What does it mean when matter can no longer stay in orbit? What happens?
In: Planetary Science
Orbits “decay” because there is still a little bit of air around that slows any satelite by producing a little bit of drag.
The higher you go, the less gas there is the longer whatever you have orbits.
So any satelite will slowly lose speed and fall down on earth.
Orbits are not completely stable. If you simplify everything and do the math then the orbit might be stable and last forever but the more things you add the less stable the orbit becomes. For example we assume that space is a perfect vacuum, but it is not. We have atmosphere down here on the surface of the Earth and this atmosphere gets thinner the higher up you go. But the atmosphere never actually disappears, it only gets forever thinner. This means that satellites orbiting Earth is actually getting drag from the atmosphere. It is not much but it can still be significant. And it is used by for example ISS which orbits low enough to be in what is technically the thermosphere, the second highest layer of the atmosphere. There is enough air resistance that they use the solar panels to generate lift just like an airplane wing. By being this low things that orbit near them will get slowed down by the atmosphere and fall down to Earth. The dense space station get less air resistance but still enough that they need to get regular boosts from visiting spacecrafts.
Another issue is that we assume a two body problem when solving orbital mechanics, but this is rarely the case. The Earth and the satellite is not orbiting by itself but there is also the Moon, Sun and Jupiter pulling in every which direction. So even satellites that orbit high up is getting pulled out of place changing its orbit. Over time they might crash into the Earth or fly out into the solar system. The most famous example of this is J002E3 which is an asteroid discovered in 2002 which was discovered to be the upper stage of the Apollo 12 rocket. It was left in high Earth orbit in 1969 but was kicked out of orbit in 1971. Then it got captured again in 2002 and was kicked out again in 2003. It may get captured again in the 2040s.
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