Want to read Slashdot from your mobile device? Point it at m.slashdot.org and keep reading!


Forgot your password?
Space Science

Tidal Heating Shrinks Goldilocks Zone Around Red Dwarfs 70

scibri writes "An overlooked factor could shrink the habitable zone for planets around M-class dwarf stars by as much as 50%. For these smaller, cooler stars, the habitable zone was thought to extend to relatively close orbits. But as you get closer to a star, the tidal force it exerts on a planet increases. Since planets do not have perfectly circular orbits, tidal forces cause the planet to flex and unflex each time it moves closer to or further from its star; kneading its interior to produce massive quantities of frictional heat — enough to scour the planet of any liquid water. Because M-class dwarf stars are the most numerous in the galaxy, and close-in planets are easier to spot than more distant ones, such stars have been a major target for planet hunters seeking Earth-like worlds. But now it seems we may have been looking in the wrong place for Earth's twin."
This discussion has been archived. No new comments can be posted.

Tidal Heating Shrinks Goldilocks Zone Around Red Dwarfs

Comments Filter:
  • by Anonymous Coward

    Earths twin would be a planet of the same size, orbiting a star of the same size and characteristics, in the same way.

    I think you mean "planets that may have water".

  • Friction is hell (Score:4, Insightful)

    by smittyoneeach ( 243267 ) * on Tuesday May 08, 2012 @02:48PM (#39931641) Homepage Journal
    Friction is hell
    In space or on face
    Sudsy blade orbits
    Don't leave a trace
    Burma Shave
  • by Anonymous Coward

    What about moons around large planets? Similar, no?

  • by Jeng ( 926980 ) on Tuesday May 08, 2012 @02:54PM (#39931763)

    Funny, I don't remember that one.

  • by dkleinsc ( 563838 ) on Tuesday May 08, 2012 @02:55PM (#39931771) Homepage

    That smeghead makes everything around Red Dwarf uninhabitable.

  • Goldilocks didn't have any dwarfs! Geez...
    • by Jeng ( 926980 )

      It is never explicitly stated that Goldilocks did not associate with Dwarfs.

      Teach the Controversy!

  • by anwyn ( 266338 ) on Tuesday May 08, 2012 @03:03PM (#39931907)
    Why does this arguement not show that there are places that should be to cold, but are not because of tidal heating?

    Could someone please explain this to me?

    • by bored_engineer ( 951004 ) on Tuesday May 08, 2012 @03:10PM (#39932033)
      In the context of red dwarfs, it's about distance. Gravity falls off with the square of the distance from the source. So, as the distance increases, the influence of the primary would fall off, thereby reducing the tidal heating. I suppose that it could heat a planet orbiting a brown dwarf, but a brown dwarf would have no (or little) emissions in the visible spectrum. Perhaps something besides terrestrial life could find it habitable, but I don't think we would be able to live there.
      • What about other small, bright, and dense objects?

        A white dwarf, for instance?

        You also discount the potential for exotic photosynthetic life around the brown dwarves. For instance, here on earth normal green photosynthetic plants can absorb multiple photons of red freq light and combine the energy from them with some clever quantum mechanics to have enough energy to push a high energy electron into a chemical bond site.

        It doesn't seem inconcievable that there could be very slow respiration organisms that h

        • A white dwarf, for instance?

          A white dwarf doesn't last for long and is a relic of a previous red giant that has been thoroughly baking your planet for quite some time. If you look upon the sky and see a white dwarf as your sun, check your pulse, since you're most likely a ghost.

          • by Anonymous Coward

            Actually, a white dwarf lasts forever (i.e. significantly longer than the age of the universe), unless it's unlucky enough to have a companion dumping mass on it to exceed the Chandrasekhar limit. Of course, the preceding giant phase is problematic, but it does make for nice, sterile systems for an expansionist civilization -- might be the place to look for advanced ETI?

        • . . .but a brown dwarf would have no (or little) emissions in the visible spectrum. Perhaps something besides terrestrial life could find it habitable, but I don't think we would be able to live there.

          You also discount the potential for exotic photosynthetic life around the brown dwarves.

          I only discount the possibility that such a planet would be sufficiently earth-like to be habitable to you and me, or even to the spruce trees outside my window. I chose to limit my comment because the topic of both the summary and the article is earth-like worlds. As you did, I can visualize some sort of life there, I just can't see ours living there.

