Internal Atmospheres

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I've been wondering this for the past week or so, but couldn't find any information on the subject. But does anyone suppose it's possible that a planet or moon that is fairly hollow (sponge-like even) could have just enough oxygen (or any other gas) to sustain an atmosphere, yet have it limited to below the planet's surface?

some have theorized that there is a whole 'nother civilization at the core of the earth that can only be accessed via the North Pole.

And thats where all of the flying saucers come from.

People who have espoused that generally reside in rubber rooms.

But anythings possible, but ..

you're talking about a rocky planet (as opposed to a gas giant) that has an outer layer of rock and or soil, but has one or more layers of earth-like atmosphere beneath that rocky crust.

Thats a highly unlikely thing to evolve in nature for the simple reason that a planet would tend to coalese in such a way that the heavier denser stuffs ends up near the core and the lighter stuff ends up on the surface. So a layer of gaseous atmosphere is unlike to form BENEATH a layor of rock and or soil- (unless some really advanced aliens were to engineer a whole artificial planet ofcourse).

I think some of Earth's atmosphere came from outgassing and differentiation of lighter elements. Although much of the oxygen did come from photosynthesizing orgasms in what's known as the "oxygen catastrophe" (catastrophic if you're a one-celled little organism who can't handle oxygen!)

Okay, so the possibility you're asking about, it's just incomplete outgassing and the planet is left spongy.

I have to agree with the other posts that gravity would pull in the heavier, denser elements toward the center and the lighter gasses would rise outward. I suppose anything is possible (aliens, huge gas pockets, weird planetary formation) but this is highly unlikely.

Planetary scientists seem to think that hollow planets would not be stable (as far as I can tell). Spongy planets strike me as slightly more likely, but not much. Plus, the surface layer would have to be really deep, or else the atmosphere would all escape whenever the planet was hit by an asteroid.

Some asteroids (and comets) are small enough that they can be more-or-less like a loose rubble pile. But they are way, way too small to hold an atmosphere. (There are several bodies in our solar system that are spherical due to gravity, but don't have an atmosphere, including our Moon.) Anything large enough to have an atmosphere would definitely be large enough that gravity would deform it into a nearly spherical shape, so even if you magically made a giant sponge the size of the Earth, it definitely wouldn't resemble a sponge in the center.

You could think about a sponge-like layer on the surface, but if gravity were too low to keep the atmosphere, it would escape anyway, and if gravity were high enough to keep it, you wouldn't need a sponge layer in the first place.

Thanks for all the replies!

I know it's unlikely that a planet like the one I'm describing is highly unlikely to occur naturally without collapsing into a somewhat solid spheroid first, but I find hypotheticals like this interesting because the thought of a subterranean atmosphere interesting.

It also reminds me of these articles I found a while back explaining what a cubic Earth would be like if it's existence were possible, for those interested:

http://possiblywrong.wordpress.com/2011 ... re-a-cube/

http://www.askamathematician.com/2011/0 ... -possible/