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Say we had a planet which was a gas giant. Is it possible that at the core of the planet where meteors, asteroids, and comet debris had collected that there could be a layer of atmosphere similar to that of Earth's?

If this could happen, could there be a temperature friendly to super strong multicellular organisms.

Also, what would it take to leave the atmosphere?

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    $\begingroup$ Is it okay that I added the science-based tag (and the others)? I'm assuming you want a science-based answer. . . $\endgroup$ – HDE 226868 Nov 29 '14 at 14:29
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    $\begingroup$ That is not a problem. $\endgroup$ – Kcronix Nov 29 '14 at 23:11
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    $\begingroup$ There was a bit in The Host about a sentient race of quasi-aquatic creatures that basically swam in the denser atmospheric regions of a gas giant. Their evolution wasn't gone into in any great detail. Your biggest hand-wave would be explaining how life (carbon-based or otherwise) developed in a mass that would be predominantly H/He and relatively little carbon or silicon, most of that concentrated in a temperature band in which most carbon-based chemical reactions are impossible. $\endgroup$ – KeithS Oct 26 '15 at 22:17
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I don't think we're going to find any evidence (like TimB did for this question) that life does exist on extrasolar gas giants, but we can at least use some logic to figure it out.

No.

First, the cores of gas giants are nothing like asteroids, comets, or even terrestrial planets. Jupiter's core is thought to consist of rock, surrounded by metallic hydrogen - in a liquid state, known as a supercritical fluid. Temperatures there are thought to reach a whopping 36,000 K - just at the outer edges - and pressures are thought to be about 3,000,000 Pascals, much greater than on Earth. Here's a guide to the interior of Jupiter (way too warped to put here).

Saturn's core isn't much different: a ball of rock and ice surrounded by hydrogen and helium at enormous temperatures and pressures. Uranus's core is only at about 5,000 K and a measely 800,000 Pascals, but that's still very harsh conditions - too harsh for life to survive. Neptune is much the same. Any extrasolar gas giants probably have very similar internal structures.

there could be a layer of atmosphere similar to that of earths.

No. The conditions anywhere near the core are fairly bad.

Also what would it take to leave the atmosphere?

You're looking for escape velocity. At a distance $r$ from a body with mass $M$, the escape velocity is $$v=\sqrt{\frac{2GM}{r}}$$ Given that the cores are generally many more times massive than Earth (though Neptune and Uranus may be exceptions) and are also bigger than Earth, I'd say that the answer would be that it would be very, very hard (i.e. impossible), taking into consideration the temperatures and pressures down there.

Assuming, however, that there somehow is life in the core of this planet, and some of the life forms want to get off the core, here's what they'd face when trying t build and fly a spaceship off the planet:

  • Temperature. Iron melts at 1811 K and boils at 3134 K - and the temperatures here are an order of magnitude higher than that! I haven't been able to find figures for steel, but I'm guessing it wouldn't do you any good here. Copper, brass, and just about any other metal you can think of would most likely be in some sort of gaseous state.
  • Pressure. Same problems here as with pressure. Landers on Venus, with its surface air pressure of 9.2 MPa, have been crushed in a very short period of time. If the temperature didn't get any materials on Jupiter's core, the pressure would.
  • Drag. Materials aside, you're going to have to get through tens of thousands of miles of gases here. I can't find the exact figures for the atmospheric gases, but I would assume that their density would make it very tough to get anywhere. A lot of energy would be lost to atmospheric friction, not only taking away energy but heating up the spacecraft.

TimB recently brought up a good point in a comment:

Hmm, the thing this answer misses is that there is a band as you come further out of the atmosphere where the pressure and temperature are actually reasonable. The question then arises as to whether life could evolve there.

We did have a question a while back about whether or not life could form on a planet with multiple gas layers. There was a division over this: TimB said it was unlikely for anything bigger than bacteria, and I came up with a whimsical scenario involving pufferfish polyps.

Bacteria could definitely live up somewhere in the upper atmosphere of a gas giant. I don't think there's any doubt about that. But any life in the gas giant's atmosphere would have to be high up, and therefore either flying or lighter than air. The first is possible but only if the creature was introduced pre-evolved. The second is less likely. Bacteria are your best shot.

Also, the life-forms would have to breathe an odd mixture of gases. Their best bet would be hydrogen and helium, neither of which is conducive to life, although they could also go for methane, trace amounts of oxygen, or ammonia-based compounds. There's also a bit of water, although that would be useless for respiration. Quite frankly, I don't think complex life could evolve in the atmosphere - or anywhere on a gas giant!

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    $\begingroup$ I don' think the OP is looking for escape velocity, but what challenges there would be in moving through the other layers above the imagined Earth-like layer. That part of the question is probably moot given the first part of your answer. $\endgroup$ – Neil Slater Nov 29 '14 at 16:47
  • $\begingroup$ @NeilSlater Good point; I can expand a little. $\endgroup$ – HDE 226868 Nov 29 '14 at 16:49
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    $\begingroup$ @Kcronix Is it possible for life to exist? No. $\endgroup$ – HDE 226868 Nov 29 '14 at 23:14
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    $\begingroup$ Hmm, the thing this answer misses is that there is a band as you come further out of the atmosphere where the pressure and temperature are actually reasonable. The question then arises as to whether life could evolve there. $\endgroup$ – Tim B Nov 30 '14 at 19:31
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    $\begingroup$ Ok how is the core partially made of ice if the temperatures are so high? $\endgroup$ – James Dec 1 '14 at 20:00
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Actually, it has been suggested that complex, multicellular life could evolve to float in the atmosphere of a gas giant. From single cells floating in hospitable bands of the atmosphere, we could reasonably expect to go from those to multicellular organisms capable of moving about under their own power.

As to whether such life could leave the atmosphere... This is a very complex question. It would be necessary to construct infrastructure that could float in the habitable bands of the atmosphere - anything too heavy could drop down out of reach, and anything too light could float up out of reach. However, if the materials were available, it may be possible for beings in these conditions to explore both upwards and downwards, and potentially even leave the atmosphere entirely.

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  • $\begingroup$ Manta's Gift by Timothy Zahn. :) $\endgroup$ – Jay Vogler Dec 16 '14 at 2:37
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As others have mentioned, it could be possible for life (as we know it, maybe, kind of) to survive in Jupiter's atmosphere. Don't forget, however, that Jupiter's magnetosphere also produces a LOT of bad radiation. That's a big theoretical obstacle to any kind of human colonization of Jupiter's moons, and it would be a really big hazard for any kind of life in or around the planet.

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    $\begingroup$ Monocellular life can be extremely radiation tolerant. Something that has a life cycle measured in hours is easily able to keep ahead of radiation damage. ISTR reading of cyanobacteria being a problem for swimming-pool nuclear reactors. They photosynthesize off the cherenkov radiation! $\endgroup$ – nigel222 Jan 7 '17 at 11:42
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In the novel 2061: Odyssey Three from Arthur C. Clarke in the end there is the consciousness floating to the surface of jupiter and saw clouds who couldnt make fire and hence were compelled to stay on a nomadic civilizational status.

This was taken into consideration when deciding whether to deploy the monoliths on that planet.

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