Astrogator's Logs

New Words, New Worlds
Artist, Heather Oliver             

Once Again with Feeling: The Planets of Gliese 581

Gliese 581 may be small as stars go, but it looms huge in the vision field of planetfinders.  As of yesterday, measurements indicate the system has six planets of which three are Earth-size and -type, within the star’s habitable zone, with stable, near-circular orbits.

The Gliese 581 system has a persistent will-o-the-wisp quality.  Almost each of its planets (c, d, e and now g) has been pronounced in turn to pass the Goldilocks test, only to have expectations shrink when the data get analyzed further.  The first frisson of excitement arose when 581c was determined to be Earth-type, which quickened the usual speculations: atmosphere? water? life?  We don’t know yet and our current instruments cannot detect biosignatures at that distance (short of an unencrypted request for more Chuck Berry).  But there are some things we do know.

Gliese 581 is a red dwarf, a BY Draconis variable.  This makes it long-lived; on the minus side, it may produce flares and is known to emit X-rays.  Planets in its habitable zone are so close to it that they are tidally locked, always presenting the same face to their star.  The temperature differentials resulting from the lock imply hurricane-force winds and tsunami-like tides.  Gliese 581g, like 581c, is large enough to retain an atmosphere; the hope is that, unlike 581c or Venus, its specific circumstances have not resulted in a runaway greenhouse effect.

The real paradigm shift is the discovery that this solar system has many earth-size rocky planets, in contrast to the hot-Jupiter/hot-Neptune preponderance in most others.  The second enticing attribute of Gliese 581 is its relative closeness — a distance of merely 20 light years.  It is still millennia away by our present propulsion systems.  But I nurse the dream that if we see anything remotely resembling a biosignature, we will strive to reach it.  In the meantime, I suggest we give it a name that fires the imagination.  Perhaps Yemanjá, the Yoruba great orisha of the waters, in the hope that the sympathetic magic of the name will work.  Perhaps Kokopelli, the trickster piper of the American Southwest cultures, who may entice us thither.  I will conclude with the final words of my first article on Gliese 581:

“Whether Gliese 581c [g] is so hospitable that we could live there or so hostile that we could only visit it vicariously through robotic orbiters and rovers, if it harbors life — even bacterial life, often mistakenly labeled “simple” — the impact of such a discovery will exceed that of most other discoveries combined. Unless supremely advanced Kardashev III level aliens seeded the galaxy like the Hainish in Ursula Le Guin’s Ekumen, this life will be an independent genesis, enabling biologists to define which requirements for life are universal and which are parochial.

At this point, we cannot determine if Gliese 581c [g] has an atmosphere, let alone life signatures. If it has non-technological life, without a doubt it will be so different that we may not recognize it. Nor is it a given, despite our fond dreaming in science fiction, that we will be able to communicate with it if it is sentient. In practical terms, a second life sample may exist much closer to home — on Mars, Europa, Titan or Enceladus. But those who are enthusiastic about this discovery articulate something beyond its potential seismic impact on biology and culture: the desire of humanity for companions among the sea of stars, a potent myth and an equally potent engine for exploration.”

Images: Top, comparison of the Sun and Gliese 581 habitable zones (the diagram is by Franck Selsis, Univ. of Bordeaux; the image of 581g was originally created for 581c by Ginny Keller); bottom, Kokopelli playing his flute.

Note: This article has been reprinted on Huffington Post.

52 Responses to “Once Again with Feeling: The Planets of Gliese 581”

  1. Rose Lemberg says:

    Thank you! If nothing else, this suggests that Earth-like planets are not a rarity in the universe, which opens up all kinds of possibilities!

  2. Athena says:

    I’m happy you enjoyed the article, Rose! And you’re exactly right — with each discovery of this kind, the possible outcomes increase, including the “inhabited” one. I call it the asymptotic approach!

  3. andy says:

    The variable classification of the star seems to be erroneous: recent results show it to be pretty stable, not what you’d expect of a BY Draconis star.

    It is interesting that this system has 3 planets located very close to the habitable zone. Often popular science articles make a big deal about the narrow width of red dwarf habitable zones, which is usually stated to mean it is unlikely that a planet is going to end up at the right distance for liquid water. Of course, on a logarithmic distance scale, the red dwarf habitable zone is not so puny, and it seems that, as is often the case in nature, the logarithmic scale is what matters when dealing with the distribution of planetary orbits.

