Why are planetary orbits elliptical and not circular?


Why are planetary orbits elliptical and not circular?

In: 20

Part of the answer is planets are not just orbiting the sun, but they’re orbiting each other, but that’s not the whole story.

Think of it as the planet is actually falling into the sun, it just doesn’t hit the sun because it’s moving in a direction that is not towards the sun as well (perpendicular to the line between the planet and the sun).

If you drop a planet from standstill, it will hit the sun. If you push a planet a little bit, it will fall towards the sun, but some of that push will be enough to cause it to miss the sun, even if by a little bit. If it misses the e sun, it will slingshot around and come back to its starting position (an elliptical orbit).

Now if you push a planet with the exact perfect force, it will orbit in a perfect circle. Anything more, or less than that, will form an ellipse.

Because a perfectly circular orbit is not only very hard to occur by chance but even if it was it would not remain as such unless there were zero perturbations from other bodies acting on the orbiting bodies which is impossible. In fact the orbits of the planets in our solar system being as close to circular as they are is pretty impressive.

There is an infinite numbers of elliptical orbits and only one exactly circular orbit (in a given plane) which means circular orbits are incredibly rare.

Like some others have said, for most star systems that have multiple planets orbiting a sun one planet or another may have some substantial gravitational force that will pull another planet slightly put of orbit. This will most likely permanently alter the planets orbit. If you want something that will blow your mind, the sun and Jupiter orbit a point called the Barycenter which is just outside the sun’s surface.

A circle is an ellipse and a very specific one. Just like how a square is a rectangle, but not all rectangles are squares. There’s many different conditions that will form an ellipse but only one perfect condition to make a circle. Since there are more ways to make an ellipse that is non-circular, that is what will happen the vast majority of the time.