Talk:Habitability of red dwarf systems

Comments

Is it possible for organisms around red dwarf to use thermosynthesis instead of photosynthesis? And can't the photosynthesis be done using infra-red radiation? Grzes (talk) 14:53, 9 May 2008 (UTC)

If we ever find extra terrestrial life it will probably be totally different from what anyone expected. Proxima Centauri 2 (talk) 09:15, 22 May 2008 (UTC)

Comments

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)

Well, the planet's temperature wouldn't be ~3000K (the backbody temperature of incoming light), so no problem there.

flare stars

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

This article is woefully incomplete and out of date. I hope to find time to add stuff. Vegasprof (talk) 02:06, 7 January 2009 (UTC)

I agree! I made some little improvement. Albert00 , 04/2009

Concerning references, Scientific content has been small and biased for about 50 years, largely ruling out red dwarf systems from Habitability, with little justification and few exceptions. The article is weak because it draws from a weak history of references. Botany science shows that most plants use the red light of the spectrum and largely ignore other colors. So from that perspective red dwarf habitats would be preferred, if a few other requirements are met, like liquid water and non toxic atmosphere. Red dwarfs cover a large range of sizes and masses, giving the larger red dwarfs a reasonable chance to support a habitable zone. Planetary science has found a large number of super earth sized planets, many of them in red dwarf systems. In such strong gravity aquatic life would have an advantage, although terrestrial life is not ruled out.

Habitability has different meanings to different writers, concerning whether or not life arises by natural processes and survives a variety of climates and epochs, or is transplanted from some other place to a suitable microclimate. As far as earth science can determine, life began once and only once on earth, now greatly diversified by genetic modifications, but all still using the same original genetic language, the same highly specific small group of fundamental building blocks, and the same genetic code. Science doesn't find a variety of genetic codes and languages with alternative building blocks in various stages of development. Thus the chance of life occurring naturally anywhere is fairly small, but the chance of transplanted life surviving and adapting is fairly large.

Life time of red dwarfs is very long on the main sequence of stars, such that they have much longer time periods available for developing habitable conditions than more massive stars.

Flare stars among red dwarfs would prevent much of terrestrial surface life, but not sub surface and aquatic life. Tidal locking seems likely from solar system examples, but can also be an advantage of moving the habitable zone farther from the star, making a variety of climates from tropical to arctic, alternating perpetual sun light and rain clouds moderated by cold winds from the dark side. In 60 billion red dwarfs, the chances seem rather good for habitability, but the science is weak and the references are unsound. So I refrain from rewriting the article, although it is needed. Astrojed (talk) 00:40, 23 April 2016 (UTC)

GHE

I'm not sure about this [1]. It is, in essence, simply obvious and barely needs citnig. But Joshi et al. would do as a cite if one is needed William M. Connolley (talk) 20:00, 1 October 2010 (UTC)

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)

Fierce winds

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 [2] 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 4.254.82.252 (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 86.29.123.227 (talk) 09:37, 10 September 2012 (UTC)

Using Earth and Venus examples low surface pressure occurs in warm regions and high surface pressure is typical of cold regions. In tidal locking the "fierce winds" would be from the dark side to the light side in low altitudes, with reverse flow in upper atmosphere. Astrojed (talk) 23:58, 22 April 2016 (UTC)

References

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 187.104.234.227 (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 4.254.82.252 (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 4.254.81.251 (talk) 07:11, 14 March 2011 (UTC)

Brown Dwarfs

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 216.246.130.20 (talk) 23:35, 23 March 2012 (UTC)

Pre-GA feedback

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)

Abundance and size of planets in the habitable zone

Hi. Very interesting article here. I have a fundamental issue though, that I would like to adress.

Almost all of the article is devoted to discussing eventual habitability of a given planet in the habitable zone of red dwarf stars. But from the current disk models of general stellar formation, red dwarfs will not contain very much material within the central one AU or so. This means that Earth-sized planets (or larger) cannot form in the central parts and the habitable zone of red dwarfs are exactly confined to these central regions. Alas, red dwarfs are unlikely to have any Earth-sized (or larger) planets in their habitable zones. This conclusion has important consequences for the habitability of planets originally formed in the habitable zone, because smaller planets cannot retain any significant amount of volatiles due to their smaller gravity.

