newjerseyrunner]

So, Pluto and Neptune "share" their orbit at some points,

No, Neptune has it's own orbit, it's not on the same plane. Neptune has cleared out it's neighborhood. Pluto shares it's orbit with lots and lots of comets.

but Pluto is a dwarf planet because it's smaller then Neptune, or Pluto is a dwarf planet because it's smaller then mercury?

No, it's a dwarf solely because it hasn't removed all of the matter around it. If you were to replace Mars with Pluto, it would be considered a planet then.

And Ganymede is not a planet because it doesn't orbit the sun directly.

Yes, if you put it where Mars is, it would be considered a planet because it's round and there aren't asteroids in it's orbit.

Size has nothing to do with it, if you put the Earth (the biggest rocky planet) deep out in the Oorb cloud, it would be considered a dwarf planet. The size of the planet's impact on it becoming a planet or a dwarf planet is only related to whether or not that mass is sufficient to throw everything else out of orbit, or eat it itself. I'm not even sure Jupiter would be a planet if it were in the Oort cloud, I don't think enough time has passed for it to clear everything from an orbit that big.

 

[rootone]

Pluto does not share an orbit with Neptune since it's orbit is about 17 degrees tilted out of the plane which all the other planets are in (with minor discrepancies).
Also it has a much more elongated eliptical orbit.
Although at it's closest to the Sun it is somewhat closer than Neptune is, it is not at an stage in a similar orbit.

I was going to add that the size is not a consideration in the revised classification, but njr has pointed that out already.

 

[D H]

There appears to be a meme arising here: As a PF discussion grows longer, the probability of a discussion of whether Pluto is or is not a planet approaches one.

Please keep this thread on topic.