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Gl 581g: Rocky and Potentially Habitable

What exactly does the word ‘habitable’ mean? The question comes to mind because of two things, the first being the media buzz over Gliese 581g, now widely described as the first potentially habitable planet we’ve found. The second is Paul Davies’ presentation yesterday at the International Astronautical Congress in Prague, where Davies was careful to differentiate between ‘habitable’ and ‘inhabited.’ More on the latter in a moment. Let’s look first at this outstanding find, two new planets in the Gliese 581 system discovered through the unflagging efforts of the Lick-Carnegie team.

A World in the Zone?

The beauty of Gl 581, of course, is not only that it has yielded a storehouse of planets (six known at present), but that these worlds are on nearly circular orbits, and several have caught our eye re habitability before. The current buzz seems a bit tamer than the one that greeted the announcement of Gl 581c, at the time thought to be capable of sustaining liquid water on its surface, although later research has shown that the planet is much more likely to be a Venus-like heat trap. Gl 581d, too, has its supporters, who argue that given the right atmospheric composition, temperatures there might be sufficient to sustain life.

But Gl 581g looks to be the most promising of the bunch, with a mass between three and four times that of Earth, a rocky world with enough gravity to hang onto an atmosphere and surface temperatures that average between -31 and -12 degrees Celsius. That’s cold, of course, but actual temperatures here are going to depend on where you happen to be, the planet being tidally locked to its star. I like what Stephen Vogt (UC-Santa Cruz) said at the press conference announcing the finding. Vogt talks about ‘eco-longitudes,’ meaning that on a tidally locked world like this, there will be temperature zones that follow the longitudes, from very hot at the center of the star-facing side to freezing on the dark side. Let me quote him briefly:

“If you are in the most comfortable place on this planet, which would be on the terminator, you would see the star sitting on the horizon. an eternal sunrise or sunset, depending on whether you are an optimist or a pessimist. Over billions of years, there would be stable zones where the ecosystem stays at the same temperature. You have ‘eco-longitudes,’ so that if you have evolved to like hot zones, you move a bit toward the star side, and if you like cold zones, you move toward the shadow side. And it stays like that more or less forever, so there are a lot of different niches for different kinds of life to evolve.”

The ‘goldilocks’ metaphor is being used all over the place to describe this planet’s orbital placement, a comparison Vogt was quick to exploit (this from a UC-Santa Cruz news release):

“We had planets on both sides of the habitable zone–one too hot and one too cold–and now we have one in the middle that’s just right… Any emerging life forms would have a wide range of stable climates to choose from and to evolve around, depending on their longitude.”

Tidal Lock and Open Questions

I’ll never get over the fascination of places like this, where the sun never moves in the sky and patterns of light and shadow are permanent, so that to move through what we consider a day-like cycle of light and dark would require physically moving along the surface of the planet. The terminator region between dark and light may be the most habitable region, though our modeling of atmospheres on such worlds is an ongoing thing, and it was only in the late 1990s that we began to realize, thanks to work by Manoj Joshi, Robert Haberle and team at NASA Ames, that a tidally locked planet might sustain regions stable enough to support life. Other questions, particularly that of solar flares on frequently active M-dwarfs, remain open.

Vogt talks about 238 observations with a precision of 1.6 meters per second being required for the radial velocity observations that found this world, and in the news conference, he pulled out a telling analogy to explain their precision. Use exquisitely sensitive calipers to measure a 6-inch ruler. Now stand the same ruler up on its end and measure it again. It will be infinitesimally shorter because it shrinks under its own weight, the effect of gravity. That tiniest of all changes is about on the order needed to find a Gl 581g amongst the data. It’s superb work, combining HIRES spectrometer (which Vogt designed) observations with published data from the Geneva group, and it is the result of fully eleven years of study of this interesting star.

The Nature of Habitability

But let’s get back to that question about habitability. First, Vogt is of the opinion that finding GL 581g this early in the planet hunt (with some 500 exoplanets now found) is a telling feat:

“If these [habitable worlds] are rare, we shouldn’t have found one so quickly and so nearby. The number of systems with potentially habitable planets is probably on the order of 10 or 20 percent, and when you multiply that by the hundreds of billions of stars in the Milky Way, that’s a large number. There could be tens of billions of these systems in our galaxy.”

