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Drakheim
2004-Feb-20, 03:35 PM
Of a rocky planet around the size of Saturn or Jupiter developing?

Mainframes
2004-Feb-20, 06:36 PM
Probably depends on the composition and size of the dust and gas cloud it's parent star forms from.....

Ut
2004-Feb-20, 07:09 PM
Define "size"...

Drakheim
2004-Feb-20, 07:33 PM
Raidus I guess? Basicly blow earth up to the size of Jupiter.

Taibak
2004-Feb-20, 08:51 PM
Raidus I guess? Basicly blow earth up to the size of Jupiter.

Is that possible? If you had an object with the mass of the Earth but the radius of Jupiter, wouldn't it collapse under its own gravity? It seems like you'd either have a diffuse cloud of dust or a very thin hollow shell. The former seems to be how planets form regardless while the latter just doesn't seem stable.

Sirius
2004-Feb-20, 09:10 PM
I personally don't beleive that planets can form on their own.... Beleive what you will. (I don't want to get into any arguments)

aurora
2004-Feb-20, 09:15 PM
Raidus I guess? Basicly blow earth up to the size of Jupiter.

Is that possible? If you had an object with the mass of the Earth but the radius of Jupiter, wouldn't it collapse under its own gravity? It seems like you'd either have a diffuse cloud of dust or a very thin hollow shell. The former seems to be how planets form regardless while the latter just doesn't seem stable.

I think what was meant was an object the size of Jupiter, but with the density of Earth.

Drakheim
2004-Feb-20, 09:15 PM
I personally don't beleive that planets can form on their own.... Beleive what you will. (I don't want to get into any arguments)

Not trying to start one with you, but how do you think they form?

Ut
2004-Feb-20, 10:50 PM
Just a guess, but I'd have to say that a rocky planet the volume of Jupiter would be quite the exotic. It would have to form from a HUGE cloud of silicate dust, after the gas from the solar nebula had been blown away.

Ok, a quick Google comes up with the following numbers.

Jupiter; Earth; Ratio (J/E)
Mass (10^24 kg): 1,898.6; 5.9736; 317.83
Volume (10^19 m^3): 143,128; 108.321; 1321.33
Volumetric mean radius (km): 69,911; 6,371.0; 10.973
Mean density (kg/m^3): 1,326; 5,515; 0.240

(I know it's a little hard to read.)

So, the Earth is 4.157 times as dense as Jupiter. That means that a rocky body of this size would have to be 7.89810^27 kg in mass. The universe is a big place. There could very well be a protostar somewhere that has that much rocky mass circling it. However, one does have to keep in mind that Jupiter, which is more massive than all the other planets and asteroids in the solar system combined, is made up largely of hydrogen and helium. So while it doesn't sound like an impossibility, there's probably not one next door or anything.

Brady Yoon
2004-Feb-20, 11:48 PM
I would say that the chances of having a rocky planet the size of jupiter is rare-because most of the material in the solar nebular is gas and dust. If there was a rocky planet the size of jupiter having the earth's density, it would way well over 1,200 times Jupiter. furthermore, all of the large extrasolar planets we have discovered are similar to Jupiter. But since the universe is so large, anything could be possible-maybe even a rocky planet the size of a star? who knows?

JohnOwens
2004-Feb-21, 03:06 AM
I would say that the chances of having a rocky planet the size of jupiter is rare-because most of the material in the solar nebular is gas and dust. If there was a rocky planet the size of jupiter having the earth's density, it would way well over 1,200 times Jupiter. furthermore, all of the large extrasolar planets we have discovered are similar to Jupiter. But since the universe is so large, anything could be possible-maybe even a rocky planet the size of a star? who knows?

No it wouldn't. The mass would only be a bit more than 4 times Jupiter's mass. Density of Earth is 4.157 greater, as above.
You might have a point if you said density ought to be greater than Earth's for similar materials, though, since I would think it should be compacted somewhat more at the center, or even if that's not big enough to bring about a more compact state, at least a greater percentage of the body would be near that peak density.

Brady Yoon
2004-Feb-21, 03:30 AM
No it wouldn't. The mass would only be a bit more than 4 times Jupiter's mass. Density of Earth is 4.157 greater, as above.
You might have a point if you said density ought to be greater than Earth's for similar materials, though, since I would think it should be compacted somewhat more at the center, or even if that's not big enough to bring about a more compact state, at least a greater percentage of the body would be near that peak density.

oops, what was i thinking when I said that!! i must have meant 1,200 times Earth's mass :D sorry about that. 1,200 times jupiter's mass would be like our sun #-o

eburacum45
2004-Feb-21, 10:47 AM
Lets take this stage by stage.

A very large rocky planet would have a very large surface gravity. This means that it would attract a very, very massive hydrogen component from the solar nebula it formed in; also a proportionately large amount of water.

Jupiter has formed around a rocky core of maybe 10 Earth masses; it has also retained a lot of water, but the great majority of the mass of that planet is hydrogen.
This would also happen in the case of your hypothetical massive rocky planet.

It would attract so much hydrogen it would become a brown dwarf, and gravitational compression would fuse the deuterium component, making the planet into a dim star.

Simulations of solar system formation suggest that rocky planets in the inner solar system can be as much as four times Earth Mass; such a planet would attract and keep a lot of cometary water and become a waterworld; (here is my fictional example (http://www.orionsarm.com/worlds/Panthalassa.html));

a very large rocky planet might be expected if a large gas giant migrates inward during the early stages of solar system formation because of friction with a thick solar nebula;
if such a giant is very close to the central star, its own gaseous envelope will boil off, like an enormous comet; the very closest examples of this type of world will lose all their volatiles, becoming a red hot, massive, rocky, high gravity world.

These hell planets have been labelled Chthonian planets; none has been observed definitely yet, (and we haven't got one in OA yet either)

Eroica
2004-Feb-21, 02:57 PM
A very large rocky planet might be expected if a large gas giant migrates inward during the early stages of solar system formation because of friction with a thick solar nebula;
if such a giant is very close to the central star, its own gaseous envelope will boil off, like an enormous comet; the very closest examples of this type of world will lose all their volatiles, becoming a red hot, massive, rocky, high gravity world.
What about the possibility of a gas giant migrating just close enough to the Sun for the solar wind to blow away its gaseous outer layers, leaving behind a large terrestrial world in a comfortable-for-life-as-we-know-it orbit?

According to Ask the Astronomer (http://www.astronomycafe.net/qadir/q1275.html), even the smaller rocky planets may once have had thick Jovian atmospheres, which were then blown away by the Sun's solar wind when the Sun entered its T Tauri phase. These T Tauri winds are a billion times denser than the current solar wind.