Celestia Forums

Hi all...

Is there a particular distance from a star that a planet *will* become tide locked to that star? For most of my add-ons, this isn't really a problem, since with G-types or F-types, a habitable planet won't run into those issues, while a M-type star, the planet will almost certainly be tide locked.

But with K-type stars, the HZ zones can vary quite a bit, leading to my current problem of determining rotational rates.

Thanks, and a happy New Year to you all!

...John...

Generally, if the planet is within about 0.5 AU from any star, it's very likely to be tidelocked. Though you can get odd 3:2 resonance situations sometimes as with Mercury, but I think that's more down to the eccentric orbit.

Thanks!

One brief follow up question, though, that had forgotten about. How long does it take for tide locking to occur? Will I have a tide locked world in a system 1 billion years old? Three? 500 million years old?

...John...

Depends on the mass of the star and a whole load of planetary geophysical properties. Gas giants take a VERY long time to tidelock, if at all. (unless they're hugging the corona, in which case it takes shorter). But in some terrestrial cases you can get a complete spindown to tidelocking in only a few million years. Heck, it may be that for satellite systems around gas giants they could even FORM already tidelocked because of the effects of the primary on them as they coalesce out of the disk around the planet.

In other words, it depends on a lot of things.

Gotcha. So I'll probably just make some assumptions based on age and mass, etc. I don't think many folks can begrudge me that amount of fudging... **chuckles**

Thanks again!

...John...