Talk:Habitability of red dwarf systems
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Some of these comments may be hard to translate into edits permitted by Wikipedia policy, but I should say that the model described in this article seems very limited.
First, as postulated in Isaac Asimov's book "Nemesis", you could have a large planet orbiting a red dwarf with a moon tidally locked to it, which might then have a cycle of day and night.
Also, good things come to those who wait (a really, really long time). See blue dwarf (red dwarf stage)...
Last but not least, there's no theoretical reason why low-frequency light can't be used for photosynthesis. Sure, each photon carries less energy and life would need to evolve a less intense reaction to catalyze in immediate response. But bear in mind that even our own Earth life effectively sums up two photons through a series of milder intermediate reactions. There's no reason why it couldn't use three or four in molecular semiconductors with appropriately spaced band intervals triggering appropriate redox cascades to accomplish the same reaction - nor is it sure that another planet would need the same reaction.
Bear in mind that "infrared light" is not simply "heat", as witnessed by the countless near-infrared camera shots of police and military actions on television. So long as a receiver is not as hot as the surface of the star that illuminates it, it will not emit as much infrared light from its surface as it receives, and it can catalyze a useful collection of energy. Wnt (talk) 03:02, 26 June 2008 (UTC)
- I think it is important that the light have shorter wavelength than the temperature of the environment the life is immersed in, as otherwise the thermal radiation from the environment would probably cause trouble (eg, make reactions go in the wrong direction, etc). I'm pretty sure life cannot arise in an environment strictly in thermal equilibrium, in particular. But there can be chemical sources of energy, and probably others. But I believe there has to be free energy (Gibbs free energy, that is, technically) for anything to happen. Wwheaton (talk) 07:13, 20 February 2009 (UTC)
Proxima Centauri at age=4.85 × 109 is a very active flare star. Barnard's Star is still a flare star despite being a very old star. Flares on Barnard's star are rare. The text is unclear how violent these flares are.—Preceding unsigned comment added by Proxima Centauri 2 (talk • contribs)
Out of Date
I agree! I made some little improvement. Albert00 , 04/2009
- It's indeed rather obvious, but the sentence added practically no information, so I think it should be removed anyway. --Roentgenium111 (talk) 20:38, 1 October 2010 (UTC)
I'm dubious about Due to differential heating, a tidally locked planet would experience fierce winds blowing continually towards the night side with permanent torrential rain at the point directly opposite the local star, the solar pole. It isn't clearly sourced by the ref given  and it doesn't fit with Joshi et al, where winds at 500 m vary from small up to ~15 m/s. I doubt that counts as life-threateningly fierce William M. Connolley (talk) 11:48, 3 October 2010 (UTC)
And I'm not clear how you can have winds continuously blowing in only one direction... forever? Surely at some point there would be an equilibration achieved. Or does the wind only blow like that at ground and sea level, with upper atmosphere currents carrying the air back? —Preceding unsigned comment added by 220.127.116.11 (talk) 06:39, 11 March 2011 (UTC)
In agreement with the previous posters, these two statements appear highly implausible and require either further clarification or removal. At the moment it appears to be a personal conjecture presented as fact with no supporting evidence. I have marked both statements as "citation needed". — Preceding unsigned comment added by 18.104.22.168 (talk) 09:37, 10 September 2012 (UTC)
Reference 16 "The end of the world' has already begun, UW scientists say'. Press release. Retrieved 2007-06-05." is broken —Preceding unsigned comment added by 22.214.171.124 (talk) 04:18, 2 March 2011 (UTC)
Megascale engineering to force faster rotation?
A bit of a far-out-there idea that I couldn't find any info about is the notion that an advanced civilization might try to give a tidally locked world a faster rotation, thereby undoing the locking, likely settling into a stable resonance, if possible. I imagine this could be achieved with a few non-contradictory methods in conjunction:
The first would be an extensive system of many thousands of tethers, like space elevators, but at an angle, attached to an array of solar sails, constantly tugging away at one of the sides of the planet to try to get it spinning faster (or at all in relation to its star). The combined force would have to be substantially larger than the tidal force that created the lock in the first place. If and when such rotation started, the anchor points could gradually be shifted. Once rotation sped up enough, the anchors could then be a mobile system on rails moving at a tiny but increasing rate (initially fractions of a millimeter per one of our days?) The continuous pull might bulge the crust and create artificial mountain ranges and hence a tidal effect partially or completely undoing the pull, so it would require considerable maintenance to lower or level the crust on the regions with the anchors.
Which leads to another approach, which is the creation of artificial mountain ranges on the opposite side of the planet, perhaps with the same mass removed from the anchor areas, thereby using tidal forces instead of just fighting them. As rotation increased, the mass would have to be continuously relocated, eventually becoming a mobile system like the anchor points on rails.
And the third approach I've thought of is that by shading half of the illuminated side of the planet, and reflecting light onto half of the dark side, the planet itself could be made an asymmetric, weak solar sail. A variation of this might be the use of focused light from a giant mirror or even a massive laser (like proposed beam-powered propulsion for starship propulsion), and this last option might be the only viable way to continue acceleration once rotation started with the above methods became too fast for anchor and mass relocation.
