What Planet Would Float if Dropped in a Big Ocean?

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If the planet were dropped in a big ocean, its mass would depend on whether it would float. Find out what planet would float if dropped in a big ocean with help from an educational professional in this free video clip.

Part of the Video Series: Moons & Planets
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Video Transcript

Hi, my name is Eylene Pirez, and I'm an astrophysicist, and this is, "Which planet will float if dropped in a big ocean?" So the first speculation here is could we even have an ocean big enough to drop a planet in? Believing that we could, and we had regular water and the gravitational pull of the earth and the ocean was big enough to drop a planet, we will have to see which planet has a very light density, and this is actually a common myth, and the one that we're talking about is Saturn, and generally people say, oh if you put Saturn in a tub it will float. This is, this is completely untrue, and I will show it, and the reason they use this argument is to show density. So, how do we look at density? So the density of a planet is the mass of the planet divided by the volume. But as you can see here, we're taking the total mass and the total volume. What's happening in planets like Saturn? Planets like Saturn are made out of layers, so the layer in the middle is extremely, extremely dense, and then the outer layers are very, very, they're very low in density. So therefor, the density is not averaged throughout, and here we're just averaging out the entire density, so we're looking at the planet and we're simplifying it as if it was to be like a ping pong ball, this calculated density, the average density for Saturn, if we were to think of Saturn as a ping pong ball. So the mass of Saturn is 5.68 times 10 to the 26 kilograms, and the volume formula is four-thirds pi, and is the radius of Saturn to the cube. So then we'll have 5.6 times 10 to the seven, sorry, 10 to the seven cubed. If we calculate this density we will have 772 kilograms per meter cubed, and this is the density of Saturn. Now what's the density of water? In order for something to float, the density has to be lower than that of water, otherwise the object will sink. Well the density of water is a thousand kilograms per cubic meter. So yeah, indeed Saturn has a lower density as water, but that is taking the average density, it's not taking Saturn as it actually is, it's assuming that Saturn is a perfect ball with the mass being distributed equally inside the volume. So no, Saturn will not float in a pool of water. But if you were to take the average mass and the average volume, you could visualize it as low density enough to float on water. My name's Eylene Pirez, and I'm an astrophysicist, and this is, "Which planet will float in a big ocean?"


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