Why are gas giants and terrestrial planet compositions different?

Question

My current thought on this question is the distance from the sun. Heat from the sun and higher temperatures has kept mass amounts of helium, hydrogen and other gases out of our atmospheres. Gas giants are farther from the sun, and much much colder.

This is all I have so far, I obviously need some guidance. Please, I would love to actually understand the answer to this.

Answer 1

The point at which a proto-star becomes a T-Tauri star is the deciding factor, I think.  The earth must have once been a jovian world and had its atmosphere stripped away leaving only the core, otherwise it could never have accumulated so much heavy elements.  It's probably a very specific point in time that T-Tauri winds begin, because other stars have been observed to have jovian planets very close to their parent star.  They must have accumulated enough atmosphere and mass to withstand the extreme stellar winds at an early time in their parent star's deveopmental stage, before it started its thermonuclear reactions.  Our sun's T-Tauir stage must have started relatively quickly, before the inner planets had condensed fully.   I would speculate it has something to do with the heavy elements already present.  The sun is a second or third generation star, probably formed by the shockwave of a nearby supernova, compressing the gaseous nebula from which our sun and its siblings formed.  Heavy elements were injected into that system by the supernova, resulting in our planet's content of heavy elements; mostly silicon, oxygen, and iron.  Heavy elements are known to have an affect in the evolution of stars once they form.  It's not unlikely they also have an affect on their planets' evolution.

Good question and thought experiment, btw.  But really, no one knows.

Answer 2

I have heard of a theory that says that the gas giants are premature suns, although I don't remember the theory's name.

Answer 3

sorry

that's one of the Big Questions we have right now about planetary formation.  Unfortunately, we don't have a Big Answer to go along with it.

before we had any evidence of extra-Solar planets, the theory went basically like you said.  Light elements were not held by the gravity of the planet, etc, etc.  BUT, since we have seen several instances of stellar systems with gas giants in CLOSE orbits to their primary, we have had to invent more exotic theories...

Personally, I just think the Sun is an oddball who in his youth was a T Tauri variable and burned off the atmospheres of Mercury, Venus, Earth and Mars...  all our current atmosphere are at least SECONDARY.  This explains a few things, like the surface of Mercury, and its density, and why the Earth's atmosphere isnt methane and ammonia...

Answer 4

There are several really good answers, but I just wanted to put in a word. Terrestrial planets do not become gas giants because they don't have the gravity to keep hydrogen from being blown away into space.That is why the moon and Mars is so dry. The only ice water found on these bodies is at the poles because only the water that stays frozen indefinitely stays while all the water that melts and evaporates gets split into oxygen and hydrogen at one point or another and just floats away from the surface.

My 2 cents on why all the gas giants are in one section of the solar system is that is where the first matter began to clump togethor and grow. Once they got big enough (several times Earth's mass) they began attracting a LOT of the lighter elements in the accretion disk. This meant they got bigger while the later developing worlds had less matter to form out of... It does not have to do with proximity to the sun so much because very large gas giants have been found in other solar systems to be orbiting very close to its star.

I hope some of  this makes sense to you.

Answer 5

The general idea is that there is more thermal energy in the inner part of the solar nebula and progressively less as you go further out.  This means that in the inner solar system molecules like water, ammonia and methane tend to stay as gases and not produce grains and clumps and so on.  Around the orbit of Jupiter however the thermal energy drops to the point where these molecules can produce grains and lumps so there's a lot of this less dense material around to accrete into planets.  Jupiter and Saturn grew large enough to also pull in some of the hydrogen and helium from the solar nebula.  The inner planets accreted from grains containing oxygen and aluminium and silicon as well as iron and nickel and so on.  The solar wind then started blowing away all the lighter gases.

Answer 6

Hello!!

Gas giants and terrestrial planets have different compositions because they are different in kind. Gas giants are gas giants. Terrestrial planets are planets. So, common sense, they are really different.. :-)

:-)

Answer 7

God created them that way. If you don't believe that then scientifically idk, but I would think the sun kind of baked the planets closer to it and the other planets were too far away for the sun to heat up enough to solidify the gas planets.\.