What Defines the Limits of Anomalous Planets?

[Loren Booda]

1. What is the smallest possible self-gravitating, gaseous astronomical object?

2. What is the largest possible terrestrial astronomical object?

3. Does there exist a star-free, orbiting system of planets?

 

[mathman]

I can't answer your first two questions. As for the third, an orbitng system requires a massive (compared to the planets) central body for the planets to orbit around. It doesn't have to be a star - it could be a black hole.

 

[Nereid]

1. What is the smallest possible self-gravitating, gaseous astronomical object?

2. What is the largest possible terrestrial astronomical object?

3. Does there exist a star-free, orbiting system of planets?

"It depends"

For example, within our solar system there are four 'gas giants' - Jupiter, Saturn, Uranus, and Neptune. It is very likely that all four have a solid core of some kind. Do such planets count as objects in Q1?

Perhaps 'smallest' refers to size, not mass? One would then think of a white dwarf or neutron star, but would they qualify as 'gaseous' (Q1)?

Similar considerations for Q2: 'large' = mass, size, or something else? How different from the Earth would a planet have to be before it would no longer be considered 'terrestrial'?

On top of these definitions, there's also the question of 'that could be formed in the universe'? vs 'a thought experiment into the bulk properties of matter, and gravity, including chemistry and geology'?

The easy answer to Q3 is "none have been observed to date". But perhaps that wasn't the question.