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Old Jun 2 2015, 06:06 PM   #4
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Default Re: The Size of Pern

Originally Posted by Kath View Post
Acceleration due to gravity is: g = G M / r^2

Putting the numbers in - g=0.9*9.81, G=6.67e-11, r=5.2e6 - gives a mass of 3.6e24 kg or 60% of the Earth's mass. In terms of density, Pern has a density of 60%*(6.3/5.2)^3=107% of Earth's average density.

Timor having a size comparable to our own moon is, if you'll excuse the pun, improbable lunacy! Planet formation doesn't lend itself to massive moons, but if we do let Anne get away with it, then Pern must have had some major planetary trauma in the past. That could also explain its higher density - much like Mercury, it could have a larger than expected iron core and a smaller mantle following a moon-making collision.
That sounds plausible enough when explained that way. Scientists have found weirder things out in space so far.

Originally Posted by Kath View Post
No comment on eclipses, except that they're very unlikely to be total.
What makes you say that? Would having two moons make that much of a difference?
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