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View Full Version : Tidally Locked Planets?

2007-Sep-11, 06:14 AM
Hello all,

I recently read up on what Tidally locked planets were - from my understanding it was when the planet has one side permanently facing its parent star.

I was wondering if there was a way to determine if a planet was tidally locked or not, just with the data of the planet and sun. Basically I have a random generator that generates a star and then planets - is there some way/equation I can use that will determine if planet "A" is tidally locked or not?

Part two of the question (I combined them as I didn't want to "spam" the forums ;) )
How can I determine the maximum mass of a moon that the planet can theoretically have?

Thanks,

tusenfem
2007-Sep-11, 08:04 AM
Well, I am not sure how your generator works, but take the generated planets' orbital times and take the generated planets' rotation time. If for any of the planets the two are equal (both in value and sign) you will have a "tidally locked" planet. Although more accurately you have a planet with the same face to its sun at all times, whether it is because of tidal workings is another question, because everything is created by a random generator.

About the maximum mass of a moon? I would say the maximum would be the planet's mass, as when the moon gets more mass, the roles will be reversed.

EDG
2007-Sep-11, 08:29 AM
I was wondering if there was a way to determine if a planet was tidally locked or not, just with the data of the planet and sun. Basically I have a random generator that generates a star and then planets - is there some way/equation I can use that will determine if planet "A" is tidally locked or not?

The short answer is "Yes, but it is REALLY complicated." Generally speaking, most planets within about 0.7 AU of a star will tend to be tidelocked or in some wierd spin/orbit resonance (like Venus or Mercury) after a few billion years - the closer they are the faster they tidelock (planets in the habitable zones of M V stars tidelock REALLY quickly, since they're usually less than 0.2 AU from the star). Also, smaller planets take longer to tidelock to a star than larger ones, and gas giants in close orbits take a really long time since they're made of gas rather than rock (which means that their tidal dissipation factor (Q) is a lot higher than a rocky planet).

2007-Sep-11, 08:56 AM
My generator at the moment only calculates mass, radius, density, escape velocity, etc. No orbits at the moment, but I plan to do them if it is not too hard. If it isn't, how would I go about calculating an orbit of a planet?(knowing the Sun's data and the distance from planet to sun) ;)

Thanks ;)

Tobin Dax
2007-Sep-11, 01:27 PM
P^2 = 4*pi^2*a^3/(G(M+m))

P = orbital period