Earthed

How would habitability be different if alien planet orbits around red dwarf rather than yellow star?

It's possible that plants and animals can develop on planets (like Earth) that orbit around yellow star like the sun, and at just the right temperature.



Would it be possible for plant life and fish creatures to develop on a planet that orbits around red dwarf?

Public Comments

1. Considering that red dwarf stars outnumber yellow main sequence stars by about ten to one, it would seem unlikely that we would find ourselves with a yellow main sequence star for a Sun based on sheer statistics.
   
   
   
   That implies that there is a non-random selection mechanism that caused our sun to be a yellow main sequence star rather than a red dwarf.
   
   
   
   Or to put it another way, there is some property about red dwarfs and their planets that makes them an unlikely abode for life compared to yellow main sequence stars.
   
   
   
   At this stage one can only speculate as to the cause. I'd suggest that probably Earth like planets do not readily form in the habitable zone of such stars, or their solar systems are unstable over periods of a billion years. I'm sure there are other possibilities.
   
   
   
   I would not say that an inhabitable planet is impossible, just less than ten times likely than for a yellow main sequence star.
2. A red dwarf would have a smaller region where water is liquid, which by current thinking means the odds are lower for a habitable planet. Also, research and analysis of the nearly 300 extrasolar planets so far discovered suggests red dwarfs have fewer planets than other stellar types, for as yet not understood reasons.
3. Life could evolve in any environment, so life could certainly evolve on a planet around a red dwarf star.
   
   
   
   Life on that planet would have evolved to lower light levels, less heat, and less ultraviolet light.
   
   So the plants might not use chlorophyll for photosynthesis, and so may not appear green.
   
   And depending on abundance and temperature, animal life may be very different than on Earth - if there is no liquid water you wouldn't have fish equivalent lifeforms.
   
   And if the air was very thin, you might not have bird equivalent lifeforms.
4. Stars having mass less than 0.8 suns will torque the rotation of planets in their liquid water zones to integer ratio tidal lock within three billion years. A red dwarf has a mass less than 0.3 suns, so the planets in their liquid water zones are surely tidally locked. A 1:1 tidal lock, in which the planet keeps the same face always toward the star, is a condition adverse to the evolution of life. But a 2:3 tidal lock, in which opposite sides of the planet face the star on successive periastrons, might be okay.
   
   
   
   Another problem with habitable planets near red dwarf stars is that red dwarfs flare about as brightly as our sun does. However, a flare on a red dwarf can temporarily make a significant increase the total luminosity, and the higher levels of radiation during flares would probably be bad for life on the red dwarf's planet.