Turn, turn, turn

[james_davis_nicoll]

I am not great at concisely explaining why it is solar tidal forces and an eccentric orbit allowed Mercury to avoid Lunar-stye 1/1 tide-locking in favour of a 2/3 spin-orbit resonance. Oh, well. First world problems.

Comments

[beamjockey.livejournal.com]

Try your hand at explaining quantum computing to a reporter in two sentences.

[austin-dern.livejournal.com]

I see what you did there.

[w. dow rieder (from livejournal.com)]

Since no one lives on Mercury, or plans to anytime soon, this is only a difficulty for discussions on Earth.

So it's a Third world problem. Which can be safely ignored.

[maruad.livejournal.com]

Thank you for giving me my first smile of the day.

[voidampersand.livejournal.com]

Actually there are many good mathemeticians in the third world.

[neowolf2.livejournal.com]

I'm not sure there IS a simple explanation for the 3:2 resonance of Mercury.

[del-c.livejournal.com]

Spin and angular motion around the sun are synchronised due to tides, and tides are much more powerful close to the sun than further away (third power or higher). So the main thing that is being synchronised is the spin and the angular motion at perihelion, not the mean angular motion throughout the orbit.

Mercury has an orbital eccentricity of 0.2 and a 3:2 resonance. It would probably have been 1:1 synchronised if it were in a circular orbit, maybe 7:5 if the eccentricity were 0.167, or 5:3 at eccentricity 0.25.

There may be a reverse effect as well, orbital eccentricity driven by spin-orbit resonance. We could check to see if the orbits of extrasolar planets are clustered around certain values.