Update on Gliese 581d’s Habitability


When last we checked in on Gliese 581d, a team from the University of Paris had suggested that the popular exoplanet, Gliese 581d may be habitable. This super-Earth found itself just on the edge of the Goldilocks zone which could make liquid water present on the surface under the right atmospheric conditions. However, the team’s work was based on one dimensional simulations of a column of hypothetical atmospheres on the day side of the planet. To have a better understanding of what Gliese 581d might be like, a three dimensional simulation was in order. Fortunately, a new study from the same team has investigated the possibility with just such an investigation.

The new investigation was called for because Gliese 581d is suspected to be tidally locked, much like Mercury is in our own solar system. If so, this would create a permanent night side on the planet. On this side, the temperatures would be significantly lower and gasses such as CO2 and H2O may find themselves in a region where they could no longer remain gaseous, freezing into ice crystals on the surface. Since that surface would never see the light of day, they could not be heated and released back into the atmosphere, thereby depleting the planet of greenhouse gasses necessary to warm the planet, causing what astronomers call an “atmospheric collapse.”

To conduct their simulation the team assumed that the climate was dominated by the greenhouse effects of CO2 and H2O since this is true for all rocky planets with significant atmospheres in our solar system. As with their previous study, they performed several iterations, each with varying atmospheric pressures and compositions. For atmospheres less than 10 bars, the simulations suggested that the atmosphere would collapse, either on the dark side of the planet, or near the poles. Past this, the effects of greenhouse gasses prevented the freezing of the atmosphere and it became stable. Some ice formation still occurred in the stable models where some of the CO2 would freeze in the upper atmosphere, forming clouds in much the same way it does on Mars. However, this had a net warming effect of ~12°C.

In other simulations, the team added in oceans of liquid water which would help to moderate the climate. Another effect of this was that the vaporization of water from these oceans also produced warming as it can serve as a greenhouse gas, but the formation of clouds could decrease the global temperature since water clouds increase the albedo of the planet, especially in the red region of the spectra which is the most prevalent form of light from the parent star, a red dwarf. However, as with models without oceans, the tipping point for stable atmospheres tended to be around 10 bars of pressure. Under that, “cooling effects dominated and runaway glaciation occurred, followed by atmospheric collapse.” Above 20 bars, the additional trapping of heat from the water vapor significantly increased temperatures compared to an entirely rocky planet.

The conclusion is that Gliese 581d is potentially habitable. The potential for surface water exists for a “wide range of plausible cases”. Ultimately, they all depend on the precise thickness and composition of any atmosphere. Since the planet does not transit the star, spectral analysis through transmission of starlight through the atmosphere will not be possible. Yet the team suggests that, since the Gliese 581 system is relatively close to Earth (only 20 lightyears), it may be possible to observe the spectra directly in the infrared portion of the spectra using future generations of instruments. Should the observations match the synthetic spectra predicted for the various habitable planets, this would be taken as strong evidence for the habitability of the planet.

47 Replies to “Update on Gliese 581d’s Habitability”

  1. The new investigation was called for because Gliese 581d is suspected to be tidally locked, much like Mercury is in our own solar system.

    What?! Actually, although it was once thought that the planet Mercury’s rotation was tidally locked with the Sun, radar observations in 1965 proved that Mercury has a 3:2 spin–orbit resonance with the Sun, rotating three times for every two orbits.

    1. “This is thought to explain Mercury’s 3:2 spin-orbit resonance (rather than the more usual 1:1), since this state is more likely to arise during a period of high eccentricity.”

      So that is another possibility then. Planets like Gliese 581 d is nominally 0 eccentricity at this time, as Mercury, but that could be happenstance, as Mercury. (But there is no Jupiter in the Gliese system specifically.)

  2. I’m not sure we can arrive at any definitive conclusions as to whether Gliese 581d is tidally locked. If it’s determined that this exoplanet is tidally locked, the chance that the planet harbors life is very slim.

  3. No mention of atmospheric circulation patterns? I remember the discussion on this planet and it seemed likely that such huge variations in surface temperature would generate perpetual hurricane force winds (depending on atmospheric density).

