Space Place Musings

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Narrator: Welcome to Space Place Musings, where an expert answers questions from our Space Place museum partners across the nation. I’m Diane Fisher of the New Millennium Program. Our expert is Dr. Marc Rayman, a scientist at the Jet Propulsion Laboratory.

Rayman: What’s our question today, Diane?

Narrator: This one is from the W.A. Gayle Planetarium in Montgomery, Alabama. They’re curious about Jupiter and Saturn. They’re called gas giants, so could you just fly straight through them?

Rayman: I can see why they might think you could. We think of a gas as something very . . . well, airy. We breathe air and fly planes right through it. So it makes sense to think that a gas planet must be like a big, airy cloud floating in space.

But take another look at Jupiter and Saturn—or pictures of them. Notice how round they are. You will never see a cloud on Earth so nearly spherical.

Narrator: So, what makes them round?

Rayman: Well, the short answer is—gravity. Gravity causes all matter to be pulled toward all other matter. When the planets were forming, the solar system was a big, swirling disk of gas and dust, with the newborn Sun at the center. Bits of dust and clouds of gas clumped together because of gravity, attracting still more matter, with the clumps growing larger and larger until there was no longer any stray material nearby for them to attract. The growing planets were like big solar system vacuum cleaners, sweeping up all the debris in their neighborhoods. And they became round because gravity pulls equally toward the center of large masses such as planets, so anything sticking out gets pulled back to make a ball.

Narrator: So that explains why planets are round, but if they’re just gas, it seems you could fly through them.

Rayman: No, because you also have to consider pressure. The bigger a planet becomes, the heavier is the material weighing down on its center. Think of how it feels to dive under water. Your ears start feeling the pressure a meter or so, perhaps a few feet, below the surface. The pressure you feel is due to the weight of the water above you. Even on Earth's surface, every square inch of your body experiences 14.7 pounds of pressure from the weight of the atmosphere above you. If you could dive down to the center of Earth, the pressure on your body would be about 3.5 million times as great! The center of Jupiter is more than 11 times deeper than Earth's center and the pressure may be 50 million to 100 million times that on Earth's surface.

Narrator: Ah. Certainly no plane or spaceship could withstand that kind of pressure.

Rayman: That’s right. Also, the tremendous pressure at the center of planets causes the temperatures there to be surprisingly high. At their cores, Jupiter and Saturn are much hotter than the surface of the Sun.

Strange things happen to matter under these extraordinary temperatures and pressure. Hydrogen, along with helium, is the main ingredient of Jupiter's and Saturn's atmospheres. Deep in their atmospheres, the hydrogen turns into a liquid. Deeper still, the liquid hydrogen turns into a metal!

Narrator: But what's at the very center of these planets?

Rayman: The material becomes stranger and stranger the deeper you go. Scientists don’t understand the properties of matter under the extreme environments inside Jupiter and Saturn. Many different forces and laws of nature are at work, and the conditions inside these planets are very difficult to create in a laboratory here on Earth. But you can be sure that you wouldn't be able to fly through these bizarre materials! As we now know, the gas giants are much more than just gas.

Narrator: Actually, even much less extreme conditions in space are hard to create in a laboratory on Earth, aren’t they?

Rayman: True. That’s why we need to test new space technologies and materials in the laboratory of space in order to know that they will perform well in those conditions. That’s what NASA’s New Millennium Program is for, to validate new, more capable, and less expensive technologies on test missions, before risking these new approaches on more expensive science missions.

Narrator: Well, Marc, you’ve cleared up one mystery about the nature of gas planets. Of course, now I’m even more dumbfounded about the weird stuff inside the cores of these planets. Thanks to all of you out there for tuning in to another session of Musings. Come back soon.

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