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Worldbuilding

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  • $\begingroup$ Phobos completes an orbit in about seven and a half hours, and traverses the Martian sky in "4 hours and 15 minutes or less" (west to east, of course). The International Space Station, which is sufficiently large to be quite often visible with the naked eye (and could easily be much larger), completes an orbit in about an hour and a half; but because of its low altitude needs to be boosted periodically. What answer does the question expect which is not already provided in the usual places? $\endgroup$
    – AlexP
    Commented Dec 9, 2022 at 13:13
  • $\begingroup$ @Igysin Habitable Planets for Man, 1964, Stephen H. Dole, discusses the limits of how fast or slow a planet habitable for humans could rotate. rand.org/content/dam/rand/pubs/commercial_books/2007/… For a completely airless planet, the orbital period of a satellite at the surface is the shortest possible orbital period, but for any planet & moon combination, the Roche Limit of how close that moon can get before breaking up can be calculated. I note that even thousand of miles above the surface of Mars, there is enough air to lower the orbit of Phobos. $\endgroup$
    – M. A. Golding
    Commented Dec 9, 2022 at 18:07