Encouraging indeed. But I’m also reminded of Paul Davies’ comment yesterday in Prague. Davies was addressing the change in opinion in the scientific community, which has in the past fifty years moved to support the idea of extraterrestrial life. In the paper on which his presentation was based, Davies writes “…to profess belief in extraterrestrial life of any sort, let alone intelligent life, in the 1960s and 1970s, was tantamount to scientific suicide. One might as well have expressed a belief in fairies.” But all that has changed with new discoveries, leaving many scientists convinced of life’s ubiquity. Davies takes a more cautious view.

We might, for example, call a planet ‘habitable’ because it can support liquid water at the surface. But is this enough? Again from the Davies paper (and all the italics are his):

Water does in fact seem to be abundant in the solar system and beyond, so (it is reasoned) life should also be abundant. Unfortunately this simplistic reasoning confuses a necessary with a sufficient condition. To be sure, liquid water is necessary for life (at least as we know it), but it is far from sufficient. The reason life on Earth inhabits almost all aqueous niches is because Earth has a contiguous biosphere, and life has invaded those niches; it has not arisen there de novo.

Davies is concerned less about life’s ability to adapt to extreme conditions than about the likelihood of its formation in the first place. Indeed, this is the question that so confounds our pulling meaningful information from the Drake Equation, in his view. He goes on:

Another reason given for the current optimism about life beyond Earth is the dawning recognition that life can survive in a much wider range of physical conditions than was recognized hitherto, opening up the prospect for life on Mars, for example, and generally extending the definition of what constitutes an “earthlike” planet. But this at most amounts to a factor of two or three in favor of the odds for life. Set against that is the exponentially small probability that any given complex molecule will form by random assembly from a soup of building blocks. In short, habitability does not mean inhabited. It is natural that we should concentrate on the habitable planets in our search for life – by the “keys under the lamppost” principle –but at this stage we cannot put any level of confidence – none at all – on whether such a search will prove successful.

Cause to Celebrate Nonetheless

So there you are, a cautionary note in an otherwise celebratory morning (and Davies, of course, wasn’t aware of the Gl 581g news when he wrote this). But even as I understand Davies’ position, I have to say that my own mood is much more upbeat. We have much to learn, but what an achievement this discovery is, showing our capability of finding planets of near-Earth mass, planets likely to have atmospheres, and surface conditions that could sustain water in liquid form. Whatever really exists on Gl 581g, it’s a fact that this discovery points toward near-term discoveries of planets much more like our own, around G and K stars at distances where tidal lock is not an issue. We still have no ‘second Earth’ but it’s only a matter of years (perhaps even months) before we find one.

And let’s not forget the second planet in the discovery announcement. No question of habitability here, but we should note the existence of Gl 581f, at a minimum-mass seven times that of the Earth, and orbiting at 0.758 AU with a period of 433 days. Gl 581g is going to get the lion’s share of attention, but we’re moving into the era of characterizing entire planetary systems and that in itself is worthy of celebration. It will ultimately teach us much about planetary formation and help us refine the strategies we need to bag that first unquestionably ‘Earth-like’ planet.

The paper is Vogt, Butler et al., “The Lick-Carnegie Exoplanet Survey: A 3.1 M_Earth Planet in the Habitable Zone of the Nearby M3V Star Gliese 581,” accepted by The Astrophysical Journal and available as a preprint.


Comments on this entry are closed.

  • philw1776 September 30, 2010, 10:52

    The planet might not be tidal locked. Other massive neighbors are nearby so it could have a rotational resonance. HUGE tides hauling any putative oceans around scouring the planet on a weekly basis.

    Davies is quite right. After over half a century of space exploration we do not have one scintilla of scientific evidence that falsifies the hypothethis that the 1st life on Earth was a once in a universe or other low probability as many biologists (not astronemers) speculate. An advanced space spectrometer would have a shot at such falsification. I leave out the possibility of life elsewhere in our own solar system as potentially being the residue of Earth pollution, or possibly the reverse. :)

  • stephen September 30, 2010, 10:53

    Another interesting possibility is a planet with a day longer than its year–maybe it rotates one time for each thousand revolutions around its sun. Or it might take even longer.