There could be super-Earth planets in the habitable zones though, in some rare cases. If they migrated there from further out for some reason or if the red dwarf captures lonely vagabond planets or planets from other star systems for some odd reason. But these would be uncommon events. And it would indeed complicate the determination of habitability of these planets.

The overall problem is discussed in relation to Proxima Centauri b here: Anglada-Escudé, G.; Amado, P. J.; Barnes, J.; Berdiñas, Z. M.; Butler, R. P.; Coleman, G. A. L.; de la Cueva, I.; Dreizler, S.; Endl, M.; Giesers, B.; Jeffers, S. V.; Jenkins, J. S.; Jones, H. R. A.; Kiraga, M.; Kürster, M.; López-González, M. J.; Marvin, C. J.; Morales, N.; Morin, J.; Nelson, R. P.; Ortiz, J. L.; Ofir, A.; Paardekooper, S.-J.; Reiners, A.; Rodríguez, E.; Rodrίguez-López, C.; Sarmiento, L. F.; Strachan, J. P.; Tsapras, Y.; Tuomi, M.; Zechmeister, M. (25 August 2016). "A terrestrial planet candidate in a temperate orbit around Proxima Centauri" (PDF). Nature. 536 (7617): 437–440. doi:10.1038/nature19106. ISSN 0028-0836.

Does anybody know of sources discussing this crucial issue in more detail for red dwarf stars in general? That would be a great contribution to this page if we could present a ref pointing to such a general discussion. RhinoMind (talk) 23:58, 6 September 2016 (UTC)

I've also been wondering about this question since reading about Proxima Centauri b's formation history. But note that the paper you cite talks about "small stars", not red dwarfs specifically. Maybe red dwarfs that are larger than Proxima have more available material? After all, we also have the HARPS result to which the last sentence of the article's lede refers: "About 40% of all red dwarf stars have a super-Earth orbiting in the habitable zone".[3] --Roentgenium111 (talk) 16:25, 8 September 2016 (UTC)

Hi and thanks for the ref in particular. Whatever the general truth might be (or the current understanding), it is of fundamental importance to what this article is about. And therefore we need to adress it somehow in the article. I was also led to the issue by PCb's formation history and what was said about stellar models and it would be great if we could track down some of the papers on disk models for small stars (or red dwarfs in general) to include here. Perhaps there is some clues in the paper I mentioned above. And for the ref you mention it would also be great to track down the peer reviewed ESO papers that talks about this. A press release is a bit superficial, but at least it gives us a good hint that there is some science behind it, when it is announced by ESO themselves. Thanks for engaging in this, it is an important issue for this article. RhinoMind (talk) 16:45, 8 September 2016 (UTC)

Hi, the ESO paper is here: Abstract, full paper. It states that the probability of 41%(+54%/-13%) was calculated from just two HZ planets detected, explaining the large error bars.

Edit: About 90% of the 102 red dwarf stars in the study's sample are larger than Proxima (Fig. 1). The two stars with habitable-zone planets found (Gliese 581 d, Gliese 667 Cc) both have about 0.3 solar masses, so they're both more than twice as massive as Proxima. --Roentgenium111 (talk) 17:26, 8 September 2016 (UTC)

Great stuff there, especially the uncertainties you dragged out. Still we also need some more detailed info about these "disk models for smaller stars" that were mentioned. This is also crucial info. Even though we might find super-Earths around red dwarf stars (or "smaller stars" whatever that means), we can not tell (at the moment) if they were created there in the first place. Just stating. RhinoMind (talk) 18:24, 8 September 2016 (UTC)

Just wanted to note that I haven't forgot about this issue and I will try to implement the information you provided when I find the time. I encourage anyone reading this to go ahead too. RhinoMind (talk) 14:53, 17 September 2016 (UTC)

Hot wind

". . . it was argued, a tidally locked planet would experience fierce winds blowing continually towards the night side . . ." For this alleged hot wind we have failed to find a citation, and my argument is for the opposite direction. Hot air rises, which means air cooled on the night side would descend and move along the surface as a cold wind towards the day side where it would rise and return at high altitude. Perhaps also a Coriolis Effect would turn this motion to make it stronger along the terminator than across it, just as winds on Earth are more along latitude lines than across them, though I feel less sure about this part. Anyway, lacking citation, we should not use my argument but merely get rid of the proposed wind direction. Jim.henderson (talk) 13:01, 16 September 2016 (UTC)

Hi. Glad you point to the missing ref on this issue and document it here. That will improve the chance that a proper ref will be provided. And if not, the OR info will be removed.

