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Tuckerfan
2006-Jun-14, 09:39 AM
When I was a kid, I read a book that to illustrate Saturn's composition, stated that if you had a tank of water large enough to hold Saturn, the planet would float. I'm thinking that they were ignoring the effects of gravity on such a situation. So, putting gravity back into the equation, what happens? Would the water's gravitational field pull Saturn apart? Or would Saturn suck up the water, or would it float just as pretty as you please?

Ronald Brak
2006-Jun-14, 09:50 AM
I bet the teachers just hated you at school.

HenrikOlsen
2006-Jun-14, 09:54 AM
You'd end up with a somewhat larger Saturn with more water in the interior.

grant hutchison
2006-Jun-14, 02:05 PM
The self-gravity of a tank of water big enough to float Saturn would be very large. It would therefore need a very, very massive object to rest on, since we need to have a gravity vector directed towards the bottom of the tank in order to create a water surface on which floating can occur.
Anything massive enough to overcome the water's self-gravity and make it lie flat would presumably overcome Saturn's self-gravity, too, turning it into a splodge rather than a planet.
Or, we could just have a very big sphere of water, held together by its own gravity, and big in comparison to Saturn: but then the tidal forces from the water-planet would pull Saturn apart as it approached.

Grant Hutchison

loglo
2006-Jun-14, 02:58 PM
I guess that analogy just doesn't hold water. :D

JohnW
2006-Jun-14, 03:39 PM
I feel a grant application coming on.

Saluki
2006-Jun-14, 04:22 PM
The point they were trying to make is that Saturn's density is less than that of water. Unfortunately, they chose a very bad analogy to make the point.

mike alexander
2006-Jun-14, 11:28 PM
This particular analogy has been around for at least half a century that I know of (it was in books when I was a small kid). I'm reminded of Steve Gould's essay "The Case of the Creeping Fox Terrier Clone", where he traced the use of the 'fox terrier sized' Eohippus analogy all over the place, even to finding mutations in the description which then moved out into lives of their own.

Tobin Dax
2006-Jun-15, 12:29 AM
The point they were trying to make is that Saturn's density is less than that of water. Unfortunately, they chose a very bad analogy to make the point.

Then stay away from astro classes at UIUC. :)

snarkophilus
2006-Jun-15, 03:36 AM
Actually, at the point where you have enough water to hold Saturn, it doesn't even behave like liquid water any more. There's enough pressure to put it into a supercritical fluid phase, or maybe a weird solid phase. Anyway, water is usually less dense in these phases than in the liquid phase, so it's hard to say what would happen. If it was still denser than Saturn, much of the planet would spread out across the surface of the water, but I think that a lot would dissolve in it, too.

Keep in mind that density is going to change with depth, too, both for the planet and for the water. Probably the two will mix to some extent. You could get stratification. It might actually depend on how you put them together.

You can avoid the problem of having Saturn getting ripped apart by tidal forces as it approaches a big sphere of water by instead throwing a lot of little spheres of water at it. Done properly, you might end up with the same result as what was intended in the original analogy.

ToSeek
2006-Jun-15, 02:44 PM
This particular analogy has been around for at least half a century that I know of (it was in books when I was a small kid).

I remember a literal-minded "Saturn in a bathtub" illustration from one of the astronomy books at my elementary schoo.

Saluki
2006-Jun-15, 03:13 PM
I remember a literal-minded "Saturn in a bathtub" illustration from one of the astronomy books at my elementary schoo.

There is a lot of misinformation in elementary science texts. I struggle with my kid's science homework because the "correct" answer is usually overly simplified and not correct at all.

I remember a discussion between my (then) 7 year old daughter and 5 year old son about how the Sun produces its energy. My son was certain that it was "electric", like a light bulb. My daughter believed it was "on fire", because that is what her teacher had told her. Eventually, they came to a compromise and decided that to be that hot, it must be both electric and on fire.

grant hutchison
2006-Jun-15, 03:29 PM
Some here may appreciate the avatar (http://www.shatters.net/forum/profile.php?mode=viewprofile&u=912) used by chaos syndrome, over on the Celestia forum. :)
He raytraced it himself, IIRC.

Grant Hutchison

farmerjumperdon
2006-Jun-16, 01:37 PM
If it was still denser than Saturn, much of the planet would spread out across the surface of the water, but I think that a lot would dissolve in it, too.

AHA! So it might be more like a humongous fizzy.

We should suggest it for Letterman's Will It Float segment. And warn them that they will need a much bigger studio.