  • djlactin September 30, 2010, 11:11

    (1) Why do we always assume that a planet that close to the primary will be tidally locked? The only planet (Mercury) in our solar system that ‘should’ be tidally locked is not (3 rotations/2 revolutions). Certainly other resonances are possible?
    (2) Wouldn’t it be cool to be a space-faring species in a stellar system in which the nearest neighbor is a (relatively) trivial distance away?
    (3) Couple thought 2 with a multiple star-system, with the nearest neighbor less than a light year away. Interstellar travel would be merely another step.

  • bigdan201 September 30, 2010, 11:41

    Truly exciting news.

    I’m looking forward to more information about this planet, especially the equatorial surface gravity. Also, a chart I found on the wikipedia article seems to indicate that planet d would cross planet g’s orbit – is this correct? If so, is this a stable configuration?

    In any case, this is a huge development for the possibilities of exobiology, as well as eventual human colonization – not just there, but also on other earth-like exoplanets, which very likely exist given this discovery.

  • Tulse September 30, 2010, 11:48

    Are there any reasonably near-term options for determining whether Gl 581g has an atmosphere, and if so, whether it has signs of biological activity? Since it was discovered via the radial velocity method, I presume that means we don’t yet have any transit detection, and so can’t do spectrographic studies — would that be a possibility in the future, or is it in the wrong plane for seeing transits? (And can one potentially use starlight from other stars as the occluded light, to get spectrographic data from non-transiting planets?)

  • Istvan September 30, 2010, 12:04

    “it was only in the late 1990s that we began to realize … that a tidally locked planet might sustain regions stable enough to support life.”

    Well, perhaps we began to substantiate this through analyses at that time, but these kinds of environments were certainly fodder for SF tales in the 50’s, and likely before. I remember a planet referred to as a “ribbon world”, describing its habitable zone, in vintage fiction by Asimov, though I cannot just now name the world, or the specific story, from memory.

    Gliese 581 is obviously a fascinating target, and has been even before these new reports. It is a pity it’s not among our nearest neighbors, or I suspect our discussions of precursor interstellar missions would be in the process of growing less academic.

    A topic that might be of interest, if I might diffidently make a suggestion to those with hopefully more time and certainly more knowledge already at hand, might be to provide a discussion of the known characteristics of our neighboring systems, the requirements of our transit, radial velocity, and other observational techniques, and why current work is providing a bounty of data on some systems, while we yet know little about many other, nearer ones. Such might prove to be the core of an article with wider potential audience than just these forums and this site.

    I’d love to do the research myself and try my hand at some professional science writing, since I think this would be a broadly appealing article, but I’m unfortunately or fortunately already very employed at rather more than the normal number of hours per week! Of course, if such a summary article already exists, I’d be thrilled to find a link.

  • Carl Keller September 30, 2010, 12:44

    This is actually front end Yahoo news http://news.yahoo.com/s/ap/20100929/ap_on_sc/us_sci_new_earths

    Arthur Clarke had a very good story “The Wall of Darkness”. It was about a world locked in perpetual day, with a civilization inhabiting the ring from the terminator to the edge of a torrid zone.

  • Tulse September 30, 2010, 14:21

    “A topic that might be of interest […] might be to provide a discussion of the known characteristics of our neighboring systems, the requirements of our transit, radial velocity, and other observational techniques, and why current work is providing a bounty of data on some systems, while we yet know little about many other, nearer ones.”

    On a related basis, I can heartily recommend the Visual Exoplanet Catalogue:


    and even more heartily recommend the iPhone/iPad app based on it. The Catalogue is a database of all identified planets, including their star, method of discovery, mass, rotational period, distance from its star, the star’s habitable zone, the star’s metallicity, etc. etc. etc. It’s a great resource.

  • Thomas Hair September 30, 2010, 14:37

    Stephen Vogt is a planet hunter extraordinaire, but he ought to leave statements like this to the National Enquirer…

    “Personally, given the ubiquity and propensity of life to flourish wherever it can, I would say, my own personal feeling is that the chances of life on this planet are 100 percent,” said Steven Vogt, a professor of astronomy and astrophysics at the University of California, Santa Cruz, during a press briefing today.