    Also, there is the matter of Gliese’s parent star. Those red dwarf stars are more variable and often belch a lot of radiation.

  4. A spin-orbit resonance other than 1:1 occurs if there is some asymmetry in the matter distribution of the spinning planet. Mercury is in some such configuration as I remember.

    If this planet Gliese 581d is habitable it could mean that the majority of biologically active planets in the universe are those around red dwarf M class stars.


    1. This is a good point if the inward migration model proves to be the dominant model for planetary systems. The jury is still out though on just how often this occurs. These are exciting times in this area of science.

    2. Perhaps; but as IAL link describes it, it is the presence of a large Jupiter that does it. Not as common a planet as superEarth massed ones, according to Kepler.

    3. need to get back to my numerical model of the Gliese 581 system. My work on the conformal completion of AdS as equivalent to n-partite quantum entanglements proves to be a many-multi-year deep program. As a result I have not returned to these simulations I started last October.

      One thing which has me concerned is the long term stability of such a stellar system of planets. The planets are fairly massive and they all orbit within less than 2AU of the parent star. Their mutual gravitational perturbation would likely perturb them quite heavily. These orbits might then chaotically adjust with time. As a result a planet in the so called Goldilocks zone may not stay there for terribly long. This happens with our solar system to some extent, but I computed the outward drift of the Earth orbit due to Jupiter’s influence to sufficiently compensate for the increased luminosity of the sun as it evolves. The close proximity of these planets in these mini-solar systems means their mutual gravitation is considerable. They would then mean these orbit-orbit interactions will be strong.

      As for evidence of alien life, mentioned below, there is of course absolutely none. This does not mean it does not exist, or that astronomers hypothesize it does not exist. There is a lot of universe out there, and the chemistry leading to life is most likely not something utterly exceptional to Earth so as to be one cosmic fluke. So it probably is repeated with some average frequency amongst planet around other stars. It may even occur on Mars, though that is very close so as to be maybe not independent of Earth, and some of the Jovian-Saturnian moons are conjectured to maybe have life in subterranean oceans and the like. It is then entirely reasonable to think biology likely emerged from chemical or geochemical processes elsewhere on other planets. Yet, as yet we have no observational data to support this.


  5. why is universe today always on the negative side? talking about alien life, universe today says no evidence of alien life. talking about habitable planets, universe today says only earth is habitable. could you ever try not to be selfish? try to think of positively that we are not alone in the universe. try thinking that we have brothers and sisters out there.

    1. “universe today says no evidence of alien life.”
      That is not evidence, is is an actual truthful plain fact.
      Do, YOU, have any evidence of alien life that we don’t know about?

    2. Universe Today does not try to be either, but instead reports on the scientific evidence as it is released. We don’t refute or promote anything but what’s either currently accepted by researchers or, if a hypothesis under study, will be noted as such. While everyone has beliefs or hopes of something or other UT does try to remain impartial when reporting on things, although the trend will always be with science and away from pseudoscience.

    3. marlon, what good it would be to write an article about alien life somewhere around Gliese 581 and fool people when nobody has absolutely no clue? I surely hope someone will find the evidence in my lifetime, but until then there’s no point in publishing sci-fi stories on serious websites.

  6. Dude, I post from my BlackBerry almost exclusively and I you never see garble like that in my posts. You may have had something very insightful to add but I gave up mid point of the second sentence.

    1. I think this post is from somebody who is not an English speaker, and the reference to U Paris suggests they are French. If I wrote in French I am sure it would be rather garbled, and worse if I wrote po Russki.


      1. Wuz & teh are both common terms in as Torbjorn put it “LOLSpeak.” (Nice term btw gunna have to use one someday)

        If you hang around any underground message boards you’ll see used often. It started as a way of keeping sensitive posts & discussions from popping up in search engine results.

        I guess it could be worse he could have posted using ascii. Reading THAT is hard on the eyes!

      2. I spos so, the riter menshuned Paris, but the artacl discus teh results of U Paris grup. So my suposishun he was franch wus rong.


