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Princeofcatpoop t1_j4yrv7c wrote

There is actually a science fiction book about just such a pair. One is a water world and the other dry. The human explorers arrive just as the water is about to switch planets in a once a millennium event. Fun read. I think it was Rocheworld? I think I only read the second one of the series.

There is also an animated movie featuring this concept voiced by kirsten Dunst called Kaena: the Prophecy. And the movie Upside Down, also starring Kirsten Dunst, that has some ideas on the socio-economic repercussions of such a setup.

Ultimately the math probably doesn't work out for any of these concepts without some fantasy style materials being involved. In order for two planets to be close enough to share an atmosphere would require orbits of such extremes that it would rip the planets apart.

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Princeofcatpoop t1_j4ysk1a wrote

Tidal locking happens when extreme gravity differences cause the objects to slow down. The steeper the gravity quotient, the faster the tudal locking occurs. The moon is relatively small compared to the Earth so it stopped first (relatively) but as it recedes, the earth slows too. Meaning our days are getting longer. By about .25 seconds per century.

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the_fungible_man t1_j4yu3v2 wrote

>By about .25 seconds per century.

By about 0.002 seconds per century.

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