    As Paul Davies points out the ubiquity argument is nonsense in a contiguous environment and beyond that no one knows how rare biogenesis is…it’s a big step from amino acids to the simplest life. I just cannot understand what possesses otherwise brilliant people to make idiotic statements like this.

  • Carl Keller September 30, 2010, 14:55

    I knew it wouldn’t take long for some interpretations of this world to hit the web: http://io9.com/5652307/what-a-colony-might-look-like-on-gloaming-the-newly+discovered-second-earth

    The article goes on:
    ‘Officially known as Gliese 581g, we’ve dubbed the newly-discovered planet Gloaming, a word that means “twilight.”‘

    I believe the IAU has not recognized the names Bellerophon and Methuselah yet. Gloaming is submitted in short order with no debate?

  • Athena Andreadis September 30, 2010, 15:36

    I wrote earlier about Gliese 581c, and now about 581g. Gloaming is generic and flouts tradition. My naming suggestions are different, for reasons I explain in the article.

    Once Again with Feeling: Gliese 581

  • Antonio September 30, 2010, 15:58

    Il Telescopio Spaziale “Spitzer”(o altri analoghi)potrebbero fare qualche rilevamento scientificamente interessante, sulla temperatura, e composizione chimica dell’atmosfera di questo pianeta?

    E poi, la temperatura del lato più caldo del pianeta, a quanto arriverebbe?

    Considerando che la temperatura media è al di sotto del punto dove l’acqua è allo stato liquido(ma poi bisogna vedere a quanto arriva la pressione atmosferica al suolo)non mi sembra che sia poi tanto abitabile…

    Comunque, è una scoperta davvero interessante…

    Saluti da Antonio.

  • Paul Gilster September 30, 2010, 16:28

    Antonio’s comment via Google Translate:

    The Space Telescope Spitzer “(or similar) could do some interesting scientific detection, temperature and chemical composition of the atmosphere of this planet?

    And then, the temperature of the hot side of the planet, it would arrive?

    Considering that the average temperature is below the point where water is liquid (but then you see what the air pressure reaches the ground) does not seem to be living that much …

    However, it is a really interesting …

    Greetings from Antonio.

  • stargazerdude September 30, 2010, 16:57

    This planet needs a name that will excite the imagination…

  • Carl Keller September 30, 2010, 18:06

    Hello, Athena. Your link, http://www.starshipnivan.com/blog/?p=3029 had the statements:

    “…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 like your name suggestions. The image of Kokopelli is frequently encountered and would resonate with people. Certainly more fitting than the fiction site’s poor idea.

    More discoveries are not far off with Kepler and the other dedicated programs designed to locate “Goldilocks” planets. The exoplanet count could reach four figures within a year or two, with more than a few of the sought-after terrestrial bodies in that number.

  • andy September 30, 2010, 18:37

    Rocky? Perhaps. Bear in mind it is located outside the orbit of a hot Neptune (Gliese 581b). The Neptune-mass planet had to have formed further out and migrated inwards, because there would not be enough material to form it in situ. This migration would have dragged ice-rich material from the outer system inwards, and thus the planet g would likely have formed with a much higher water content than the terrestrial planets in our solar system. The planet is therefore more likely to be an ocean world with a composition dominated by ices than a terrestrial planet like the Earth.

  • John Freeman September 30, 2010, 19:09

    “Gaiŭp mŭnya”, meaning ‘two’ in wotjoballuk aboriginal language- it seems appropriate given much of the dayside will be desert if it is tidally locked.

  • TK September 30, 2010, 19:46

    Thomas Hair :

    Although Vogt’s argument is weak I think it’s the kind of response to give to a paper like this one, it’ll make some people dream and there’ll be more people interested in the exo planet search so it’s all good.

    This new exoplanet is great news, I hope we’ll hear and read more and more often about earth like exoplanets in the near future.

