I know how they stay in orbit but how do random planets and stuff have the exact speed needed to get to orbit? Is it pure chance or some phenomenon that speds them up or slows them down?
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There are a lot of speeds that will get you and keep you to orbit, theres no “exact speed.” For the most part its chance.
there isnt an “exact speed” to stay in orbit, just any specific orbit. so at the start of the solar system, every particle is in 1 of 3 states depending on speed. 1 Falling into the sun, 2 orbiting the sun, or 3 leaving the solar system. state 1 and 3 clear up fairly quickly leaving just particles already orbiting. These use gravity to form larger planets with the same orbit as the particles that made it up (on average).
so its random chance the orbits are what they are, but planets being in some orbit is basically guarenteed when a solar system is formed
Random chance does indeed play heavily into planetary system formation. It is basically survivor bias where we only see the material that randomly ended up in a stable orbit but can not see the huge amount of material which were either flung into the Sun or out into far space. Any planetoid which was not in a stable circular orbit would likely end up crashing with another object changing its orbit or at least get pulled out of orbit by these other objects.
As in, planets orbiting around the sun? Mostly they started with that much energy, the stuff that wasn’t in the range of velocities compatible with orbiting either fell into the sun or flew off into interstellar space. The rest coalesced into planets in roughly the same orbits as the original material, occasionally colliding with other stuff.
Gravity speeds you up as you get closer to a massive object, and slows you down as you get farther away. An eccentric orbit has you moving slower at the high point of your orbit than a circular orbit at that altitude, and faster at the low point of your orbit than a circular orbit at *that* altitude.
To get from Earth’s surface to low earth orbit, you need enough fuel to change your velocity by about 9km/s. Most of that is spent accelerating you sideways, the rest is spent on gravitational potential energy, gravity losses, aerodynamic losses, and steering losses. Once you get to low earth orbit, you need to go about 3km/s faster to escape Earth’s gravity well into a solar orbit.
The “exact speed” in a circular orbit assuming the orbiter is significantly lighter than the object it is orbiting around, is simply solved by a trivial equation:
a = v^2/r = GM/r^2
=> v = sqrt(GM/r)
Where v is orbital velocity, G the gravitational constant, r the orbit radius and M the mass of the object being orbited. So for every orbital speed, there is an orbit radius r where it is stable. Essentially what happens when an object is set into orbit is that as it passed near the other object, if it’s going slow enough, the other object’s gravity will “capture” it and set it into a proper orbit fitting its speed. If it’s too fast, it will escape instead and not be set in an orbit.
In most cases of course, the orbits are not neatly circular, but elliptical, because not every object conveniently comes in at such an angle and speed that they fit into the neat circular orbit. However, there is also a set of elliptic orbits which any captured object can get caught in. Unlike the circular orbit, an elliptical orbit does not have a constant speed, but the speed of the orbiter will vary depending on where on the path it is. But I’ll leave the math for that as an exercise for the reader, as it doesn’t fit into ELI5 and they essentially work the same as circular orbits, since circular is just an edge case of elliptic.
Also, many of the classic nicely orbiting objects (planets around the star, moons around the planet), the object does not “enter” the orbit, but it is formed in orbit from dust that is already orbiting at on average the right speed for that orbit. That’s why these orbits are much cleaner than, say, comets’ orbits.
TL;DR: The objects come in at whatever speed they like, and end up in an orbit that matches their speed, not the other way around.
>if it’s going slow enough
Might want to clarify if it is slowed down enough to be going slow enough.
Planets from from the proto planetary disc, the equivalent to the rings around Jupiter so they are already in orbit when they clump together to form a planet. https://youtu.be/Yhtr2hbg9Rs
Assume a small object passing a much larger one in space. When it passes, the larger object’s gravity pulls at the smaller object, trying to drag it down to the surface.
If the smaller object is going too slow to be in an orbit, it falls inward. As it falls, it gains velocity. If it gains enough velocity, it reaches a high enough speed and it is in orbit. If it doesn’t, it falls all the way down onto the larger object.
If the smaller object is going too fast, It flies outward. As it does gravity slows it. If gravity slows it enough, it enters orbit. If gravity doesn’t slow it enough, its velocity is greater than escape velocity and it flies away into space.
So, when it comes to small objects orbiting larger objects, they adjust their speed to enter orbit, fall all the way to the surface, or fly into space.
Looping orbits are ellipses. Circles are just one very specific exact type of ellipse. (And if you measure precisely enough you can always find enough variation to make an orbit not count as absolutely circular).
And the reason this matters is that while there *is* an exact speed needed to be in a *circular* orbit, there isn’t an exact speed needed to be in some other type of elliptical orbit. There’s a wide band of speeds that work.
The consequence of your speed being “not quite right” isn’t “you fall down”. The consequence is “your elliptical orbit is more elongated, farther from being circular”.
It’s only when that ellipse is skinny enough that part of it touches the planet (or planet’s atmosphere) that the orbit will fail and you’ll crash.
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