  4. ZarPaulus says:

    I’m wondering if “g” might be suitable for human colonization, though I suspect it would require some modification.

  5. Athena says:

    Andy — if so, the odds improve even more. Red dwarf habitable zones are considered narrow because they’re always compared with F, G or K stars. In practical terms, I suspect they’re wide enough to accommodate a couple of planets.

    Paul — I wish we knew! *impatient sigh*

  6. Walden2 says:

    And in nineteen years time if anyone is there and they have radio astronomy they’ll get a whole bunch of messages from the talking primates with car keys living on Sol 3:

    While it is of course very exciting to think that an Earthlike world is out there for real, there will probably not be any place exactly like Earth, meaning we will have to modify it for humans to live there without spacesuits and pressure domes. And then that brings up the tricky bit about what happens to any life that already lives there.

    And what if someone out there has found Earth thinks hey, with a few modifications here and there, our planet would make a nice home for them?

    Most people now are too caught up in their issues here to worry about these things, but in the not too distant future they could be the most pressing items of our survival and of life in the rest of the galaxy: Who gets to own and live where?

  7. Athena says:

    That’s right, we sent a signal to Gliese 581. As you already know, Larry, I agree with you about the ethical dilemmas of “settling” a planet with its own native life, as I discussed in my Making Aliens series. Our previous history with of terrestrial encounters, with both other cultures and different biosystems, does not bode well.

  8. Neo says:

    My mom liked the news very much… 🙂


  9. […] This article is also at the author’s blog, with a neat diagram showing a comparison between the habitable zones of our Sun and Gliese […]

  10. […] This article is also at the author’s blog, with a neat diagram showing a comparison between the habitable zones of our Sun and Gliese […]

  11. Walden2 says:

    According to this APOD post, one of the heads of the team that found this exoplanet unofficially calls it Zarmina’s World, after his wife. Certainly has the aura of exoticness about it:

    I wonder what the inhabitants of that planet call their world? :^)

  12. Athena says:

    Yes, I saw that! Although the gesture is romantic, it also reminds me of Titan A. E. where they jokingly call their new home planet Bob. I wonder what the native name for it is, also… (*smile*)

  13. Ginny Keller says:

    Hi – I was wondering where that solar system diagram came from? A picture I created for Gliese 581c is being used for 581g 🙂 I’m happy to see it used – just trying to track down the source for attribution 😉

  14. Athena says:

    I’m glad you got in touch, Ginny! I’ve been trying to track both you and the creator of the habitable zone of Gliese 581 for proper attribution. I put your globe of 581c as 581g because its markings make it look Earth-like. I updated the post with your name and a link to your art site.

  15. Walden2 says:

    Steve Vogt responds to his critics about saying that exoplanet Zarmina (a.k.a. Gliese 581g) has life on it without having actual scientific proof of such life:

  16. […] This article is also at the author’s blog, with a neat diagram showing a comparison between the habitable zones of our Sun and Gliese […]

  17. Ginny Keller says:

    I’m happy I could contribute 🙂 Deeply fascinating stuff this is! Cheers 🙂

  18. Athena says:

    Ginny, you are right, the stuff is absolutely riveting. I hope that you continue depicting possible earths!

    Larry, the io9 post you linked to used the modified diagram that I created using Franck Selsis’ habitable zone and Ginny Keller’s picture for 581c (see the comments just above — she originally created it for 581c, when the scientific community thought it might be Earth-like; when I wrote this post, the news was so recent that nobody had a depiction of 581g).

    As for Vogt’s speculations about life, he’s as right or wrong as anyone else, given our total lack of information in that domain. However, the logic that equates the likelihood of the origin of life to flipping coins is incorrect. Life processes are not stochastic, and there are conditions that favor their development. If Gliese 581g fulfills those, the odds of life on it increase significantly.

  19. Asakiyume says:

    (short of an unencrypted request for more Chuck Berry) ^_^ Now I wonder how the world would react if that *were* our first contact.

    I like your suggestion to choose a name with sympathetic magic to it! It didn’t work so well with our turbulent Pacific Ocean, but I’ve found it worked well with my own children (well enough that I’d counsel anyone against naming a child Tempesta or Deceptus, at least). And a trickster name sounds good too, someone who will lead us, piping merrily, to a new destination.

    Very nice, too, your reminder that bacterial life is not “simple.”