  • Greg September 30, 2010, 20:46

    How about Primul? that’s Romanian for “the first one”

  • joseph September 30, 2010, 23:11

    I agree that the planet “G” may not be tidally locked but for a different cause. I note that in solar system 1 planet out of 8 has a massive satellite. Earth’s rotation rate has been profoundly slowed by the moon and by the same token IF our little Goldilocks world has a large satellite it would be tidally locked to ITs orbit, not the presence of the red star. Most likely there would be resonance effect between planet orbit, satellite orbit and planet rotation.
    Be we speculate. there is only a slim chance there is a large satellite.
    image if there were.. what a great set up to give birth to a species that could escape its planet of origin, traveling first to the moon and then to the outer planets, then to an oort cloud,,, and then to drift away dispersed on small dwarf planets… Oh ! wait! that is OUR fate.. we know We have a moon and nearby step stone world -Mars- .. then Callisto, then Triton.. then Pluto, Sedna and on an on…

  • Thomas Hair September 30, 2010, 23:14


    I do agree it’s all good with respect to this incredible find. My concern is when I see a serious scientist like Vogt make an outrageous and undefendable statement like “the chances of life on this planet are 100 percent”, I get images of Michio Kaku at a scifi convention asking people dressed like Klingons what they think of 581g and receiving blank stares while the Discovery Channel cameras soak it all in.

  • Thomas Hair September 30, 2010, 23:37

    One last comment TK…

    The scientific community should not lower the discourse on this issue as Vogt has done with his 100% comment. The question being asked is primal…are we alone. Almost everyone gets this and almost everyone thinks about this. From the average Joe to the hyper-educated many folks have a wunderlust for the cosmos. Oversimplification and ridiculous statements will just ensure that James Cameron will make a bunch of money off the ten sequels he has planned for Avatar.

  • Tom October 1, 2010, 0:11

    “Set against that is the exponentially small probability that any given complex molecule will form by random assembly from a soup of building blocks.”
    I have heard this type of arguement again and again since I can remember, but it is a coarse and ill-considered argument. I don’t think anyone expects life (here or anywhere else) to spontaneously appear, it much more likely evolved stage by stage from simple molecules all the way to whole cells. Just because we currently don’t know all the in-between stages is no reason to expect there weren’t any.
    The counter-argument is “we don’t believe it is possible for a molecule smaller than RNA to self-replicate, so nothing could evolve before this sprung into existence.”
    Which is wrong, you can still evolve more and more complex molecules without self-replication, for example a set of small molecules can each partially build each other in different specialist ways.
    Anyone who has looked at cellular automata can see how large objects can be built from simple rules, and so for me there is no big jump, no spark that needs igniting, no fortune, given enough time with the right environment large molecules will form which eventually evolve into life.

  • Iball October 1, 2010, 7:10

    How about Aurora? As in Aurora Aeturnus – the eternal sunrise.

  • Michael Spencer October 1, 2010, 7:49

    Surely Dr. Vogt’s exuberance is no more clearly demonstrated than his permissible ‘100%’ comment? It’s a touching, human, and forgivable moment. I for one want to see passion in scientists.

    Far more interesting is the analogy of a pencil shortening due to gravity. I am too far out of school to calculate that number–likely buried very deeply to the right of the decimal point beyond innumerable zeros. And if this analogy is more robust than his estimate of life’s probability, it’s a sweet measurement indeed.

  • Marc G Millis October 1, 2010, 7:58

    In case it has not yet been said, the star, Gliese 581, is about 20 light-years away. In terms of interstellar flight, that is relatively close!


  • Martin Alfredsson October 1, 2010, 12:44

    Interesting discussion about life.
    Our knowledge of life possibility is really limited. There could be millions of whalesized creatures floating in space in our own solar system and unless they fell down on inhabited parts of the earth we would no be able to find them.
    While I dont think space is full of whales what it means is that we are yet unable to see almost everything.
    I have no idea if there are any life in other parts of the solar system nor if there are life anywhere else, for all I know we might be unique or panspermia might spread life all the time.
    But what I know is that we dont have enough data to do anything else than speculate. Things like Drakes equations and panspermia are still speculative.
    We cannot use use Occams Razor when we dont have enough data.

