 Hi MIT, I have a question. You're just learning about the solar system, and I have a question about our gas giants. How come our gas giants stay in the sphere, instead of the gas just blowing around everyone in space? Hope you answer my question. Bye! Hello, my name is Anna Freebull, and I'm a professor here at MIT. I'm actually an astronomer, and I'm going to answer your question about space. You ask about gas giants, so large planets that have a gaseous atmosphere, and why they're in a sphere. It's mostly due to gravity. Gravity acts on matter in space, and acts on all objects in space, and it acts particularly over large distances. So in a gas giant like Jupiter, what's happening is that gravity pulls on all matter in the same way that a person on Earth is being pulled to Earth, and that's why we're not floating in space, but we can't stand on the ground. The same is happening in Jupiter. All the gas is just mass. It's little particles spread apart in the gas, rather than clump together in solid matter, like a rock for example. So what's happening then is gravity is pulling the material towards the center of Jupiter, and there is some gas pressure from the atmosphere, for example, and some heat also that acts outwards, that wants to push things away. When things get hot, they want to expand. And the reason why everything stays in a sphere is because gravity is pulling things in, and this pressure from the planet is pushing things out, and it keeps everything in a nice equilibrium. And the result of that is that it is actually a sphere because the force of gravity acts in the same way, in the same amount in all directions. So if you sit in the middle of the planet and you have a whole bunch of strings in your hand that are attached to all points around you, behind you and in front of you on the planet, those strings all have to be equal. If you imagine you were sitting in a cube and gravity is pulling things in and the pressure is pushing things out, then that would actually disrupt the cube because the force is not equal in all directions. If you have a shorter string right to the flat part of the cube in front of you and you would have a longer string, you would need a longer string to the corner of the cube. So in order to keep things stable and nice and not floating around in space, you would need to pull in the string going to the corner until it has the same length to the string that was going to the front of the cube. And so if you do this for all the points around you, you would end up sitting in a ball in a sphere again. And so that's why everything, even when it's made from gas, as long as there's enough mass where gravity can act on, is nice and contained in a big ball.