Really great feedback guys, thanks for sharing all your thoughts. It's truly helped my system become not only more realistic but more detailed.Originally Posted by Azelor
Actually tidally locked planets rotate, they just rotate at the same rate that they make a revolution. That is why this planet does have a North Pole, just like our moon does. Where it is just depends on axial tilt. Orbit is indeed possible, though I'm sure it would be eccentric. I hadn't considered it too big of a problem... The real problem, I realized, after these theories got me doing more research, is that unless the moon was close enough in mass by a factor of 10 it would either fall into the planet or the sun at some point depending on which orbit was faster (which is in agreement with Raptori's theory except that larger moons actually are more sustainable.) The real problem here is just that a very big moon would probably cause the objects to become tidally locked to one another - a great idea for a different planet project, but alters this one too much.
I figured some kind of collision would have been the reason for the moons, but if they'd be falling into the planet eventually, I'd rather scrap them, however, it seems interesting that two similarly sized objects can be tidally locked to each-other and orbit a sun... I -could- go with my collision idea and say that once there were two worlds orbiting one another, which is a scenario that would give life an earlier chance to get started, too (wider habitable zone from day/night.) Let's say a disaster broke up the sister planet, creating a few moons, either destined to someday coalesce into a large enough object to hold orbit, or eventually fall into the sun. The recent-ness is really not a big issue, since in astrological terms "recent" can give or take hundreds of millions of years. My ancient sentient race is only a tenth of that age. Life could have survived such a bombardment and still be very diverse at present, (Die-offs actually promote evolution, by opening new niches for more and more complex organisms to fill.)
But I digress, if most of the debris was propelled at a trajectory that sent the largest chunks of the sister planet into the sun, leaving smaller bits to shower our host or coalesce back into the biggest remaining chunk of the sister, then it might work out for life. The moon might still be large enough to orbit for a good while if, like Raptori says, it's close enough.
This would cause some strange things to happen, but I think they might be beneficial. The tides would be very aggressive and stir up the sea a bit, good and bad... There might even be a noticeable change in gravity depending on where the moon is at, just fun... I assume the planet would stay locked to the sun but it would wobble distinctly. This would actually help create more dynamic weather, and keep hot spots from being too extreme - the desert in the center might not actually cook flesh off bones. (Otherwise, my world doesn't have a big enough liquid sea to have a lot of ocean current and distribute heat.) The moon would have to be just the right size, though I'm confident that size exists, whether I figure it out or not. In conclusion, it doesn't really matter if the moon will stay in orbit forever, because neither will our own, after all.
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