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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.

  • Adam October 3, 2010, 1:37

    What would the angular diameter of the other planets be? They’re all so large the sky must be full of actual planetary disks since they crowd so close to that tiny little star! Some people actually see Venus as a disk/crescent due to unusually acute vision, but just about anyone could see planets in the sky there.

  • Eniac October 3, 2010, 13:02

    Wikipedia says (http://en.wikipedia.org/wiki/Optical_telescope):

    Recently, it has become practical to perform aperture synthesis with arrays of optical telescopes. Very high resolution images can be obtained with groups of widely-spaced smaller telescopes, linked together by carefully controlled optical paths, but these interferometers can only be used for imaging bright objects such as stars or measuring the bright cores of active galaxies. Example images of starspots on Betelgeuse can be seen here.

    Anyone know if telescope arrays are suitable for resolving planets from stars? That would seem like the best way to get spectra, and perhaps even images.

  • TK October 3, 2010, 14:32

    Athena, your analogy with the naming of other things is obviously irrelevant.

    About the gender of names I am pretty serious and I am reading your last sentence with a smile : are you denying the importance of the sexual analogy in the way we chose the gender of a name ? It’s not by chance that name’s genders are “feminine” and “masculine” in many languages … Of course since those are old words in almost every language the gender of planet and star were chosen without sufficient information at the time, different cultures had then different views of what eg the sun was, hence different genders.

    Since scientists don’t need fancy names because they are unpractical and since the public mostly ignores the meaning of the fancy names proposed by naming committees it seems to me that if someone choses a name without meaning they’ll be the only few to care.

    You are right saying that a name should sound good enough to interest people but since a name that sounds good to me probably won’t for a Chinese I think there’s a problem with naming planets, maybe each country should have its own naming committee but then we’ll have to use the scientific name to discuss in an international setting anyway. With billion stars and planets to name I don’t see much future for naming committees in astronomy.

  • Athena Andreadis October 3, 2010, 15:17

    TK, I don’t have the stamina to go through introductory linguistics and social politics with you. Assigned genders are arbitrary in all languages. Sun is female in German (die Sonne) and several other languages. Individual names have been known to shift as well (Evelyn and Shirley were once male names in English). And if you don’t understand something (or choose not to), it does not make it irrevelevant.

  • Joy October 3, 2010, 16:19

    @Adam – Yes, a human observer stationed at Gliese 581g would be able to see the other planets as discs with the unaided eye – assuming that the atmosphere is transparent.

    @Eniac – Although interferometer arrays have been the standard for radio astronomy for quite some time, optical/infrared interferometry is much more difficult. The Keck twins were supposed to operate routinely as an interferometer, 20 years on, it still isn’t really happening. Likewise the VLT.

    The CHARA array http://en.wikipedia.org/wiki/CHARA_array at Mt. Wilson has done some heroic high angular resolution work on very bright objects like the star Altair. Unfortunately, the light gathering power of the system is far too low to image dim objects like Gliese 581g. You really do need a big “light bucket” or an array of big mirrors to catch enough photons.

    NASA used to have plans for an optical/infrared interferometer in space, the terrestrial planet finder, but the plans have been shelved due to funding priorities. Of note, Gliese 581g was detected by a ground based telescope. With NASA underfunded and in chaos, our hopes for the next generation must lie with more ground based astronomy. We will need to wait until circa 2018 for the giant scopes to see first light.

  • Duncan Ivry October 3, 2010, 16:30

    A more funny and less pathetic name for the planet Gliese 581g would be “Stephen” (from Stephen Vogt). Yeah, “Planet Stephen” sounds nice.

  • Dave Bowman October 3, 2010, 16:38

    I noticed that the estimates of the age of the star Gliese 581 are 7 – 11 Billion years. Plenty of time for life to emerge if conditions are truly habitable. My concern is that perhaps the atmosphere of Gliese 581g is too dense with greater than Venus like pressures.
    Without the impact of the Mars size planet that created the moon, the atmospheric pressure on Earth may have been much higher. We have life on the bottom of our oceans with tremendous pressures, but those lifeforms migrated and adapted to live there? We live in interesting times.

  • andy October 3, 2010, 17:48

    One point to note about the Gliese 581 system is that there are three planets all located close to the habitable zone. The red dwarf Gliese 876 also has two planets close to its habitable zone. This goes to show that various claims that red dwarfs are unlikely to host planets in their habitable zones because of the small absolute widths of the HZ are not particularly plausible. Planets close to the star are packed closer together, and so the logarithmic scale of the habitable zone seems to be a more relevant consideration.