  20. Asakiyume says:

    (I’ve now added your blog as a feed on my LJ–now I’ll never miss a post)

  21. Athena says:

    Names shape us — after all, naming is the first function of language and imbues what is named with all kinds of significance and connotations: Uluru versus Ayers, Denali versus McKinley, Athena versus Mary (*smile*). Too, Tricksters and Pied Pipers tend to be harbingers of change: Lilith, Lucifer, Prometheus, Loki, Coyote/Raven, the Monkey King.

    I often wonder what life looked like before bacteria. By the time bacteria evolved, things were already incredibly complex, and the machinery of life was fully in place.

  22. Walden2 says:

    Speaking of celestial names, here is an article on Arabic star names:

  23. Athena says:

    I already knew the meaning of several of these (Algol, Deneb, Altair) — but it’s amusing to learn how many bright stars are Arabic variations on body parts, particularly “tail” (*laughs*). Which takes us back to the importance of naming!

  24. Walden2 says:

    Christianity and Extraterrestrial Life: Are the Gliesans Going to Hell?

    by Karl Giberson, Ph.D.BioLogos Foundation

    Posted: October 10, 2010 09:00 AM

    Full article here:

  25. Athena says:

    BioLogos is an Evangelical Christian foundation. So this is really a conversation between fundamentalists. The article is essentially a publicity stunt for the creationist museum and its founder.

  26. Walden2 says:

    I did not know that, sorry. Why did the Huffington Post post it then?

  27. Athena says:

    HuffPo posts anything that will attract attention, including articles from such “deep thinkers” as Deepak Chopra and Robert Lanza. You may have noticed that it has a section for religion, but not one for science (it has one for “tech” which almost exclusively discusses Internet meta-issues).

  28. Walden2 says:

    Oct 12, 2010

    Buzz About Gliese 581g: Doubts of Its Existence; Aliens Signals Detected

    by Nancy Atkinson

    Ever since the announcement of the discovery of exoplanet Gliese 581g, there has been a buzz in the news, on websites, Twitter – pretty much everywhere, about the first potentially habitable extrasolar planet. But the past couple of days there has been a different sort of buzz about this distant world.

    Two stories have surfaced and they both can’t be true. The first one is fairly off the deep end: an astrophysicist from Australia claims that while doing a SETI search two years ago, he picked up a “suspicious signal” from the vicinity of the Gliese 581 system, and a couple of websites have connected some dots between that signal and a potentially habitable Gliese 581g.

    The second one is more sobering. At an International Astronomical Union meeting this week, other astronomers have raised doubts whether Gliese 581g actually exists.

    Full article here:

  29. Athena says:

    The serious problem with these detections is that they rely on perturbations of the star’s orbit or spectal lines — and the fluctuations are as high as the “event” measurements. The smaller and/or more distant the planet is, the worse the problem gets. The only real solution is direct optical observation. This means bigger Hubble-like telescopes or targeted robotic probes. Which is the hopeful take on the news: more observation, not less… and constant self-correction and refining of the data.

    As for the purported signal, how good is the data? Is it as good as the Wow one? SETI has made a decision to look for repeated signals because that increases reliability. However, signals from sentient sources need not be repeated.

  30. Walden2 says:

    The fact that the guy who is claiming to detect these signals won’t share them is highly suspicious to put it mildly. Has anyone else performed SETI on that system for that matter?

    Honestly I doubt anything is signalling us from the Gliese 581 system, but if someone is going to make such a claim and they also claim to be real scientists, then they will behave like a scientist should.

  31. Walden2 says:

    To further add, that someone is detecting signals from Gliese 581 of all systems is probably in the same category that only the biggest and brightest comets get to be followed by alien spaceships and such:

    To paraphrase a famous film quote, show us the data!

  32. Athena says:

    Are you referring to Broken Glass, Larry? That was a near-perfect film.

  33. andy says:

    I already knew the meaning of several of these (Algol, Deneb, Altair) — but it’s amusing to learn how many bright stars are Arabic variations on body parts, particularly “tail” (*laughs*). Which takes us back to the importance of naming!

    Definitely quite amusing when people complain about the horrifying numeric designations the modern sky surveys use, which are essentially the designation of the survey followed by some representation of coordinates, when lots of those “poetic” names are basically just telling you which bit of the constellation the star represents. Calling stars by their position has a much longer tradition than is at first apparent!

  34. Walden2 says:

    No, I don’t know that film, Athena. I was referring to the Jerry MacGuire quote “Show me the money!”