  • Ronald October 1, 2010, 13:45

    Although Vogt’s statement may be overly optimistic to the extreme, undoubtedly and understandably inspired by enthousiasm, I find Davies’ statement about the unlikelihood of complex molecules way too gloomy (‘Set against that is the exponentially small probability that any given complex molecule will form by random assembly from a soup of building blocks.’). And, in fact, plain wrong.
    Complex, even self-replicating molecules of several hundred C atoms length do indeed originate spontaneously and all the time.
    A statement like this almost feels like creationism, the well-known antiquated mantra that the chance of a particular complex molecule arising purely by coincidence is vanishingly small. Nonsense, since this process is no pure chance event, but biochemistry, adhering to biochemical laws. Larger and more complex molecules arising from smaller, simpler molecules in a continuous process of biochemical reactions and natural selection (yes, even at the molecular level). In fact, biochemists make use of this phenomenon by starting out with small molecules, letting them react in various ways, selecting the preferred more complex ones, continuing with those, etc. This way it is possible to create quite long and complex molecules surprisingly quickly, which could otherwise not have been made. It is called (simulated) molecular evolution.

  • Athena Andreadis October 1, 2010, 14:09

    Carl, I’m happy you liked my name suggestions. The idea was to stick with mythology, but go past the usual Roman-with-sprinkling-of-Greek-and Norse habit.

    Speaking of Goldilocks, we seem to have a meta-discussion along those lines between T1 (TK) and T2 (THair). Scientists shouldn’t be pedantic killjoys, scientists shouldn’t be exuberant ranters. They should react “just right” to communicate the sensawunda but still remain dignified and measured. In short, they can’t ever be human beings who dance with glee when they’ve just had an epiphany, or made a major discovery.

    As for life arising, one problem with mathematical models is that they treat all pre/biological processes as stochastic — from molecule assembly to protein folding. As a result, mathematicians and software developers keep droning on an on about the billiyuns of configurations of X and the unlikelihood therefore of Y… except they’re wrong.

    To give one example, proteins fold as they are synthesized, and in the cell’s very specific environment. This means they assume a local minimum energy configuration by optimizing hydrophobic/hydrophilic interactions and by forming individually weak but cumulatively strong hydrogen bonds, etc. There is a reason why human eyes are better at protein folding than the Rosetta algorithm. The latter is brute-force statistical thermodyamics applied to an entire protein chain. Which makes it an angels-on-pins exercise, and useless for real biology.

  • ljk October 1, 2010, 18:00

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


  • Ron S October 1, 2010, 18:49

    Martin: “There could be millions of whalesized creatures floating in space in our own solar system and unless they fell down on inhabited parts of the earth we would no be able to find them.”

    No, no, no. Not whales. Those are dinosaurs up there. That’s where they all went 65M years ago. They now know better than to come anywhere near us.

  • Bounty October 1, 2010, 19:26

    ….. and here I thought Gliese 581 G sounded cool. I don’t think we should give planets “real” names until someone lives nearby.

  • ljk October 1, 2010, 23:04

    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:


  • Athena Andreadis October 1, 2010, 23:28

    Although Vogt’s gesture is romantic, it also reminds me of Titan A. E. where the protagonists jokingly call their new home planet Bob. Also, I think it’s bad precedent to name planets after significant others. Like tattoos, this could become a problem should the relationship falter. Besides, the native inhabitants would object, with very good reason.

  • Paul Gilster October 2, 2010, 8:38

    I agree with Athena. A similar naming problem occurs in Michael Byers’ wonderful novel Percival’s Planet, in which one of the characters names a comet after a girl he’s chasing, who subsequently jilts him and leaves him the butt of endless jokes from fellow astronomers. Percival’s Planet is based on Tombaugh’s discovery of Pluto and is absolutely riveting, by the way. I’ll have a review of it up here in a few days.

  • TK October 2, 2010, 9:47

    I think it’s a nice name, I think Vogt did well choosing it, no need for names with some signification : the ones that get it won’t use it (scientists will keep using GI 581g) and the public will not care about what the name means.

    IMO what matters is that the names sounds good to the public (and of course the one who chose it but it’s a given). I just think that planets names ought to be feminines.

    I don’t think the native inhabitants would object more than with any other name, we can’t guess how they call it.

    No spectrometry :

    “We can’t resolve that question using conventional technology just from the light of its star. The planet doesn’t transit the star, so we don’t have a chance to see it. ”

    Thanks for the interesting link ljk.

