TIL that it takes less energy to launch something out of the solar system than directly into the sun. Apparently its because the massive gravity of the Sun causes objects to orbit instead of pulling objects into itself. Why?

Question

TIL that it takes less energy to launch something out of the solar system than directly into the sun. Apparently its because the massive gravity of the Sun causes objects to orbit instead of pulling objects into itself. Why?

In: Physics

Answer 1

Imagine you’re on a frictionless roller coaster stuck between two huge hills. You can make it about 80% of the way up before stalling and then rolling backwards down and up the other hill where you make it 80% up again before coming to a stop and starting the cycle over (in a stable ‘orbit’). If you want to get over the hill, you need a little extra boost. So you strap some rockets on the back (you know, those ones that you always carry around and everyone make fun of you, saying “you’ll never need them!”) and light ‘em up!* This gives you enough extra energy to clear the hill (your gravity well) and move on (exit the solar system).

Now, if instead you wanted to roll around near the bottom of the hill (orbit the sun) or even come to a stop (fall into the sun), you could fire your rockets in the opposite direction to slow down. But since you have a lot of momentum already, you have to fire a lot more rockets to slow down than you did to boost over the hill.

*If you’re smart you’ll light them just when you reach the bottom and you’re going the fastest, as this will give you the most ‘boost’ (see [Oberth effect](https://en.m.wikipedia.org/wiki/Oberth_effect) )