Full_Temperature_920 t1_j2e7j76 wrote on December 31, 2022 at 4:37 PM

Reply to comment by Scuka1 in eli5: back then, before astronouts goes to space, how do we know about thing like nonexistent of oxygen & zero gravity? by zetasstra

I'm assuming planets and other celestial bodies don't experience drag in space, so those definitely will keep orbiting their star until it expands and swallow them then? Assuming nothing flying through space impacts them with enough momentum to shift the course

Scuka1 t1_j2e9lzb wrote on December 31, 2022 at 4:52 PM

Well, in theory, if conditions don't change, an orbit remains unchanged forever.

However, in practice, in our Solar system for example, you've got planets orbiting the Sun, each at their own pace, and every planet is exerting some gravitational force on other planets as they pass each other by, making tiny changes in their orbits.

So, orbits do change over HUGE periods of time (but we're talking slight changes over millions of years), but they don't really decay.