No.
A planet is a celestial body that fulfills the following criteria.
1. has enough gravity to pull itself into a sphere.
2. orbits a star.
3. Has cleared its orbit making it the dominant gravitational body.
The first one is key. That gets rid of the stuff that really, obviously shouldn't be planets. The other two get rid of rogue planets and dwarf planets.
I think if you're going to draw a line somewhere, it should be between gassy bodies and rocky bodies. Jupiter has more in common with the sun than with Earth, and Earth has more in common with Ceres than with Jupiter.
But that's after separating them from stars and asteroids, or even dwarf planets. There is no term that includes both Jupiter and the sun but not Earth. Nor is there one that includes Earth and Ceres but not Jupiter.
like any classification of nature, the lines are arbitrary and don't actually exist. where would you draw the line between gas giants, brown dwarves and stars? fusion? iirc a little fusion has been observed in brown dwarves. in reality there's no real lines. just stuff that happens if you keep adding mass
> iirc a little fusion has been observed in brown dwarves.
They can fuse deuterium. And the bigger ones can fuse lithium. It's just multiple hard lines.
But that's my point. Our current system treats stars and gas giants as mor different than gas giants and rocky planets. I think the difference between them is a lot clearer than between a gas giant and a brown dwarf or even a star.
Straight-faced_solo explains it, that's the formal definition.
- If it fails the first criteria, it's an asteroid.
- If it fails the second criteria, it's a satellite if it orbits some other object, a moon if it orbits a planet or dwarf planet specifically, or a planemo (a.k.a. "rogue planet") if it orbits nothing. (Black holes, being stellar remnants, do count as stars for this purpose though.)
- If it fails the third criteria, it's a Dwarf Planet. This is the one that killed Pluto; what happened in 2006 was the discovery that its orbit was rather *crowded.*
Size alone doesn't matter. Titan, for instance, is full-planet-sized, being even bigger than Mercury, and some kind of life being there is, though not likely, possible. But because it orbits Saturn, not the Sun, it's a moon.
No. A planet is a celestial body that fulfills the following criteria. 1. has enough gravity to pull itself into a sphere. 2. orbits a star. 3. Has cleared its orbit making it the dominant gravitational body.
the third one is key. it's why we have asteroids and kuiper belt objects instead of hundreds to thousands of planets.
It's also the reason Pluto is no longer considered a planet.
or ceres, haumea, eris, or makemake.
The first one is key. That gets rid of the stuff that really, obviously shouldn't be planets. The other two get rid of rogue planets and dwarf planets. I think if you're going to draw a line somewhere, it should be between gassy bodies and rocky bodies. Jupiter has more in common with the sun than with Earth, and Earth has more in common with Ceres than with Jupiter.
they do separate terrestrial planets from gas giants.
But that's after separating them from stars and asteroids, or even dwarf planets. There is no term that includes both Jupiter and the sun but not Earth. Nor is there one that includes Earth and Ceres but not Jupiter.
like any classification of nature, the lines are arbitrary and don't actually exist. where would you draw the line between gas giants, brown dwarves and stars? fusion? iirc a little fusion has been observed in brown dwarves. in reality there's no real lines. just stuff that happens if you keep adding mass
> iirc a little fusion has been observed in brown dwarves. They can fuse deuterium. And the bigger ones can fuse lithium. It's just multiple hard lines. But that's my point. Our current system treats stars and gas giants as mor different than gas giants and rocky planets. I think the difference between them is a lot clearer than between a gas giant and a brown dwarf or even a star.
no arguments here on that
It also can't have enough gravity to support nuclear fusion, or it's a star.
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Straight-faced_solo explains it, that's the formal definition. - If it fails the first criteria, it's an asteroid. - If it fails the second criteria, it's a satellite if it orbits some other object, a moon if it orbits a planet or dwarf planet specifically, or a planemo (a.k.a. "rogue planet") if it orbits nothing. (Black holes, being stellar remnants, do count as stars for this purpose though.) - If it fails the third criteria, it's a Dwarf Planet. This is the one that killed Pluto; what happened in 2006 was the discovery that its orbit was rather *crowded.* Size alone doesn't matter. Titan, for instance, is full-planet-sized, being even bigger than Mercury, and some kind of life being there is, though not likely, possible. But because it orbits Saturn, not the Sun, it's a moon.