Red Dwarf Star Systems -- Could they support life?

[Lren Zvsm]

This is a question for people who know about astrophysics. It's been said that the habitable zones around red dwarf stars are so close to those stars that any planets in the zones would be tidally locked to the stars in question. With one side roasting and another side freezing almost forever, those planets wouldn't be hospitable to life.

a) Could there be forms of life--whole ecologies--that first evolve in the planet's twilight zone and then extend their habitat by burrowing underground where the temperatures would be more even on both sides of the planet?

b) Could the planets in question orbit gas giants, allowing for day and night even in the red star's habitable zones?

c) Could double planets, like the Earth/Moon system, eclipse one other often enough to allow the temperature to alternate at least on one side of the planet?

d) Could planets orbiting red dwarfs, tidally locked though they may be, be colonized cybernetic beings, which could be made of a broader range of materials than biological organisms, which would generally be made of more temperature-sensitive materials like proteins and lipids?

e) Could binary red-dwarf systems contain planets that experience day and night?

 

[phyzguy]

This is a question for people who know about astrophysics. It's been said that the habitable zones around red dwarf stars are so close to those stars that any planets in the zones would be tidally locked to the stars in question. With one side roasting and another side freezing almost forever, those planets wouldn't be hospitable to life.

I've never understood why people say this. Depending how far the planet is from the red dwarf star, the temperature on the side facing the star could be perfectly hospitable. Why does it have to "roasting"? I could imagine life that evolved on such a planet saying, "A planet like Earth is inhospitable to life, because there are periods of darkness and we know life is dependent on light."

 

[GTOM]

I've never understood why people say this. Depending how far the planet is from the red dwarf star, the temperature on the side facing the star could be perfectly hospitable. Why does it have to "roasting"? I could imagine life that evolved on such a planet saying, "A planet like Earth is inhospitable to life, because there are periods of darkness and we know life is dependent on light."

isnt it an issue, that solar flares are deadly so close to the star?

 

[Hornbein]

isnt it an issue, that solar flares are deadly so close to the star?

I dunno, how inclined are red dwarfs to solar flares?

 

[phinds]

I dunno, how inclined are red dwarfs to solar flares?

very, apparently. Google is your friend.

 

[phyzguy]

There are a lot of red dwarfs out there, and they live for a very long time. The flares tend to decrease as the stars age. Given the probably hundreds of billions of red dwarfs out there in our galaxy, I don't think you can categorically write them off by saying, "Planets around red dwarf stars can't be habitable because of flares."

 

[Bandersnatch]

Late to the party, but I can offer some intuitions.

a)...e)

Re.: a&d, these are not questions about physics, but alien biology and technological capabilities. The space of possibilities here is so large that it's impossible at this time to decide what is and isn't possible.

Re.: b&c, these are essentially the same question, with the same answer - the same tidal interactions that lock the planet to the star destabilise any multiple system you can imagine there. Whether it's moon or moons, or the planet being a moon of a gas giant, or 'double planet' - the presence of the tidal influence from the star strong enough to lock the planet in synchronous rotation precludes any long-term stability of such systems, as it also acts to eject the superfluous elements.
If you were to encounter such a system, it'd mean it was recently formed, which in turn makes it hard to imagine the formation of a stable biosphere.

Re.: e, you can have a stable configuration with the red dwarf and its planet orbiting a much more massive, brighter star on a wide orbit, so that the 'year' of the planet bringing it around the dwarf causes the brighter star to illuminate different parts of the planet. The 'day' in this case is roughly the length of the planet's orbit around the red dwarf. The planet would have to be further out from its host star to account for the extra energy received.

 

[Bandersnatch]

I've never understood why people say this. Depending how far the planet is from the red dwarf star, the temperature on the side facing the star could be perfectly hospitable. Why does it have to "roasting"? I could imagine life that evolved on such a planet saying, "A planet like Earth is inhospitable to life, because there are periods of darkness and we know life is dependent on light."

The argument here is that without rotation there could be sufficient difference in temperature between the two sides to either boil off water on the illuminated side, or freeze it on the far side. The issue with freezing here is that provided it's cold enough to freeze any water - all water will eventually end up frozen. I suppose boiling off would be less of a problem, but perhaps atmosphere loss in this case could be an issue.

However, I remember reading a paper attempting to model heat transfer via ocean currents, concluding that at least a global ocean is sufficient to keep water liquid on both sides. The question then would be how much land could one add before the heat transfer becomes too inefficient.
Other papers I remember tried to model cloud cover on the illuminated side and address that flaring issue. The general vibe I took from those was that - once modelled in a more comprehensive fashion - the problems with habitability prove to be less severe than the first-look, naive considerations would suggest.

I could try digging up what I read if requested, but it was years ago now, so a more informative approach for the interested would probably be to search articles on arxiv for key words including red dwarf and habitability.