      3. he rewrote the first paragraph of the article using a “lolspeak” text generator. very lame.

  7. I have a few questions I’m sure a few ppl here can probably answer off the top of their heads.

    1. How fast is it possible to get a probe going using only available technology?

    2. How long would it take to get to this system? Including deceleration so we would get more than a passing look.

      1. You wouldn’t happen to have a link to this article on physorgs mirror wap site would you? I’m on my BlackBerry as usual. If it was on physorg the odds are almost 100% that I have already read it physorg’s pda site is the best thing on the internet IMHO. I read the “Space Exploration/Earth Sciences” and the “General Physics” categories almost every day.

        I can look it up when I get on my computer later.

      1. Jeez! I was interested in purchasing it until I saw the 95 dollar price tag. I like hardcovers as much as the next guy, but maybe consider a paperback next time. For 20 bucks I’d buy that – for 95 I never would.

  8. Hi, carbon copies;-)
    nuclear powered aircraft carriers and submarines can do without refueling for 20 years, so it should be possible to send a nuclear powered probe to check the situation though we have to be patient… very much so:-).
    But first we should check out our backyard. 1. robotic probes, which do a good job in paving the way for 2. human missions. Mars can be visited within the next 5-10 years to
    a) setting up a human presence and b) to prepare for possible Terra-forming. As the Space X CEO (a real visionary!) lined out they have a super heavy lifter withing 5 years to send all equipment and people there… I wonder when Bill Gates and consorts will open their purses to finance missions???
    As George Burns said: look to the future, because there you spend the rest of your life!
    Let’s go.
    The US has been to the moon a loooong time ago, why wait? Todays technology is, admittedly, somewhat better, right? HAHA

  9. I fully agree we should concentrate our efforts on this solar system unless we were to find an exoplanet nearby that had say an abundance of oxygen in its spectrum or something.

    Just figuring off the top of my head if this system is 20 light years away and I seem to recall that even .10 of light speed was currently unattainable, so assuming a maximum speed of .05 of LS. That would put travel time at 400 years, plus another 50ish for acceleration and deceleration. So by my very crude estimate we’d be looking at between 450 & 500 years of travel time.

    That is of course assuming that somehow the thing manages to avoid the purple star plasma, low rider, inverted liquid schwartz, high octane, electricity field that permeates the interstellar medium.

    1. IIRC anything much higher than 10% of the speed of light is impractical. At 0.1c a combination of a forward projected magnetic field and an extremely large, heavy physical shield could protect you from interstellar debris. At 0.3c an individual dust grain would do as much damage to your spacecraft as running into a small asteroid at lower speeds…and there is a lot more dust out there than asteroids;). Even 0.2c is still to fast for a ship to be able to survive contact with dust particles.

      That v^2 bit in the kinetic energy equation is a killer, literally. (And of course at higher speeds still relativistic effects start to play a more significant role, increasing the danger further.)

      1. The practical limit for propulsion systems is .1c. Fusion is the only plausible propulsion system now, and that is still a technical TBD. To get beyond .1c with a propulsion system on the craft will require some direct conversion of mass to energy. The obvious one is antimatter, but as yet we have no way of producing large amounts of antimatter. The understanding of quantum field theory as it connects to gravity, or quantum gravity, might give rise to physics which permits the violation of baryon numbers. If so then we might be able to convert matter into energy. However, that is what might be called exotic physics and technology. This would be a relativistic rocket, which I do discuss at some length in my book.

        There are two plausible ways to get to velocities v > .5c. The first I outlined above is the photon sail. A large Fresnel lens that collimates solar light onto a disk shaped sail craft could propel it to around .5c. Another approach would be to send nanoprobes to other stars. These could be sent to other star systems with an electromagnetic gun, similar to a particle accelerator, which would accelerate these nanoprobes to semirelativistic velocities. So we might imagine sending millions of these to another star. The trick there is to get these to attenuate their velocity upon approaching another star. From there a few of these probes might attach to an asteroid or some small body and begin to build up a system capable of exploration of the star system.

