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Message: <blockquote data-quote="Umbran" data-source="post: 5357088" data-attributes="member: 177">Well, the moon has to be smaller than the planet.  Other than that, I can only speak to vague probabilities.Given what I know of the detection methods, any moon of 581g would not just be smaller than the planet, but much, much smaller.  They found 581g using "radial velocity" measurements - basically, looking for tiny wiggles in the star's movements.  We know the mass of 581g from that wiggle - and that mass is actually the total mass of whatever is orbiting there, planet and moon combined.581g is supposedly about 3x the mass of Earth.  Let's say that it was more like a planet of 2x, and a moon the size of earth.  Those are both still big things, and the two of them whirling around in that orbit would be different than a single large planet, in ways I think (educated guess there) would be detectable.So, expect any moon to be more like Phobos or Deimos is to Mars, than our Moon is to Earth.  But that's just a guess.If the planet is tidally locked, any moon is probably in a resonant orbit, yes.The minimum orbital distance is a mostly unrelated issue - if the moon is large, there's a minimum distance it could be from the planet.  Closer than that and it'd probably get torn apart by tidal forces. If the planet's wobbling more than a little bit, it isn't really tidally locked yet.Okay, you're talking about a star, a planet, and a moon - which orbit are you talking about?Tidally locked orbits tend to be nearly circular.  Orbits with other resonances may be significantly more eccentric.</blockquote>

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