  • bigdan201 October 2, 2010, 12:53

    In the book Rendezvous with Rama by Arthur C Clarke, astronomers used names from Hindu mythology (hence the name Rama). That book is great by the way, its a classic of hard scifi. Generally, I think the trend of using mythology is a good one, and we don’t have to limit ourselves to Greco-Roman.

    As per my previous comment, apparently wiki made a mistake and there are no cross-orbits… they have a new diagram up now.

    Personally, I’m looking forward to more information about this planet. The current gravity estimate is 1.1 – 1.7g, which is promising. I can only wait eagerly for more confirmed data.

    I’m sure others experienced this too, but this new discovery has sent my imagination in wild directions. Already, I’ve pondered this planet, and what it would be like to settle along the terminator, perhaps in permanent mild weather. What would happen on the sunlit side, how burning hot would that desert be? And how would the frozen night side take form? Would the great differences in temperature cause wild weather patterns, or would the atmosphere be stable?

    I agree with a recent entry on the wiki, which states that this planet has brought in a new age of discovery in exoplanetology.

  • Athena Andreadis October 2, 2010, 13:40

    TK — you are wrong about the significance of names. Naming is very powerful, it’s the first function of language. Uluru has a very different significance and connotation than Ayers, and Denali than Mt. McKinley. Also, if Vogt’s wife’s nickname were Betty or Daisy, I guarantee you the general interest in Gliese 581g would sink into a mire of snarks and snerks. Last but not least, there is no reason why planets should be “feminines” (sic), although we could use more female names in the planetary roundup. Too late for our own solar system but perhaps not too late for the rest of the universe.

    Larry, the io9 post you linked to used the modified diagram from my blog article, Once Again with Feeling: The Planets of Gliese 581. I started with Franck Selsis’ habitable zone picture, to which I added planet 581g (Ginny Keller originally created that for 581c, when the scientific community thought it might be Earth-like; the news was so recent that nobody had a depiction of 581g).

  • Athena Andreadis October 2, 2010, 13:48

    Postscript to my previous message: I think we can actually use more stars named after female figures, rather than the eternally trailing planets. Right now, all named stars that I can think of have male names. Which brings us back to the power of language to denote such things as importance and status.

    As for Vogt’s speculations about life, he’s as right or wrong as anyone else, given the total lack of information in that domain. However, the logic tat equates the likelihood of the origin of life to flipping coins is incorrect. As I discussed earlier in a different context, life processes are not stochastic, and there are conditions that do favor their development.

  • NS October 2, 2010, 15:09

    Ronald, could you elaborate on this?

    “Complex, even self-replicating molecules of several hundred C atoms length do indeed originate spontaneously and all the time.”

  • TK October 2, 2010, 15:53

    Athena :

    “Uluru has a very different significance and connotation than Ayers, and Denali than Mt. McKinley”

    You’ve kinda proved my point with this, I don’t know the significance of those names and I’m pretty sure most people don’t know it too, so significance or not it doesn’t change a thing for most people. Scientists don’t care either because they keep using the most practical names, eg “GI 581 g”. So in the end I don’t really see the point of having to chose a name with an appropriate significance … but of course I’m not against it.

    “Also, if Vogt’s wife’s nickname were Betty or Daisy, I guarantee you the general interest in Gliese 581g would sink into a mire of snarks and snerks”

    I’m sure that someone living in a country where Zarmina is a common name would have an opposite point of view. Assuming exoplanets names ought to be exotics for anglo-saxons, then yes Betty or Daisy doesn’t fit the bill … but that’s quite an assumption.

    “there is no reason why planets should be “feminines” ”

    Why do I see planets feminines ? Probably because in my language it’s a feminine name, but also I think there is some sort of sexual metaphor involved : the planets are receiving rays from the sun, you see what I mean ? That’s why I see planets feminines and stars masculines.
    Also I think that the way a mother is carrying a child is somewhat similar to the way “Mother Earth” is “carrying” us.

  • bigdan201 October 2, 2010, 17:21

    Yes, there is much in a name. The fact that we’re debating and considering a possible name for this significant world, instead of being content with “gliese 581 g” proves that.