  35. Athena says:

    I haven’t seen Jerry McGuire. The same quote is used in Broken Glass, to great effect.

  36. Walden2 says:

    Well, I think we both know what our next homework assignments are.

  37. Walden2 says:

    Update on Gliese 581d’s Habitability

    by Jon Voisey on May 6, 2011

    An artist’s impression of Gliese 581d, an exoplanet about 20.3 light-years away from Earth, in the constellation Libra.

    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.

    Full article here:

  38. Athena says:

    I’ll be happy when ONE of the Gliese 581 planets is certified as existing! If it’s also potentially habitable, I’ll be positively ecstatic…

  39. Walden2 says:

    Well at least we have some METI heading that way just in case. :^)

    Case builds for habitable alien planet

    Zina Deretsky, National Science Foundation

    The orbits of planets in the Gliese 581 system are compared to those of our own solar system. The Gliese 581 star has about 30 percent the mass of our sun, and the outermost planet is closer to its star than we are to the sun. Gliese 581d might be able to sustain liquid water on its surface.

    By John Roach

    The case is building about the habitability of a planet orbiting a red dwarf star about 20-light years away from Earth, according to a new climate modeling study.

    The planet, Gliese 581d, is one of a handful of planets orbiting the star Gliese 581. When it was discovered in 2007, astronomers thought it was likely too cold for liquid water, and thus life.

    The new study, accepted for publication in the Astrophysical Journal Letters, suggests high concentrations of carbon dioxide in its atmosphere could keep things warm enough for liquid water to be sustained at the surface.

    The finding falls on the heels of a similar atmospheric modeling studies published that have reached a similar conclusion.

    Full article here with a link to the AJL paper:

  40. Athena says:

    Yes, I saw that article. Models are all well and good — we need observational proof! Telescopes, probes — I can’t believe they defunded the Allen array when all this is at our doorstep.

  41. Walden2 says:

    Well the Green Bank Radio Observatory in West Virginia is now looking at some of the more or less promising candidates recently detected by Kepler, but to be honest it seems more like a token and “safe” effort.

    Virtually none of the alien worlds Kepler has found, bountiful as they have been over all previous exoplanet discoveries, are actually close to anything Earthlike or even near in size to our planet. Obviously I cannot say definitively whether there is life on those places or not of any kind, but it seems questionable that the relative handful of worlds which Kepler detected would also just happen to have ETI that possess radio technology and are signalling us.

    Maybe there is a spaceship or two from some other solar system ala Star Trek exploring one of those systems and they decided to do a little METI while there, but I think you see what I mean.

    Mainstream SETI needs to focus on other places in addition to Sol-type systems such as infrared sources out on the galactic fringes where it is very cold and in the comet and planetoid belts of our Sol system. They also need to expand their search range beyond radio and optical, though I know the latter has only recently just gotten into vogue after years of unwarranted rejection by the mainstream SETI community. Just ask Dr. Staurt A. Kingsley what he had to go through to get Optical SETI accepted by the radio guys, or see his Web site at

    Between all this and the fact that we are really just fancy animals, no wonder we haven’t found other minds yet or why they aren’t saying Hello to us.

  42. Athena says:

    I agree that focusing on the Kepler planets is a holding action, but at least it will prevent SETI from being seen as “idle pursuits of airheads” — a very concrete danger, as the Proxmire award demonstrated. At this point, all space exploration efforts are so woefully underfunded that any actions and results are miracles.

    I cannot believe I’m making such statements at this place and time of our species.

  43. Walden2 says:

    Nearby “earth-like” planet: not so much

    There’s some chatter on the web right now over a new scientific paper about a nearby exoplanet, and what I’m seeing are people speculating that it might be earth-like. Technology Review even titled their article “Astronomers Discover Habitable ExoEarth Orbiting Binary Star”.

    The problem with that is that the planet’s not terribly earth-like, and it may not be habitable*.

    So what’s the deal? I read the journal article (PDF), and this really is a good story, just not the one I’m seeing the chatter about.

    55 Cancri is a nearby binary star at a distance of about 40 light years. One star is a dinky red dwarf, and the other is a fairly Sun-like star, though somewhat smaller and cooler. It’s also much older, roughly 10 billion years old, more than twice the age of the Sun. It’s actually at the point where it’s starting to evolve into a red giant, and is called a sub-giant.

