Is Jupiter a planet?

[Zermelo]

This is generating some interesting discussion.

In the end, I doubt that any definition can be made that negates all of the objections.  "planet" is a very ancient concept that has been tested by modern discoveries, and found wanting in some respects.  But I suspect that the professionals might have fewer problems with the terminology than some lay people.  After all, astrophysicists quite happily refer to oxygen a metal, so I'm sure planetary scientists have no hang-ups about whether an object is described as a planet, dwarf planet, asteroid, satellite, or something else.  The important thing is whether it is interesting enough to warrant study. As has been mentioned already, there are many smaller objects that have been found, unexpectedly, to be geologically active, to sport exotic lakes or glaciers, to possess subsurface oceans, to be shrouded in strange atmospheres and more.  A prime example is the lately-demoted Pluto itself, once assumed to be a boring chunk of icy rock, and now known to be one of the more interesting places in the solar system.

Edited November 28, 2023 by Zermelo

[badhex]

20 minutes ago, MalcolmP said:

Well, actually, the earth and sun combo rotate about a barycenter, but because of the mass difference that is so very near the sun center. that only a pedant would say that, so I'll get my coat >>  : )  !

Re: Jupiter ignition. When I were a lad it was said (Eddington ?) that Jupiter was just on the edge of being massive enough to become a star.
Time went on and Hoyle et al revised that to Jupiter needing to be (I think) 11 times more massive. Now it seems that figure could be anywhere in the range 13 - 90x thanks @badhex  very interesting.

I believe that the currently least massive known star is 93_MJ (Jupiter Masses) which is where that figure comes from. From 13_MJ up to 80-something_MJ it would be a Brown Dwarf which is not a true star, but very badly defined. Not sure what happens between the 80 something and 90 something though! I imagine they are giving themselves some room for error - perhaps it has been discovered that the most massive known brown dwarf is that 80 something, but I don't know. 

[badhex]

1 minute ago, Zermelo said:

This is generating some interesting discussion.

In the end, I doubt that any definition can be made that negates all of the objections.  "planet" is a very ancient concept that has been tested by modern discoveries, and found wanting in some respects.  But I suspect that the professionals might have fewer problems with the terminology than some lay people.  After all, astrophysicists quite happily refer to oxygen a metal, so I'm sure planetary scientists have no hang-ups about whether an object is described as a planet, dwarf planet, asteroid, satellite, or something else.  The important thing is whether it is interesting enough to warrant study. As has been mentioned already, there are many smaller objects that have been found, unexpectedly, to be geologically active, to sport exotic lakes or glaciers, to possess subsurface oceans, to be shrouded in strange atmospheres and more.  A prime example is the lately-demoted Pluto itself, once assumed to be a boring chunk of icy rock, and now known to be one of the more interesting places in the solar system.

Indeed! And let's not forget my fave solar system body, Enceladus, which has every possibility of harbouring life. Who needs planet status anyway if you have microbes! 😂 

[Mandy D]

@MalcolmP Although Jupiter is nowhere near massive enough to ignite hydrogen, the planet does produce it's own heat in it's core, due, I think, to gravitational effects.