  • Dave Moore October 2, 2010, 19:01

    Some thoughts:
    Ecentricities are a little suspect. They are often revised down after further observation. However, while e,b,c,and g are all probably tidally locked, tidally speaking d is in a similar position to Mercury and could well have a 3:2 resonance orbit, which would give it an eccentricity of 0.2. (If the 0.38 figure was right, this would put the planet in a 2:1 resonance situation.) f would presumably freely rotate.

    There is room for one and quite possibly two planets between d and f. If two were the case, this would give the system as many planets as our system. all inside the orbit of Earth. This system could easily have a dozen planets (a view of the system from g’s terminator would be spectacular). I wonder when the first system with more planets than ours will be discovered?

    As to the surface climate: Andy points out that this planet orbits outside a hot Neptune so it has probably migrated in from the outer system and is therefore likely to be completely covered with ocean.

    Merlis and Schneider ‘s paper: Atmospheric dynamics of Earth-like tidally locked aquaplanets covers it’s likely climate quite well. The atmosphere superotates making the climate quite mild. The coldest parts of the planet will be the poles and not the antistellar point. The ocean’s currents will transport a lot of heat to the planet’s dark side so parts of the ocean on the planet’s dark side won’t even be ice-covered. Steady Easterlies converging at the equator will keep the starward side temperate. Even at the sub-stellar point , the temperature will only be in the 30 to 35 deg. C range. The only problem is that all your tropical convergence occurs at one point, rather than a broad belt as on Earth, so the sub-stellar point gets approximately 600 inches (14,700 mm) of precipitation per (Earth) year.

  • Athena Andreadis October 2, 2010, 21:09

    TK, as dan201 said, the discussion over a suitable name for the putative Gliese planet proves my point. Also, recall that name changes are among the first things that happen during changes of regimes and a huge issue for prospective parents. If you haven’t noticed by now, my name (and natal culture) are not Anglosaxon — and I, for one, know the meaning and connotation of just about every celestial object. Other people clearly neither know nor care — but if so, I submit they shouldn’t be in naming committees.

    As for your sentence “there is some sort of sexual metaphor involved : the planets are receiving rays from the sun, you see what I mean?” I suggest you take a really long, hard look at your assumptions — and your knuckles; they’re scraping the ground right now.

  • Eniac October 2, 2010, 22:06


    life processes are not stochastic, and there are conditions that do favor their development

    I think most would have issue with the assertion that life processes are not stochastic, but even if it had merit, the processes that created life were not life processes, obviously, because they took place before there was life.

    Furthermore, we know nothing about those conditions that favor life, and it is quite conceivable that, whatever they may be, they were so special as to be highly unlikely themselves, even on the most “Earthlike” of planets.

    The universe is tuned to create at least one instance of life, that we know from observation. But there is no obligation to produce more than one, among all of the billions of billions of planets within it. In fact, assuming that tuning the universe to make life possible is already a stretch, the most parsimonious assumption would be that there is indeed just one. No need to go the extra mile from possible to likely, much less “100%”.

  • Joy October 3, 2010, 1:26

    Regarding getting an infrared spectrum of Gliese 581g. That is a tall order. The angular separation between the planet and the star is only 24 milli arcseconds. This is twice as close together as Hubble’s visible light resolution. In other words, even if Gliese 581 was a binary star, with the second, equally bright, star at the distance of 581g, Hubble would see it as a single star.

    The problem is compounded by the fact that stars are typically a million times brighter than their terrestrial planets. A vector vortex coronagraph made out of liquid crystal polymers has been installed on the Palomar telescope, and shows great promise in aiding detection of dim objects close to bright ones, so this problem may have a clever technical remedy.

    Still, the wavelengths of interest for a spectrographic search for life signatures are in the near infrared, requiring another fourfold increase in mirror size to obtain the same angular resolution as a visible instrument.

    The final answer is that you would need an infrared telescope with a mirror at least 20 metres in diameter, PLUS a next generation coronagraph to have any hope of getting a spectrum of Gliese 581g. The only good news is that next generation adaptive optics might allow ground telescopes to do the job.

    The the planned Thirty Meter Telescope, Giant Magellan Telescope, and Extremely Large Telescope – all hoping to be funded and built by the end of this decade – could possibly grab a spectrum from Gliese 581g.