    Back in 2007 it was announced that at least five planets orbit the bigger of the two stars (called 55 Cancri A; confusingly the red dwarf is 55 Cancri B (note the capital letter), while the planets are called b-f (lower case)). They range in mass from 0.026 to 3.84 times that of Jupiter (8.3 to 1200 times the mass of the Earth). 55 Cancri e is the lowest mass of these, but is extremely dense and hot, so not at all earth-like.

    55 Cancri f is the interesting planet, though. The astronomers in question observed the star using an interferometer, allowing extremely precise measurements of the star’s size, which in turn yielded very accurate numbers for its temperature and mass. All these together can be used to figure out its “habitable zone”, the region around it where an orbiting planet would have liquid water on its surface.

    Now right away, I’ll say that finding the HZ (as we in the know call it) is not really straightforward. For example, a planet that has a thick atmosphere can be farther from its star and still have water due to the greenhouse effect; in fact, without air the average surface temperature of the Earth would be below freezing! And the greenhouse effect depends on what’s in the atmosphere, its density, and so on. So I am wary of any declarations of planets being habitable based on this alone.

    Full article here:

  44. Athena says:

    I had heard the buzz about this system as well, and like you I’m withholding judgment (and wild dancing) until we know more.

  45. Walden2 says:

    One-Third of Sun-Like Stars Have Earth-Like Planets In Habitable Zone

    Astronomers have calculated the likelihood of finding Earth-like planets around other stars using the latest data from the Kepler mission.

    kfc 09/27/2011

    The Kepler orbiting observatory is specifically designed to find Earth-like planets around nearby stars.

    Earlier this year, the Kepler team released the mission’s first 136 days of data and it has turned out to be a veritable jackpot. In that time Kepler looked at some 150,000 target stars and found evidence for 1,235 potential exoplanets. That’s quite a haul.

    Since then, most of the work on this database has been to identify the characteristics of all these exoplanets. But such a large dataset also allows for statistical analyses too, from which various projections can be made.

    Today, Wesley Traub at the California Institute of Technology in Pasadena, reveals the results of just such a study. Traub has looked only at the stars that are most similar to the Sun, namely those with the classification F, G or K and worked out often various types of planets occur.

    The results are straightforward to state. Traub says that mid-size planets are just as likely to be found around faint stars and bright ones. By contrast, far fewer small planets show up around faint stars. That’s almost certainly because small planets are more difficult for Kepler to see.

    It’s also easier for Kepler to see planets that are closer to their stars because it looks for the tiny changes in brightness that these transits cause. That’s why almost a third of all Kepler’s detections orbit their star in less than 42 days. For the most part, these planets orbit too closely to be in the habitable zone.

    What interests most astronomers is how many exoplanets orbit at a greater distance, inside the habitable zone. Most of these planets are too far away from their stars to have been picked up by Kepler yet. But Traub says his data analysis provides a way to work out how many their ought to be.

    That’s because he’s found a power law that describes how the number of stars with a given orbital period. So all he has to do is assume a longer orbital period equivalent to being in the habitable zone to work out how many planets there ought to be at this distance.

    Here’s the answer: “About one-third of FGK stars are predicted to have at least one terrestrial, habitable-zone planet,” he says.

    So by this measure, there are plenty of other Earths out there.

    Ref: Terrestrial, Habitable-Zone Exoplanet Frequency from Kepler

  46. Walden2 says:

    I was ready to dismiss this piece until I read who reported this. Does not mean it is the real deal, but at least he is not some unknown crank or that this is an outright hoax.

    Does ET live on Goldilocks planet? How scientists spotted ‘mysterious pulse of light’ from direction of newly-discovered ‘2nd Earth’ two years ago By Niall Firth

    Last updated at 12:45 PM on 17th August 2011

    Read more:

  47. Athena says:

    This sounds very similar to the WOW signal. But if there is a second independent confirmation, it may motivate us to send ships to the Gliese system. At the same time, Gliese 581g is still inferred — and its existence depends on the assumptions of this inference.

  48. Walden2 says:

    Looks like Gliese 581 just got knocked off the top podium:

    Of course it won’t be long before Kepler-22b ends up with Gliese 581, but that is a good thing for scientific knowledge.

  49. Athena says:

    Yes, I’ve been tracking the stories. I may say something about it, if this lingering cold will allow me coherent thinking. The asymptotic approach to the Drake equation… if only we had stronger telescopes in orbit!

  50. Walden2 says:

    No big surprise here – SETI detects no radio signals from Gliese 581 system: