Our Moon orbits the Earth further away each year due to the tidal forces but could there be a moon orbiting a planet where somehow keeps going further away by the tidal forces but its attracted again to the planet (e.g by its gravitational pull) so that this moon's orbit is balanced throughout time not being absolutely thrown out of the orbit nor being excessively drawn onto the planet until it crashes?
$\begingroup$
$\endgroup$
2
-
$\begingroup$ The planet's Hill sphere depends on what's near it. Is this "planet" assumed to still be orbiting a star, or can it be rogue? $\endgroup$– J.G.Commented Apr 3, 2022 at 14:45
-
$\begingroup$ The Earth-Moon distance is changing as energy is released while the angular momentum remains constant. This process may have zero or two “tidally locked” equilibrium distances (though the inner equilibrium is unstable, and a satellite there will either eventually crash into the planet or migrate out towards the outer equilibrium). See this answer of mine for a discussion of Earth’s Moon and Mars’s moons. $\endgroup$– rob ♦Commented Apr 3, 2022 at 15:09
Add a comment
|
1 Answer
$\begingroup$
$\endgroup$
3
"Forever" is a very long time. If you wait long enough, even the Earth will cease to exist, so from that perspective the answer is "no".
On less gargantuan but still exceedingly long timescales, the Moon will radiate gravitational waves and so collide with the Earth. It's the same effect as why two black holes orbiting each other will eventually merge. But the timescale is still longer than the lifetime of the Sun, in which case the Earth and Moon are likely to be destroyed when the Sun becomes a red giant long before they collide.
Suffice to say the Moon will likely orbit the Earth for the next several billion years, by which point things are very difficult to model anyway because of chaos effects. See Wiki.
Edit: perhaps closest to your question is whether tidal forces will cause the moon to recede forever. The answer is no, because eventually the Moon and the Earth will become tidally locked, i.e. you can only see the Moon from one side of the Earth. At that point the Moon will stop receding. See source. The estimated time for this though is ~50 billion years, which is much longer than the expected lifetime of the Sun, so it's all moot anyway.
-
1$\begingroup$ In fact, the Moon is slowly pulling away from Earth, check out en.wikipedia.org/wiki/Moon#Earth%E2%80%93Moon_system: "Measurements from laser reflectors left during the Apollo missions (lunar ranging experiments) have found that the Moon's distance increases by 38 mm (1.5 in) per year" $\endgroup$– jimCommented Apr 3, 2022 at 14:22
-
$\begingroup$ There is apparently evidence to suggest that the Moon was substantially closer in the distant past, having possibly formed as a result of a collsion of two objects that resulted in the Earth-Moon system. See Wikipedia's page on Lunar distance. $\endgroup$ Commented Apr 3, 2022 at 14:37
-
$\begingroup$ @jim yes, but it won't recede forever. $\endgroup$– AllureCommented Apr 3, 2022 at 14:37