Distinguishing between gas giants and terrestrial planets with really big atmospheres

How do they distinguish between a terrestrial (rocky, like earth, mars etc) planet with a really big atmosphere, and a gas giant? Where's the dividing line? Gas giants are generally assumed to have a rocky core... it's thought Jupiter's rocky core is as big as earth.

Re: Distinguishing between gas giants and terrestrial planets with really big atmosph

I remember once hearing that Jupiter's surface was supposed to be kinda mushy...?

Re: Distinguishing between gas giants and terrestrial planets with really big atmosph

Blind guess: they just assume the former doesn't exist.



[edit] I mean, I'm assuming you're thinking of an Earthlike planet with an atmosphere, say, twice as thick as the planet itself. That kinda boggles my mind, personally.

Re: Distinguishing between gas giants and terrestrial planets with really big atmosph

Jupiter's surface is a metallic hydrogen slush, presumably.

Re: Distinguishing between gas giants and terrestrial planets with really big atmosph

I think that if you look at the ratio of mass of the "atmosphere" vs the mass of the mettalic hydrogen core of Jupiter and then compare it to the mass of Earth's atmosphere vs. it's terrestrial bits, the answer should be forthcoming. The Earth is the densest sphere in our solar system. The Jovian planets are so light in density that they'd float on water.

Sounds pretty distinguishing to me.

Re: Distinguishing between gas giants and terrestrial planets with really big atmosph

Man, I bet many a fistfight has developed over this topic.
Never mix alcohol and bad tempers with discussions of religion, politics, and planetary geology. People never learn.

Re: Distinguishing between gas giants and terrestrial planets with really big atmosph

Whether the atmosphere was formed from the primordial solar disc, or whether it was formed by outgassing from the rock. Earth has the latter, Jupiter the former.

Re: Distinguishing between gas giants and terrestrial planets with really big atmosph

The asteroid belt?

At least now that pluto isn't a planet thats true right?


Reminds me of a facebook group "When I was your age, Pluto was a planet!"

Re: Distinguishing between gas giants and terrestrial planets with really big atmosph

only for our solar system, several of the extrasolar planets found are 'hot jupiters', gas giants who orbit close to their star.

some theories suggest mercury was once a gas giant, and its atmophere got stripped away.