Eli5 on why do planets spin?
In: 1322
Quick Answer: It would be harder for them NOT to, if you think about it. Picture all those videos of astronauts letting go of an object while in a space station and the thing sloowly drifts and tumbles. Imagine how hard it would be to keep an object perfectly still from letting it go.
Longer Answer: When a cloud of objects gets accelerated in toward a central source of attraction, it tends to swirl as it moves to the center, like the water getting sucked toward a drain does. And the solar system was first formed like that – a bunch of gasses got close enough for their gravity to start “clumping” them together toward the center. As they do that, the cloud starts to spin. Then later that cloud of matter starts to clump tighter and tighter, forming a few solid lumps as the matter gets compressed tightly enough. The big one at the center becomes the sun and the littler ones around it become planets, but because the cloud they were formed from was already swirling around the center to begin with, when it compressed down into a solid ball, that ball already had quite a bit of spin momentum. This is also why the planets all spin the same direction – except for two
And those two exceptions, Venus and Uranus (Venus spins backward compared to the rest, and Uranus spins “sideways” compared to the rest, are immensely interesting because of it.) There hasn’t been a definitive answer yet for how they got that way. One possibility is that Venus might be the result of a massive impact between two planets like what happened to the Earth that created the Moon, if the impact was just right it could flip the planet upside down causing the spin to flip. Another possibility is “foreign object capture” where maybe Venus wasn’t originally part of the solar system but was an external planet that flew by and got captured by the Sun.
Latest Answers