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Approximately how likely is it that a tidally locked planet would have a long term natural satellite, and where would that satellite most likely be located? What I've so far researched (and puzzled out on my own) indicates it would be extremely unlikely and would either follow the terminator line or be opposite the star and orbiting at such a pace as to be geosynchronous.

Additionally, would it be feasible to place a man-made satellite at such a planet, assuming fuel/spacefaring technology has not progressed too much (I have another explanation for traveling from one system to another) and considering the fuel requirements to keep the satellite in orbit?

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  • $\begingroup$ Could you tell us more about these planets? Are they earth like in size and composition? What is the planet tidally locked to? The star? Another planet? Another satellite? What size would your natural satellite have to be? $\endgroup$
    – Xandar The Zenon
    Commented Mar 10, 2016 at 4:49
  • $\begingroup$ I wanted some "real" solar systems to be integrated into my world and thus began my journey into astronomy. I was first introduced to the idea of a tidally locked planet when researching Zarmina (orbiting Gliese 581). It has no known satellites (it's own existence is disputed). I thought I should include some into my wholesale-created solar systems to make them more realistic. At this point I'm creating solar systems - 19 of them - and just beginning to consider many of the questions you asked. $\endgroup$
    – Angela M Phelps
    Commented Mar 11, 2016 at 14:47
  • $\begingroup$ That is flattering. I like to create solar systems for fun. I'm trying to figure out the best configuration for a story I'm writing. Although I do like this question. $\endgroup$
    – Xandar The Zenon
    Commented Mar 11, 2016 at 14:52

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Yes, but with limitations.

The fact that a planet is tidally locked does not by itself stop it having a moon or a satellite. In fact Mercury was orbited by an artificial satellite called MESSENGER for several years. Mercury may not have conventional tidal locking, but it does have a form of tidal locking called spin-orbit resonance.

However the factors that lead to tidal locking tend to involve a body orbiting close to another body, and often a smaller one around a much larger one. Both of those factors make it much harder for the tidally locked object to have satellites of its own. Artificial satellites stable for a few years would generally be fine but natural ones stable for millions of years would be highly unlikely.

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  • $\begingroup$ That was my thought, that the gravitational pull of the other body would pull any satellite out of orbit. I figured it would influence the placement of man-made satellites. I also thought it would be interesting to have one planet that won the astronomical one-in-a-billion lottery and did have a natural satellite. Maybe it'll be a tourist trap. Where do you think the safest placement would be? The terminator line (where the pull of the other body is relatively constant), opposite the other body (where the pull is lowest) or some other placement? $\endgroup$
    – Angela M Phelps
    Commented Mar 11, 2016 at 15:04
  • $\begingroup$ It's an n-body problem. en.wikipedia.org/wiki/N-body_problem the first thing you need to do is clear out all other moons, that will help. Beyond that...maybe. Essentially you want the gas giant to be as big as possible, the first level moon as far from it as possible, etc. Try something like the universe sandbox program. $\endgroup$
    – Tim B
    Commented Mar 11, 2016 at 15:26
  • $\begingroup$ Thank you for your help. This is my first 'real science' fiction and more often than not I find myself asking the wrong questions. Luckily I enjoy research, or I'd have given up on this idea long ago. "universe sandbox" And there goes my next several months.... $\endgroup$
    – Angela M Phelps
    Commented Mar 11, 2016 at 16:07
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Tides happen on the Earth because of the gravity of the moon is strong enough to shift the seas around . If your natural/artificial satellite is sufficiently small ( which means it will have less gravity ) and sufficiently far away from the planet (but close enough to be in orbit) , then it won't influence the tides of the planet and the planet will continue to be tidally locked .

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