Red Dwarfs

I’ve always found red dwarf stars fascinating. With all the initial focus on the G class sun-like stars in the search for life, the long-lived and numerous red dwarfs seemed to have an enticing promise.

Most of them are too dim to be seen with the naked eye – adding to their mystery. It is estimated that 20 of the 30 closest stars to Earth are red dwarfs, yet no one of them can be seen without a telescope. The closest star to the sun is Proxima Centauri, a red dwarf 4.22 light-years from Earth. Through a telescope you can find it about four full-moon diameters away from Alpha and Beta Centauri, which appear as a single star in the night sky.

Compared to 10-billion-year expiry date suns like our own yellow G-class sun, red dwarfs can have lifetimes up to a trillion years. Am I the only one who is immediately imagining ancient civilisations glistening in the light of their red suns?

One way or another we will end up there anyway. Red dwarfs will outlive every other stellar cousin. If humanity survives that long, our star-faring descendants will have to migrate to nearby red dwarfs to stay in business as our sun fades to a white dwarf and then finally a black dwarf in a few billion years.

Any they do indeed have planets. In 2010 Gliese 581g was discovered around red dwarf Gliese 581 and dubbed the “first potentially habitable planet”. The fifth planet discovered in this system, it is thought to have a period of between 26-39 days and have a mass 2-3 times that of Earth. It’s orbit puts it somewhere similar to where Mercury orbits our sun, but with the lower intensity of the red dwarf, this should still allow liquid water. The Gliese 581 system is also tantalisingly close to Earth – around 20 lightyears away. So the Gliesians might be tuning in to watch 1993 TV on their satellite dishes as we speak.

One potential wrinkle for habitable planets around red dwarfs is the potential for tidally locked planets in close orbits to their suns. In this case, it is theorised that almost all the water would end up frozen on the cooler “dark side” on the planet. If you have enough water, then you would end up with a liquid water ‘ring’ along the temperate zone between the hot and cold sides. Because of the massive pressure of the ice sheets piling up on the cold side, you would get melting underneath, perhaps creating an ocean under the ice that would connect with the vast lakes around the terminator. How it all looks would depend on topography, the temperatures and exactly how much water you had. But somewhere in there would be zones suitable for life.

Anyone else got any fascinating red dwarf facts? Anyone set a story on a world orbiting a red dwarf?

I hope everyone is enjoying their free Calvanni ebook. Stay tuned for a free Scytheman (book 2).

Cross-posted at chrismcmahons blog.

4 comments

  1. I so need to dig up a story I started once!

    I think I got carried away trying to figure out how the Hadley cells might work, and with the much reduced coriolis force, whether you’d get jet stream effects, and then how far toward the sun side irrigation could extend the livable zone, and how far out into the desert of the eternal sun a body would have to be carried to never be found, and would there be cave systems where a captive could be held or someone dumped in the desert to die might find refuge . . . I don’t even remember the story part of the story any more, assuming I even got that far.

    1. Sounds like fun. ‘Where the body cannot be found’ . . . or at least that’s what they think:) So much to play with there. It seems from the background googling I did a lot depends on how much water there is on the planet to begin with, then probably temperature. People talk about ‘eyeball Earths’ the sort of world where you have that desert, surrounded by a ring of water and habitable zone -that kind of looks like an eye.

      Fascinating stuff:)

  2. Hey, a topic I know a little bit about!

    The most recent studies and computer simulations I’ve seen of tide-locked planets suggest that it takes only a very little atmosphere (possibly at little at 0.1 atm) to prevent all the atmosphere from freezing out on the night side, which used to be a major concern. It could still be pretty cold on the night side, but it also might not be if the atmosphere is thick enough or there’s a global ocean current or something else transferring the heat. Venus, after all, has a very slow rotation and doesn’t have major diurnal temperature differences. No one seems to know what causes super-rotation in the upper atmosphere like Venus and Titan have, but a tide locked planet with a year/day more than about 200 hours seems like it might have super-rotation. This might even out diurnal temperature differences even more.

    Hadley cells probably get bigger with slower rotation periods. A tide locked planet might have just two giant Hadley cells. Upper atmosphere wide speeds would also increase with a lower rotation period.

    Some simulations suggest there would be a giant, permanent storm cell in the middle of the daylight side. That could limit the amount of available land. There dark side is resource limited and half or more of the day side is under storm clouds all the time. So the only land suitable for life is around the edges of the storm.

    There are some reasons to suspect M stars aren’t the best stars for life. Many, perhaps most, are flare stars. Others may have giant “sunspots” that take up much of the surface and temporarily dim the stars significantly. And since habitable planets would be much closer to the star, they might be more affected by coronal mass ejections, etc.

    Here is a general, almost readable, paper speculating on the atmospheres of exoplanets:
    http://arxiv.org/abs/0911.3170

    And speaking of Gliese 581g:
    http://arxiv.org/abs/1010.4719

  3. About red dwarfs.

    Most of their light is in the infrared part of the specturm and they don’t emit much ultraviolet. Be hard to get a good tan on a red dwarf planet.

    Any naturally occuring animals would probable see in infrared. Also the chemical composition of clorophile in plants would have to adapt to the light. I don’t know enought chemistry or biology to know how that works. Some things I have read suggested the plants on a red dwarf planet would look black to human eyes.

    Planets tidally locked to their local sun probable don’t have any moons. Or if the planet of a red dwarf does have moons, the orbiting moon could break the tidal lock of the sun on the planet leading to strange day, night, month and year cycles for the planet and moon.

    Early generation red dwarfs and their planets would be poor in metals and be composed of mostly hydrogen. Later generations of red dwarfs that originated at the same time as the sun would have similar composition of metals.

    Those early generation of red dwarfs are still around and will be burning for about a trillion years. They haven’t yet completed going through the main sequence of the stellar life cycle.

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