        Impacts with micrometeoroids present a problem. Even a microgram object would generate a lot of energy on impact. With the solar sail the thin material would permit this energy to not be absorbed much, as these impacts would leave perforations that would be below a fault tolerance. The actual spacecraft controlling the sail would be best configured into a bullet or needle shape to mitigate possible direct impacts.


      2. Peter Hamilton has his many-generation ships combine shields, having the mag field pushing a plasma in front. Dunno how much mass that requires, in principle you just need enough to incinerate frequent smaller impactors and can replace losses as you go. (The larger impactors have several options.)

    2. In my book I explore some of these issues, and generally I do think a star within 25 light years can be probed. However, you need to get to low gamma velocities. For v = .5c the relativistic gamma factor 1/sqrt{1 – (v/c)^2} is 1.154, and for gamma factor of 1.5 the velocity is .745c. These are velocities obtainable with a photon sail system. I work out the acceleration rates with time for this, and this is easily obtainable. The photons can be directed at the sail craft with a large Fresnel lens in space. Decelleration can be worked by having a large annular section of the sail detach and bounce photons to the remaining sail craft.

      If the average velocity to Gliese were .7c it means a probe could be there to explore the system in 28.6 years. That is about the same time of Voyager mission. Now remember, the probe has to send the information back at light speed, so there is an additional 20 years to receive anything. So that is 48.6 years or more. This is not an entirely unreasonable time frame. Time frames of 500 years and the like run into troubles with the fact that nation states, empires and civilizations historically do not last much longer than that.


  10. There are technologies that can be developed to mitigate impact damage. If I recall, we discussed this on another article. A combination of strong magnetic fields and a very thick and slender cone shaped nose on the front of the craft should mitigate interstellar damage to the craft. Don’t forget the command and control systems would likely have to be very autonomous, mission commands from Earth would take 20 years to reach the probe. An artificial A.I capable of conducting it’s own research and target selection independent of Earth control is likely needed. Self diagnostic and sophisticated self repair robotics/backup systems is essential. Currently, nothing like this exists.

    I wish your book was cheaper LC. I would very much like to read it. I am on a student budget however.

  11. Ha ha. The poster could well be from the school where I work. The sentence construction and use of ‘wuz’/’was’ for ‘were’ is very typical of Hull as is the spelling. Around three years ago a girl taking her GCSE [year 11] English exam wrote the whole of the paper in text-speak. Thankfully her paper was binned.

  12. I agree with the statement from William 928 that if Gliese 581d is suspected to be tidally locked, much like Mercury or Venus is in our own solar system, there will be no plate tectonics, no geological activity of mixing rock(solid planet) liquid(water,etc) and gas or atmosphere(carbon dioxide,water, methane hydrogen sulfide).We need this crust-liquid gas interaction to create balance. If the planets are that close to their suns, they might all be like the proximity of Io to Jupiter, that is liquid fire and hell. I do not give tidally locked planets much of a chance. I think we need to look at planets further out that are not tidally locked and a lot cooler. Heat breaks chemical bonds. If we are going to have complex life, cool might be a good idea.

    I understand why everybody is looking at these inner planetary systems, because they are the only ones we can physically see as the cross the star’s disc every few days, weeks or months. It makes no sense to wait 3-5 years for an outer planet to cross. Who would pay the research grant for that length of time for a temporary transit?

    Is there life on Ceres, much closer to home? It is in our own solar system and planet “number 5” and we cannot even tell if life is present or this will be our next home. We do not even have a good photo of it or whether it has an atmosphere and what that atmosphere is made of. Hopefully Dawn will bring us answers by 2015. I expect our first life in our solar system, away from Earth to be found here. Exciting times ahead, close to home.
    Chris Landau

    1. I agree that geology could be very different. Tectonic plate structure does seem to require oceans. Tectonic structure is involved with the carbon cycle, so it is an open question whether life, or certainly complex life, could exist on a planet without a carbon cycle.


  13. Mercury is not tidally locked. It is locked into a 3:2 rotational orbital resonance.

  14. Mercury is not tidally locked. It is locked into a 3:2 rotational orbital resonance.

Comments are closed.