Habitable Planet around Red Dwarf

Question

Is there the possibility for a habitable Planet around a red dwarf? It is not required that the whole surface is habitable, but it shouldn't be a tiny spot.

After reading a bit I assume the planet would be tidally locked to the star, with the side that faces the sun looking like an archery-target (from center to border: scorching, hot, warm, cold, freezing).

Also from space it would look like a Rugby Ball (exaggerated) pointed at the star.

But would such a planet be stable enough to develop and support life more complex than the simplest forms?

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I do not need a specific star, but the general answer if this is possible, however unlikely (though a value how unlikely would be nice).

Answer 1

Well, it's a relatively new field of study so I don't think there's any exact answers, but I've read up on this a bit out of interest. Red Dwarfs have 2 main disadvantages. One, which you've mentioned. They're relatively cold compared to our star so the planet would need to be comparatively close and therefor, probobly tidally locked. The other problem is red dwarfs tend to have very active sunspots compared to our sun, so the planet would need a crazy strong magnetic field to protect the planet. Neither of those are "deal breakers" but perhaps less likely than a sun-like star.

A tidally locked planet wouldn't necessarily have a scorching hot side and a freezing cold side. Modeling suggests that temperature would circulate. If it had extensive oceans on the tidally locked side, for example, that could create a cloud cover and not cause intense heat. You could also have the sun side be far enough away to be temperate and the star-side icy, or a livable section in a ring around the planet.

There's also the possibility that a tidally locked planet could have winds that we would find very difficult to adapt to.

I think you'd ideally have the sun side be the habitable side for photosynthesis.

On the flip side, if the star is too large, the star's life would probobly be too short for the planet to cool down enough to be habitable for us. The life of a star is the inverse cube of the size, so a star twice the size of our sun would only have a main sequence of 1.2-1.3 billion years. When you get a bit bigger than that, there's not enough time for a planet to cool off and a solar system to get past it's heavy bombardment period.

So I'd give a red dwarf a better chance of having a habitable planet than a sun 2.5 times or larger than our sun. That, and red-dwarfs are the most common stars in the galaxy, so I think there's a probability that some red dwarfs could have habitable planets.

Answer 2

Gliese 581 is a red dwarf with several planets. The planet Gliese 581 c was in fact the first roughly Earth Sized planet ever discovered in the habitable zone around another star. Currently, it looks like it probably is very hot because of extreme Greenhouse effect similar to Venus. But that's already pretty good. Gliese 581 is not a particularly big red dwarf, there are some that have almost twice the mass and their habitable zone would be farther out, making the whole system a bit more similar to ours.

Since red dwarves are small and live extremely long, they are actually considered pretty good candidates, since conditions on orbiting planets would be pretty stable over very long amount of time, without the sun changing its behavior.