The Closest Gas Giant: Why is Jupiter so Big?

[Nim]

How I understand it, the four inner planets are rocky planets because the Sun boiled off most of their atmospheres, while the planets past Mars retained there's.

I was wondering if the reason why Jupiter is so big is because it is the closest planet to Mars, so it caught most of the atmosphere that was boiled away by the Sun. Plus, the planets get smaller and smaller after Jupiter. Although maybe that has more to do with the density of the disc near the edges when the planets were forming.

 

[russ_watters]

My guess would be its the density of the disc. Not sure though.

 

[FZ+]

I believe the current theory to the creation of the gas giants relies on turbulence developing in the disc, swirling some gases into clumps. In this case, the fact that Jupiter is the innermost is probably because Jupiter was a disturbance that started in a patch of high density gases.

I don't think the atmosphere of Mars is a significant factor.

 

[Mentat]

Actually, Nim, it is held that planets have to be very large, in order to produce enough gravity to hold in lighter gases. Earth is only large enough (IIRC) to hold in Oxygen and heavier gases/elements.

So, the atmospheres were not blown off of other planets onto gas giants, but rather each planet developed it's own atmosphere as it was forming, and the bigger ones could hold in lighter gases.

Jupiter, btw, is considered to be a "brown dwarf" star, which is star that never "ignited".

 

[drag]

Originally posted by Mentat
Jupiter, btw, is considered to be a "brown dwarf" star,
which is star that never "ignited".

Nope, as far as I remember it'll have to be 8-10 times
more massive for that.

Peace and long life.

 

[Nereid]

Nim How I understand it, the four inner planets are rocky planets because the Sun boiled off most of their atmospheres, while the planets past Mars retained theirs.

Close. The inner planets formed in a region where the volatiles (water, methane, ammonia, etc) had been 'boiled off' while the proto-solar system disk was collapsing; their atmospheres came later, from comets (tho' not the Earth's oxygen Mentat, that came much later, from plants).

All the planets were formed by collisions (rocky planets) or gravitational accretion (gas planets) of planetesimals.

Nim I was wondering if the reason why Jupiter is so big is because it is the closest planet to Mars, so it caught most of the atmosphere that was boiled away by the Sun. Plus, the planets get smaller and smaller after Jupiter. Although maybe that has more to do with the density of the disc near the edges when the planets were forming.

Jupiter, like the other gas giants, could grow bigger than the rocky planets because there was much more material from which it could form (all those volatiles).

The planets get smaller and smaller after Jupiter because of the way the remaining gas, dust, and planetesimals were swept up by the growing planets.

Here's a link that gives a good overview:
http://www.pha.jhu.edu/~akir/Seminar/seminar.html

Mentat Jupiter, btw, is considered to be a "brown dwarf" star, which is star that never "ignited"

No, it's still a planet. Although the terminology is somewhat inconsistenly applied, the star/planet distinction refers to the formation process, not the mass, nor whether ignition took place or not. Stars form by the collapse of a gas/dust cloud; planets by accretion.

 

[drag]

Greetings !

We have to remember that that's the way things happened
in our solar system, but we've already seen many that
acted otherwise.

Originally posted by Nereid
No, it's still a planet. Although the terminology is somewhat inconsistenly applied, the star/planet distinction refers to the formation process, not the mass, nor whether ignition took place or not. Stars form by the collapse of a gas/dust cloud; planets by accretion.

Well, isn't that more of a relative definition, after all
a star can also be orbiting other stars/objects as well
as turning aroung the galaxy center and a planet can
also form individualy without anything nearby to rotate
around, if the amount of gas is too small. Right ?

Live long and prosper.

 

[Nereid]

drag wrote: Well, isn't that more of a relative definition, after all a star can also be orbiting other stars/objects as well as turning aroung the galaxy center and a planet can also form individualy without anything nearby to rotate around, if the amount of gas is too small. Right ?

Definitions can be somewhat arbitrary. Among those who work together, or otherwise form a community, you usually find that the terms they use settle down to have fairly narrow ranges of meanings (unless they're politicians, of course!).

Stars form by the collapse of a gas/dust cloud; planets by accretion

That's what astronomers generally mean when they use the terms 'star' and 'planet'. Certainly, stars may form in pairs (the collapse of two blobs of gas, or a cloud which formed two centres), and may form in a galaxy or globular cluster.

An object which forms from a very small gas cloud would be called a brown dwarf. A number of isolated brown dwarfs have been observed, though it's not always clear if they formed in isolation, or were ejected from a binary.

 

[Mr. Robin Parsons]

Originally posted by Nereid
No, it's still a planet. Although the terminology is somewhat inconsistenly applied, the star/planet distinction refers to the formation process, not the mass, nor whether ignition took place or not. Stars form by the collapse of a gas/dust cloud; planets by accretion.

So the fact that Jupiter gives off lots more heat, then it gets from the Sun, seems to, in your mind, not have anything to do with the distinction 'tween stars and planets, Huh?

 

[LURCH]

Originally posted by drag
Greetings !

We have to remember that that's the way things happened
in our solar system, but we've already seen many that
acted otherwise.

In fact, these other systems have caused us to re-evaluate the current model. Many of the extrasolar planets so far discovered are planets several timea the size of Jupiter with orbits smaller than Venus. This has lead to the idea of planetary migration, which proposes that Jupiter and possibly the other gas giants formed close to the Sun and then moved outward much later.

I don't really buy that theory yet, but it is gaining credibility. Personally, I think the inner planets are rocky because of the composition of the protosolar accretion at the very beginning. The disk was formed buy gravitational attraction, and so it would seem (to me, at least) to make sense that the heavier elements were closer to the center, sort-of "settled to the bottom". Meanwhile, the lighter elements that we normally think of as gasses would float to the top, leaving them out near the edge. I am hoping that the mission to Pluto will help confirm this idea.

 

[Nereid]

Originally posted by Mr. Robin Parsons
So the fact that Jupiter gives off lots more heat, then it gets from the Sun, seems to, in your mind, not have anything to do with the distinction 'tween stars and planets, Huh?

Just telling it like it is!

Who sets the rules for how language is used? Let's all vote for Mr. Robin Parsons!

First order of business, Madame Chair (of the International Astronomical Union), motion to refer all questions of nomenclature to Mr. Robin Parsons for his esteemed, absolute ruling.

 

[Mr. Robin Parsons]

Originally posted by Nereid
Just telling it like it is!
Who sets the rules for how language is used? Let's all vote for Mr. Robin Parsons!
First order of business, Madame Chair (of the International Astronomical Union), motion to refer all questions of nomenclature to Mr. Robin Parsons for his esteemed, absolute ruling.

To whom it might/and/or/does concern, I would respectfully desist from the nomination, as it is deleterious to my current reputation to have such a nominator at hand.
Thanks, one and all!

 

[Nereid]

And did you know, those perfidious astronomers, they wanted to demote Pluto! They had this totally unreasonable, irrational idea that just 'cause
- there are lots and lots of satellites that are bigger
- it's merely the largest of a class of objects, numbering >1,000 (the Plutinos, EKB objects, SDOs, ... take your pick)
- Ceres* doesn't get to be called a planet
- etc, etc, etc
it didn't deserve to be called a planet. I mean, just look at it - doesn't it look like a planet to you?

Girl, they sure know how to hurt a planet's feelings.

*the largest asteroid. Like the planets, asteroids orbit the Sun. The main belt asteroids' orbits lie between Mars and Jupiter. >200,000 have been observed (only ~10,000 have names). If Ceres isn't a planet, why should Pluto be?