          I'm not an astrophysicists, but wouldn't the spectral emissions of a white dwarf be a little rough on terrestrial-like life? Again, I think that it would b

          • The world would be "dark", or a deep wine red colored in terms of "daylight", but with oxygen producing photosynthesis, and tectonic warming, the planet would have a "habitable" biosphere, you would just need a flashlight everywhere you go.

            Any animal forms would be either blind, or have very large, flat eyes, or just eye spots. (Red light is low energy, and is scattered easily. IR and nIR are absorbed by water, so the vitreous humors in these hypothetical creature's eyes would pose a hidrance to photon con

            • I'll defer, as you've clearly given it more thought than I'm willing to do. I did enjoy reading the setting that you've proposed, and you'll have to let me read your story, should you write it.
      • by Anonymous Coward

        Tidal effects fall off with the cube of the distance, not square. Radiant energy from the star fall off with the square. Since tidal effects fall off much faster, the inner boundary of the Goldilocks zone is pushed back farther than the outer edge would be.

    • In TFA they say that people looking for Exo-planets are looking for ones with close orbits. They believe now that because of tidal forces those planets would have hotter temps and not be candidates for a Earth-like planet.

      Looking for close orbit planets is a fine way to find exoplanets.

      What they should say is that looking for close orbit planets is not a good way to find earthlike planets with liquid water.

      Now take in your head the originally believed habitable zone, you are going to have to shorten that on

    • by Lithdren ( 605362 ) on Tuesday May 08, 2012 @03:15PM (#39932095)
      I dont see anything that claims thats not possible, so I dont quite get where you get this from. It would be a strange place indeed, a planet warmed by tidal friction from within would have a very different biology of life. I'd imagine most life would be deep underwater near rifts in the oceans floor, there'd be no point in forming near the surface, depending on what caused the tidal forces.

      Would make for an interesting long-term strategy for an advanced race to survive past the life of stars, if you can heat from within via tidal forces around say, a super massive black hole. Just dont be the jerk to mess that one up.

      "Sir! We forgot to exchange values between Metric and Imperial, the entire planet is about to get sucked into a black hole!"
      "Well...alteast we dont need to worry about budget cuts next year."
    • I was thinking that. Surely for smaller stars, there's still a "Goldilocks zone" where stellar input + tidal heating = just the right amount of heat. It may be considerably narrower than the Sun's, but there are so many more red dwarfs than there are Sun-like stars that I'd expect the numbers to even out. Add in the extremely long lifetimes of smaller stars, and it seems like red dwarfs are still good candidates for extra-Solar-System life.

      • Once the tidal heating contribution to the total thermal budget is significant, you can be sure it won't last for long. It wouldn't last the 4,300 My that are the age of Earth, and the 10 Gy that are the lifetime of our Sun. The even longer lifespan of a dimmer star hardly compensates for it. Life needs time to emerge and to evolve, and rather stable conditions as well. We on Earth happen to be fortunate, the hypothetical Reddwarfeans wouldn't be.
      • Smaller stars (like Sol) generally output much more heat, so the habitable zone due is much farther away from the edge of the start than for a larger, cooler star (from TFA).
        As such, once you get out to the right distance (for Sol, it's between the outside of Venus' orbit to the inside of Mars' orbit, right about where we are), tidal forces from the primary no longer have the same warming effect that could boil away the oceans.
        Remember, our tides come from our satellite (luna), and it doesn't exert enough
        • by G00F ( 241765 )
          <quote>Remember, our tides come from our satellite (luna), and it doesn't exert enough force on us to mess up the Earth's core (just move our oceans around a bit)</quote>

          Actually I believe our moon is highly responsible for earth still having a molten core, and a good strong protective magnetic field with it.
    • It probably does, but the effect would be minimal since at the outer edge of the Goldilocks zone the gravity gradient is going to be very small.

    • It does work both ways, where did you get the idea it doesn't? The fact that planets closer to their star may be warmer then expected is more relevant though, since that's where astronomers tend to look for planets.

    • by Hentes ( 2461350 )

      As tidal forces depend on gravity, they push the inner boundary of the zone much further away than they push the outer one, thus the zone itself shrinks.

    • by Surt ( 22457 )

      If your planet is too cold, it is because it is too far from the star. If it is too far from the star, it isn't getting tidal heating either. This legitimately puts a cap only on one end of the range.

