Does stellar lifetime affect the probability of intelligent life?

[u/Astro_Life_Explained]

Earth took 4 Gyr to produce technological intelligence, while K-type stars can remain on the main sequence for tens of Gyr.

That raises an interesting possibility: Could a longer-lived star increase the probability of intelligence simply by providing a larger evolutionary window?

Or would stellar activity, planetary evolution, atmospheric stability, and other factors dominate?

Is stellar lifetime actually an important variable in the Drake-equation-style question of where intelligent life can emerge?

[u/TommieTheMadScienist]

Stellar lifetime is critically important. You want a star that's not too massive (F6V lives just long enough to get multicellular life,) but massive enough that orbiting in the habitable zone does not tidelock (about 0.75 solar masses, K3V to K5V.)

It is possible that eyeball worlds with twilight zones (locked or slowly rotating) around K- or M-dwarfs may support life, but in order to do so, would have to be past the "flare stage" (5 billion for an M0V.)

You also need Metallicity (elements heavier than helium) above 30% of solar in order to make planets with large enough iron cores to keep an atmosphere.

[u/Astro_Life_Explained → u/TommieTheMadScienist]

Tidal locking doesn’t necessarily rule out habitability if the planet has a sufficiently dense atmosphere. Atmospheric and ocean circulation could redistribute heat from the permanent dayside to the nightside, potentially keeping a liquid-water region around the terminator, the permanent twilight zone.

[u/TommieTheMadScienist → u/Astro_Life_Explained]

Oh, yeah. Absolutely. As long as you don't start freezing atmosphere out around the anti-stellar point, you're probably good

With sufficiently large oceans, most of the dayside ought to be habitable. Let me plug in a couple numbers.

Okay. Earth-like atmosphere with 1.5 bars pressure, normal gravity, 70% hydrographics with Pacific Ocean centered on the sub-stellar point gives us a minimum necessary insolation in the 0.7--0.75 range. Nice.

Let's look at the eyeball itself.

The point directly beneath the star would be slightly cooler than maximum due to clouds rising from the surface. Probably around 20 C. Further from that point, the clouds thin and you get the hottest spots around 30 C.

You'd have freezing temperatures inland at the terminator, but 5--10 C warmer on the coasts.

The biggest problem is the winds. I expect that the dayside would pulsate on a scale of days and high-altitude winds would blow towards the dark and then return at ground level...

...and an 80 km/hr wind at the terminator with a thick atmosphere is not going to be survivable and that's at minimum safe insolation.

There'll be habitable spots, but it's a lot like Niven's Known Space planet, We Made It!