# planet question

**URL:** <https://boards.straightdope.com/t/planet-question/145477>\
**Category:** Factual Questions\
**Created:** [December 29, 2002, 6:04am UTC](https://boards.straightdope.com/t/planet-question/145477 "2002-12-29T06:04:24Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![raisinbread](https://avatars.discourse-cdn.com/v4/letter/r/8491ac/32.png) [@raisinbread](https://boards.straightdope.com/u/raisinbread)\
**Post date:** [December 29, 2002, 6:04am UTC](https://boards.straightdope.com/t/planet-question/145477/1 "2002-12-29T06:04:24Z")

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I was going around on the web and found a site that creates a solar system. One of the things it listed was “planet’s rotation is in a resonant spin lock with the star.”

What the heck does that mean? How does it differ from being tidally locked?

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**Author:** ![MEBuckner](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mebuckner/32/2896_2.png) [@MEBuckner](https://boards.straightdope.com/u/MEBuckner)\
**Post date:** [December 29, 2002, 6:09am UTC](https://boards.straightdope.com/t/planet-question/145477/2 "2002-12-29T06:09:24Z")

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I think they mean that the planet would have a day/year relation that would be something like that of Mercury’s. It was long thought that Mercury was tidally locked–that its day and year were in a 1:1 ratio–but back in the 1960’s it was discovered that the ratio is actually 3:2–Mercury rotates on its axis three times for every two times it orbits the Sun.

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**Author:** ![bryanmcc](https://avatars.discourse-cdn.com/v4/letter/b/eada6e/32.png) [@bryanmcc](https://boards.straightdope.com/u/bryanmcc)\
**Post date:** [December 30, 2002, 9:26pm UTC](https://boards.straightdope.com/t/planet-question/145477/3 "2002-12-30T21:26:39Z")

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How about a link to this cool-sounding site?

By the way, I concur with **MEBuckner**.