# Althistorybuff

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1. ## Tidal locking in a Red Dwarf System - How would large moon affect?

OK, thanks for the feedback. It sounds like the answer is that very close-in planets around red-dwarf stars would see tidal forces so strong that it would evntually force a large moon to spiral into and crash. Then, the planet eventually would become tidally locked. I appreciated all the help.
2. ## Tidal locking in a Red Dwarf System - How would large moon affect?

Question: I understand that close-in planets in a red-dwarf system are probably tidally locked. However, if the planet had a large moon, would the tidal locking be avoided? Would the tug of the moon keep the planet from being locked? Thanks.
3. ## Early Moon's orbit - Question

So the moon is about 384,000 KM from earth: square root is 619 If it were 10x closer, square root is 195. So roughly, it would be 3.15x faster. Naturally, if we had different masses of each body, that would change a great deal. I looked up IO, which orbits Jupiter at roughly the same distance as the moon does from Earth and it moves 17X faster.

Thanks.
5. ## Early Moon's orbit - Question

Sorry, I'm having trouble figuring out this gravitational/orbital speed equation. G= ? M=Mass of Earth - m= mass of moon? r = radius of the moon to center of earth?

Thanks.
7. ## Early Moon's orbit - Question

From what I gather, the early moon was 4 or so radii away from Earth after formation/the big impact (3 being minimum without tearing apart via gravity and 5 being the maximum the debris would have been spread). Now it is 60 Radii, moving at about 1KM per second. I assume it would have been faster after the Earth/Thea impact. Any idea how much? The main reason for the move was tidal friction from Earths ocean "pushing" forward which transferred momentum to the move and therefore out by about 3CM a year. However, there was is also a theory that the Earth's tilt was up to 60 degrees and that also resulted in an early and quick movement outward by the moon early in its existence. (Matija Cuk) The moon will keep moving out until that angular momentum is transferred to the point where Earth and the Moon are "tidally locked". Presumably, the moon's orbit early in its existence was quicker due to this shorter orbit, though I'm not sure of projected actual speed. Question: If Earth didn't have this "tilt" early on that gravitational interaction with the moon largely corrected (at the expense of the moon making a big and fast leap out), would the "tidal locking" of the earth to the moon have already occurred? If the moon was 15 times closer (I don't know the speed back then so I can't calculate the "month"), would it be possible that the Earth's day/month would have already been "tidally locked" at something closer to what we know as 24 hours? That the moon would orbit so closely that the month would be far closer to what we know as a day than, in the future, our "day" will be closer to what we think of as a month? I know that the Earth rotated faster prior to the impact, maybe 6 hour rotations immediately after (and probably before, I assume). If Earth rotated 24 hours (as we know it) PRIOR to the collision and the moon was much, much closer, and this "tilt" issue wasn't involved, how quickly could the Earth/moon Day/Month be determined. I'm trying to figure out if, after the "Thea" collision, that Earth and the Moon might have found a much earlier, and short, "day/month" combo. Am I missing some large factor? Obviously, the tides would much, much higher/worse and the moon would be far bigger in the night sky. I ran some middle school math. Assuming the moon was formed at 1/10th the current, average distance, this means 2 x 3.14 x 38,500 (actual is 385,000) KM is 241,780 KM. At the current 1.022 KM per second (again, I'm guessing it would be faster back then as the Moon's speed is slower as it moves out), this would mean 65.7154 hour long month? Double the speed and you get pretty close to 33 hour month. If the Earth had been rotating slower back then and the impact maybe slowed it a bit more, would the moon have remained in place at 6 radii?
8. ## Question on Red Dwarf Binary Tidal Locking

Thanks, I think that those were the general ratios I've been hearing. I'm leaning towards the planet orbiting both closely-locked suns. I can't seem to get much response on whether this orbit around two gravitational masses would halt tidal-locking. I've tried a few forums.
9. ## N-Body Problem - need a simple answer for a created planetary system

Ok, I'm trying to get a grasp on the n-body problem as I want an earth-like planet with two large moons of roughly the same size. One scenario is same sized moon twice as far out or a closer moon (Io-type) half the distance between Earth and Luna. Basically, they would NOT be sharing an orbit or Lagrange Point. From what I gather, the Earth isn't massive enough to hold both bodies without them gravitationally pushing one another about too much, at least over medium to long term. I'd like to have this be relatively stable for billions of years. No crashing into the Earth of being expelled. Is this possible? Everything I hear says no, that the system would become unstable sooner rather than later, though I don't know the definition of "sooner" or "later". Even the Sun-Rest of Solar System (500 to 1) or the Jupiter-60 moons System has a level of interaction (thousands to one) gravitationally. Is the idea of a 2nd large moon around Earth not possible? If not, what would be the constraints? I don't need the math, just an idea of how long this would last. Is there a "golden ratio" when the gravity of the large body (Earth) would MOSTLY cancel out the two moons' gravitational effect upon one another? 500 to 1, 1000 to 1? Would creating a certain resonance with their orbits (2 to 1, 3 to 2, whatever) make a difference? Thanks.
10. ## Question on Red Dwarf Binary Tidal Locking

I would assume that the star would outweigh any planet by hundreds of thousands (each star) so I'm not sure if the three body problem would apply.
11. ## Question on Red Dwarf Binary Tidal Locking

Question from an amateur writer: Most planets around Red Dwarf Stars, at least close in, are tidally locked due to proximity. Would this change for planets orbiting a pair of very Close Binary Red Dwarf stars (probably a two or three day mutual orbit)? Since the planet is being dragged by two different suns, often from two different locations when the planet is orbiting from the "side" and can see the suns from two different angles, would the planet be tidally locked is some way? Maybe locked to the common barycenter between the stars? Or would this dual source of gravity allow for the planet to retain its rotation, perhaps even encouraging it? Also, related, do tidally locked planets retain their magnetic fields, at least strong ones, if they don't rotate/spin? Are tidally locked planets potentially difficult to retain life without a strong magnetic field? Thanks.
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