Tidal locking for planets of K type (orange) dwarf stars

In summary, a K-type star has a smaller chance of dangerous flares than M-type stars, and is more likely to have a habitable zone that is farther out. This is why tidal locking is of interest to astronomers studying exoplanets.
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Hello.

If its possible I'd like to find out more about tidal locking for planets orbiting K type dwarf stars.

Specifically, at what distances from their host stars would exoplanets have to be to avoid becoming tidally locked. I'm specifying K dwarves because, from what I've read (see below), they appear to have two big advantages over M type red dwarf stars. Firstly, K dwarves appear to have a smaller likelihood of dangerous flares than M dwarves. Secondly, because their habitable zones are further out than that of M dwarves. This latter advantage is why I'm asking about tidal locking.

If I can understand more about tidal locking I can then 'plug' this into the findings of satellites like Kepler, Tess and Gaia.

This Wiki page gives a reasonable summary of the benefits of K dwarves, when it comes to the possibility of life-friendly exoplanets.

https://en.wikipedia.org/wiki/K-type_main-sequence_star

Thank you.

Cerenkov.
 
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  • #2
Here's the Wiki article on Tidal locking
https://en.wikipedia.org/wiki/Tidal_locking
It has a formula for estimating the time scale for achieving tidal lock.
The time decreases by the square of the mass of the Star
And increases by the orbital radius to the power of 6
The mass- luminosity ratio for a K class star has the luminosity increase by the mass to the power of 4.

So you'd need to start with a base mass ( in solar masses) for the Star. From that, estimate its luminosity and thus the distance of it habitable zone from the star. And with the mass of the star and the orbital distance you'd could get a ball park figure for the timescale over which tidal locking would occur, and how that compares to the age of the planet.
 
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  • #3
Thanks Janus. That's great!

I'll visit that Wiki page, look at the formula and then see about applying it to some Kepler or Tess data sets.

Thanks again.

Cerenkov.
 
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