    • Io and Callisto are the same distance from the Sun, but Io is a _lot_ hotter. If you get far enough from a red dwarf sun to be too cold, the tides are a lot weaker.
    • This makes me think that most of these planets are tidally locked to their parent star. They are very hot on the side facing the star and cold on the other side.

      If you put tidal heating on the formula, maybe those freezing dark sides are not so freezing after all.

      • If they are tidally locked, there won't be any tidal heating.

        Life like we need a planet at the habitable zone, with tick athmosphere (to hold water), and not tidally locked into its star.

  • I would have assumed that tidal locking would eventually cause more trouble for life than tidal heating does good.
    • by Jeng ( 926980 )

      Yes, but depending on atmosphere a tidally locked object will have 2 habitable zones, well I guess really one ring-like habitable zone.

      • The thing is that if the planet is made habitable and fit for life to spring into existence on it to a significant degree due to tidal heating, once the tidal heating stops due to tidal locking, the conditions on the planet will have been drastically altered by this (day length, averages of temperatures in various points on the surface, eccentricity and semi-major axis, year length...). The question is whether any higher life forms could adapt to such a change. This could really lead to extreme changes, and
        • --The question is whether any higher life forms could adapt to such a change--

          That is THE big question and you sure know how to ask it.

        • Even if the environmental changes from tidal locking wiped out most advanced lifeforms plenty of microbes and extremophiles would almost certainly survive. Since dwarf stars have a MUCH longer lifespan than larger stars there would be likely be plenty of time for more advanced life to evolve multiple times over.

          As for winds and weather, I imagine they would actually be (relatively) mild near the day/night poles, but strong and steady near the twilight ring, with cold,dry air flowing dayward at the surface

      • I didn't think in general a tidally locked planet was habitable, in a tidally locked planet the dark side becomes a cold trap, freezing out the atmosphere - unless you get massive recirculation of heat due to oceans, even if you did have a favorable configuration of the contents plate techtonics would likely eventually push you into an unfavorable configuration, causing the atmosphere to freeze out, once that happens, its over.
  • "But now it seems we may have been looking in the wrong place for Earth's twin."

    Why do people feel compelled to say things like this? There are multiple reasons why we will continue to be motivated to identify planets orbiting M-class stars. The most compelling is perhaps that we simply don't yet know the full range of potential planetary scenarios, both the types of orbits they might adopt and the material nature of the planets themselves. We can't yet even anticipate the full range of unique conditions that might make a planet habitable (for humans much less otherwise). The more

  • Researcher was probably reading Neutron Star and went 'Oh, Crap!'

  • by Anonymous Coward

    The article fails to mention that although the habitable zone would shrink closer to the sun, it would expand further from the sun. Tidal forces obey a power law, so this expansion on the far side would not be as great as the area lost on the near side, but it does open up some interesting possibilities, such as having a dark, warm planet.

    • by JTsyo ( 1338447 )
      That would only work on a really weak star. If you're far enough from the star that you aren't receiving enough solar energy, then you're too far for tidal effects.
  • Worst Disney Mashup ever.
  • by Immerman ( 2627577 ) on Tuesday May 08, 2012 @09:00PM (#39936611)

    They compare to Jupiter's moon Io in the article, whose proximity causes tidal heating and makes it the most geologically active body in the solar system. However, all the energy that goes in to tidal heating is drawn from its orbital energy and would normally cause the orbit to circularize (tidal dissipation), thus eliminating the heating - the only reason that doesn't happen with Io is because it's locked in a 1:2:4 orbital resonance with Europa and Ganymede, both of which have much greater orbital energies.

    Now I imagine this would take longer with a planetary-sized orbit than with a moon-sized orbit, but unless the planet migrated inwards considerably I would expect that it would have largely occurred while the proto-planetary cloud was still coalescing. It might contribute to a longer cooling period, but I don't see how that's really a problem, it's not like a lot of these dwarf stars aren't considerably older than Sol, even a few billion extra years years of cooling would still give life there a head start on us. In fact, considering that Earths volcanic phase is when life here got it's start, a mechanism that might have extended that period seems like it could make life even more likely.

    • Also worth pointing out that even if a red dwarf planet's orbit were perturbed by other worlds, as is the case with Io, you won't get strong heating. The distances between a red dwarf's planets will be far larger than the distance between Jupiter's moons, so the orbital perturbations will be much *much* weaker.

"If it's not loud, it doesn't work!" -- Blank Reg, from "Max Headroom"