About your "windy thoughts": A strong prevailing wind would have to be circular by basic physics (and logics). In an isolated system - such as a round planet -, no wind could go in any direction without being replenished by an opposing wind. From that alone, highlighting a specific direction makes no sense. An issue you also touches in your comment. RhinoMind (talk) 15:04, 17 September 2016 (UTC)

Well, it can loop vertically. The counterflow of surface wind can be at high altitude, leaving at least a few places on the surface with mostly just updraft and downdraft, bereft of a dominant surface wind direction. This is roughly how the atmosphere of Mars does it, or part of how polar cells act on Earth. Except, in both cases, the surface wind is somewhat circular due to Coriolis, though the pattern is not displayed as neatly as in the atmosphere of Jupiter. I would expect some sort of surface circularity to develop on our hypothetical world, but my mind boggles at trying to imagine the details. Perhaps someone has actually studied and published, somewhere. Jim.henderson (talk) 13:49, 21 September 2016 (UTC)

Orbital Eccentricity?

If a tidelocked planet had even the tiniest bit of orbital eccentricity and axial tilt, it'd have a day/night cycle on parts of it. We see 60% of the Moon's surface, and it has no air for atmospheric lensing and not much orbital eccentricity or axial tilt. So it...wouldn't actually have a stationary terminator line. The Moon doesn't have a line where the Earth is permanently on the horizon so why would a tidelocked planet? 118.92.181.27 (talk) 01:44, 3 July 2017 (UTC)

I guess you are talking about the first paragraph in the "Tidal effects" section? I have inserted an explain-tag now. Hopefully some skillfull editors could elaborate more on that section. And hopefully they will insert in-line refs as well?

I have to say though, that the terminator is described as a zone and in that respect includes the small variability that you are discussing. I also have to say that I don't think the eccentricity could be very pronounced for tidally locked planets in close orbits. But I am just expressing my gut feeling about this. It would have to be reffed and explained further in the article. RhinoMind (talk) 20:34, 3 July 2017 (UTC)

I mean...even if it had the exact same amount of orbital eccentricity and axial tilt as our moon does, 20% of it would still have day/night cycles. And looking at an orbital eccentricity table, the eccentricities of gravitationally locked objects range from 0.00002 (Triton, orbits retrograde for some reason) to 0.2056 (Mercury, locked in a 3:2 resonance, has the greatest eccentricity of all the planets).

Also, there was mention of tidal heating potentially warming the planets up too much-doesn't that mean that those planets aren't actually in the habitable zone and it's really somewhat farther out? 118.92.179.16 (talk) 01:33, 4 July 2017 (UTC)

1. Detectable planets would have to be much larger than the Moon. I mean MUCH larger. This will decrease the area-percentage of the terminator-zone considerably. However, no-where in the text is it postulated that the terminator would be insignificant in size. So nothing is wrong, it just might need some further explanation. All tidally locked bodies close to a hot star will have a blazing hot side/area and a freezingly cold side/area. No terminator zone could change that. A broad terminator might just diminish the extreme hot and cold areas somewhat. It is a solely geometrical issue.
2. tidal heating. Might reply more elaborately later. But... as I understand it the habitable zone is only based on the stars radiation. All other effects are "extra" and might increase or decrease the habitability of a given planet in a given system. However, mass and raditaion are linked so that massive stars have intense and hard radiation pushing the habitable zone far away from the star, and light-weight stars (such as red dwarf stars) shine with low intensity and less energetic radition, drawing the habitable zone closer. This will in itself prevent the situation you mention in any habitable zone. Admitted, I am not an expert of the details of habitable zones, so I am just airing my general understanding.

RhinoMind (talk) 22:19, 4 July 2017 (UTC)

Ad.2 This article might be of interest: Circumstellar habitable zone RhinoMind (talk) 01:03, 8 July 2017 (UTC)

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Years

Potentially habitable planets in red dwarf systems have shorter years that Earth's year. — Preceding unsigned comment added by 46.10.141.174 (talk) 20:01, 11 April 2018 (UTC)