Is there a distance at which a satellite will orbit a body indefinitely? Is this distance a universal constant?
As I understand it, satellite bodies are generally getting closer or further away from the body they orbit. Our moon, for example, is getting further away.
This morning I was reading a great essay
by Amy Leach
in the Best American Essays 2009.
In the second paragraph, it is noted that unless you [a satellite] happen to roll onto a track precisely 18,254 miles above your planet, the law ejects you or dashes you down. One moon in our solar system has achieved synchronous orbit, being pledged forever to its planet--Pluto's moon Charon. The other 168 moons have not.
According to google, 18,154 miles = 29,216 kilometers
The wikipedia article about Charon
cites a distance of 17,536 ± 4 km to system barycenter, 19,571 ± 4 km to the center of Pluto
. The radius of Pluto is, apparently, 1,153 ± 10 km. 19,571-1,153=18,418, which is close to 18,254 (though not 'precisely'), but nowhere near 29,216.
Am I missing something obvious (I'm not very good at space, so I am pretty sure this must be the case) or is Leach using poetic license, or is it a bit of both?
I find it hard to believe that there would be a universal perfect orbit distance, as celestial bodies are of varying mass, and there are also external tidal forces acting on them. However, I also find it hard to believe that there are big balls of rock and ice in mutual orbit, and that these systems are, themselves, in orbit around a huge ball of gas.