But it spins, fast , so at the equator the centrifugal force flings the material outward a bit, causing it to be wider there. So, the ratio of centrifugal force to gravity is higher on Saturn than Jupiter, making the gorgeously ringed planet more oblate. You can tell a lot about a planet just by measuring a few basic things about it, like how big it is, how fast it spins, and what shape it is.
So, I guess I have to forgive my brain after its initial outburst. The follow through was pretty good. Just to start, spinning the Earth faster would mean much stronger hurricanes. Also, the energy it would take to get our planet spinning faster would melt the surface down to the crust. So, there are some issues with it. Also, correction: I did the math wrong initially. In other words, the giant planet radiates nearly twice as much energy as it receives from the Sun, and almost half of the total energy that Jupiter loses must come from its interior.
That essentially meant that the planet had to be unexpectedly hot inside. According to the widely accepted nebular hypothesis, the Sun and planets formed together during the collapse of a rotating interstellar cloud called the solar nebula. Further out, the planets formed out of a whirling disk of the same material.
If the nebular hypothesis is correct, and the whole solar system originated at the same time, then you might expect Jupiter to have a similar chemical composition to the Sun. To a first approximation, the abundance of the elements in the giant planet does indeed mimic that of the Sun, with a predominance of the lightest element hydrogen. It is the most abundant element in most stars, in interstellar space, and in the entire Universe. The second most abundant element in both Jupiter and the Sun is helium, and hydrogen and helium together account for the low mean mass density of both objects, at 1, and 1, kilograms per cubic meter respectively.
Observations with even a small telescope show that Jupiter is not a sphere. It has a perceptible bulge around its equatorial middle and is flattened at the poles.
The outward force of rotation opposes the inward gravitational force, and this reduces the pull of gravity in the direction of spin. Since this effect is most pronounced at the equator, and least at the poles, the planet expands into an oblate shape that is elongated along the equator.
That's the force that holds stuff together in space. When a forming planet is big enough, it starts to clear its path around the star it orbits. It uses its gravity to snag bits of space stuff. A planet's gravity pulls equally from all sides. Gravity pulls from the center to the edges like the spokes of a bicycle wheel. This makes the overall shape of a planet a sphere, which is a three-dimensional circle. While all the planets in our solar system are nice and round, some are rounder than others.
Mercury and Venus are the roundest of all. They are nearly perfect spheres, like marbles. Saturn and Jupiter are bit thicker in the middle. As they spin around, they bulge out along the equator. Why does that happen? When something spins, like a planet as it rotates, things on the outer edge have to move faster than things on the inside to keep up.
This is true for anything that spins, like a wheel, a DVD, or a fan. Things along the edge have to travel the farthest and fastest. Along the equator of a planet, a circle half way between the north and south poles, gravity is holding the edges in but, as it spins, stuff wants to spin out like mud flying off a tire. Saturn and Jupiter are really big and spinning really fast but gravity still manages to hold them together. That's why they bulge in the middle.
0コメント