this post was submitted on 21 Dec 2023
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Science Memes

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uncomfortable levels of eye contact (mander.xyz)
submitted 11 months ago by [email protected] to c/[email protected]
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[–] [email protected] 32 points 11 months ago* (last edited 11 months ago) (2 children)

Yeah, Earth's moon isn't the only satellite to tidally lock to its planet. In fact, several are.

Photos and Deimos are tidally locked to Mars. 8 of Jupiter's moons and 15 of Saturn's. Pluto and Charon.

Mercury is tidally locked to the sun, but it's in 3:2 resonance rather than 1:1.

[–] [email protected] 16 points 11 months ago

Now those are some fun facts.

[–] [email protected] 11 points 11 months ago (2 children)

Can you ELI5 that last one?

[–] [email protected] 5 points 11 months ago (1 children)

Mercury orbits the sun every 88 earth days. It spins on its axis every 59 earth days, relative to an outside observer (sidereal day.) That makes the solar day (from sunrise to sunrise) 179 earth days long.

[–] [email protected] 2 points 11 months ago (1 children)

So in a certain sense, a 'day' on Mercury is 2.034090909090 'years' long? (Solar day divided by orbiting the sun, lol)

[–] [email protected] 5 points 11 months ago* (last edited 11 months ago) (1 children)

No. I rounded off the numbers. A Mercury day is exactly 2 Mercury years. Which is why it's "in resonance". That means that gravity will speed up or slow down the rotation to keep the ratio stable over time.

[–] [email protected] 2 points 11 months ago

Oh that's really neat!

[–] [email protected] 2 points 11 months ago

Guys please upvote we all need an eli5