I'm guessing the timescale for all of this, if possible, would be on the order of millions, if not tens of millions of years. Solar sails or solar powered lasers and microwave emitters would have to be used as non-renewable propulsion forces (like ion engines) would quickly be exhausted over such massive timescales. It might be like asking an ant to tow a supertanker, but with enough time and continuous force, I imagine it could be done, and with the star providing a habitable zone lasting trillions of years, a worthwhile investment. Some might argue in favor of geoengineering/terraforming methods such as shading the light side and illuminating the dark, thereby expanding the habitable region, but these could be done in conjunction with the above: the same solar sails used to pull the tethers could be angled to illuminate the dark side (or at least half of it).
So, have I completely underestimated the viability of such an endeavor, or could a project like this possibly be done within the known laws of physics? (No Scrith or Tachyons here!) Has there ever been a proposal to alter rotation of such worlds, either in science fiction or as actual proposals? —Preceding unsigned comment added by 126.96.36.199 (talk) 07:51, 11 March 2011 (UTC)
- There doesn't appear to be any reason it couldn't work, except one: why would a society capable of it bother? It's far easier & more economical (in Δv terms, if no other) to simply build new structures from readily accessible materials. If they're going to attach solar sails, chances are, it's because they want the planet as part of a ringworld... TREKphiler any time you're ready, Uhura 09:52, 11 March 2011 (UTC)
- Glad that you think it's possible. The above was premised on the notion that an advanced civilization would consider planets as valuable and not just a feedstock for the creation of some sort of Dyson Sphere or a variant, though an actual ringworld violates the laws of physics. Despite what I wrote, I personally believe that intelligent life would come in the form of AI with nanotechnology taken to its theoretical potential and that planets would only be temporarily used by them until the matter composing the world had been consumed in the construction of the sphere, most likely a matrioshka brain, working on the premise that AI would want the most computing power physics and available resources allow. Under such a scenario, bothering to make the planet rotate in relation to its star would be a waste, like rearranging the deck chairs on the Titanic.
- But what's more, I'm not so sure that such AI & nanotech life would be limited to the narrow habitability ring (which, I admit, reminds me of a planet spanning version of Chile!) in the first place. Matrioshka brains' inner layer of "computronium" could be nearly as hot as the star it surrounds, while another example of super-high temperature computation comes from the later stages of Tipler's Omega Point formation. Tipler's wackiness aside, he believed AI life could exist and thrive beyond solid, liquid, gas, and plasma forms, even somehow transitioning to an elementary particle soup, and utilizing the Higgs field for computation. Both scenarios make the hot side of a tidally locked planet seem downright frigid in comparison. So maybe AI/nanotech life would have little need for temperatures we consider comfortable, and be it hot, cold, or just right would cover the entire surface of a tidally locked planet with computers idealized for that region's temperature. Boring to look at, but the real civilization would be virtual.
- So that leaves only a few scenarios in which a planet with a clement environment not limited to a thin ring would be ideal. One is the possibility that I'm wrong and advanced life would still be organic and would want and need planet-wide habitability, and the other is that the advanced civilization would want to make the planet more habitable for others, like a big zoo or nature preserve (a variation of the zoo hypothesis?), maybe a place to transplant life from other worlds. (though a fatal flaw with this could be the possibility of a stable resonance other than 1:1 not "taking" and an inevitable "relocking" after some millions of years. Continuous intervention to maintain rotation would periodically disrupt and maybe not be worth it like a single, permanent effort.) Taking all that time and effort to spin up the planet might strike some as a waste of resources, but with an eternity of space, and a continuous, couple trillion year supply of solar power, why not do it? Dedicating the resources to something like interstellar travel would be pointless as colonization of all nearby systems and beyond would have long ago been achieved, most likely with von Neumann probes. The Egyptians built the pyramids, and similarly an advanced civilization may have nothing better to do. —Preceding unsigned comment added by 188.8.131.52 (talk) 07:11, 14 March 2011 (UTC)
I don't see a reason for brown dwarfs to be mentioned in the second paragraph of this article. I propose that it should be removed. — Preceding unsigned comment added by 184.108.40.206 (talk) 23:35, 23 March 2012 (UTC)
Right - I think the article would benefit from some examples - haven't some planets been found around red dwarfs already? Improving sourcing (obvious). More to come later. Cas Liber (talk · contribs) 00:09, 21 July 2013 (UTC)
- NB: A bit hard to work on prose extensively until the article is more fully sourced. Occasionally this yields surprises as one has to change hte content to reflect updates in sourcing....Cas Liber (talk · contribs) 00:15, 21 July 2013 (UTC)
"The point directly opposite the local star"
This formulation is ambiguous since it could mean either the point where the star appears at the zenith (also known as the subsolar point) as well as the point 180 degrees away, i.e. the midpoint of the night side. From the context (heavy rain due to strong upward convection), probably the former is meant, i.e. the subsolar point. Th clear this ambiguity I have rephrased that sentence.--SiriusB (talk) 17:02, 17 November 2013 (UTC)