  • Joy October 3, 2010, 18:12


    PS: The planets closest to Gliese 581g (planets c and d) would have an angular diameter around 6 arc minutes at their closest approaches. This is intermediate between the largest angular diameter of Venus (1 arc minute) and the moon (about 30 arc minutes).

  • Nathan Currier October 3, 2010, 22:05

    The view from the night side of Gliese 581e would be even better. If b is the size of Neptune, it would appear to be 3x wider than our moon at closest approach to e. It recieves 8x the light flux as our moon, and if it has sulphurous clouds it might have an albedo 6.6x higher than our moon. Under these conditions, the bolometric luminosity of b as seen from e would be 3^2*8*6.6 = 475 full moons. Steady illumination at this level could maintain a methane atmosphere, and there are far more extreme cases of planetshine than this setup… but atmospheric stripping on the dayside would still destroy any hope of habitability.

  • Eniac October 3, 2010, 22:38

    @Joy: Thanks for the excellent clarification on optical arrays. It seems to me that this is a field that may advance greatly in the near future, likely to provide us with a few more breakthroughs in ground based extrasolar imaging during the next decade. Along with those “vector vortex coronagraphs” mentioned earlier.

    See here (http://www.mrao.cam.ac.uk/telescopes/coast/betel.html) for a star surface image, and here (http://en.wikipedia.org/wiki/Coronagraph#Extrasolar_planets) for an imaged planetary system.

    These are truly exciting times.

  • bigdan201 October 4, 2010, 7:48

    TK, what are you talking about? Names are of significance in many different situations. Consider the change from St. Petersburg to Leningrad and back, or Constantinople to Istanbul, and so on. My last name tells me that some of my ancestors came from western Germany, specifically Alsace-Lorraine under the 2nd reich.

    With the exception of Venus, astronomy does rely on masculine names. We could certainly use more variety for new discoveries.

    Although many objects in astronomy will have technical names, anything that is especially relevant or significant to us will get a non-technical name. What that will be remains to be seen – but I believe that the more hospitable Gliese 581 g is, the more difficulty we will have in christening it.

    Anyway, this discovery will have a number of great effects. Increased interest in space, an impetus for eventual interstellar colonization, and it will encourage development of systems/technology to help us locate and describe exoplanets. The third is of particular relevance – now that we’ve made this find, it will be easier to fund exoplanet research, which may lead to more info on this place and knowledge of more planets.

  • Eniac October 4, 2010, 9:13


    … but atmospheric stripping on the dayside would still destroy any hope of habitability.

    This is discouraging. Do you have it on good authority?

    Contrast with previously posted here by Dave Moore:

    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.

  • andy October 4, 2010, 15:15

    Eniac, I think Nathan is talking about the inner planet “e”, rather than “g”.

    Nevertheless, there is a question of whether super-Earths can sustain geomagnetic fields. The high pressure conditions in the core make sustaining a dynamo look like a tricky propositon.

  • Joy October 4, 2010, 16:54

    Of note, I was in my backyard binocular observing one of the stars in the website logo last night, Gamma Crucis, and looked up the data on it. I was later amused when I found it to be the same colour as Gliese 581. The B-V index of the bright red star at the top of the Southern Cross is 1.60, almost identical to the B-V index of Gliese 581 which is 1.61.

  • Nathan Currier October 4, 2010, 20:30

    @Eniac, Andy

    I was thinking about e and possibly more extreme planets… until I realized there weren’t any, not even in the 55 Cancri system, which has a hot Jupiter plus a small inner planet. Gliese 581b –> e is currently the most extreme case of planetshine known, although I am pretty sure there are hot Jupiter / cthonian planet pairs in 2:1 orbits. If Wasb 33b had such a planet inside its orbit (unlikely), a rough calculation indicates that Wasp 33b could give its nightside up to ~30x more illumination than Earth recieves during the DAY. (Wasp 33b would be about 17x wider than the full moon!)

    Such a setup would be interesting because the cthonian planet would have plenty of organics during its last gasp as a gas giant. I was wondering if the nightside of a cthonian planet could be habitable due to planetshine alone. It would probably all come down to whether there could be a high and stable “moat” to prevent the atmosphere from migrating to the day side. The moat would be just behind the terminator and would hopefully first form by mineral rain, because tidal heating would undermine an ice moat. If this works you could have a nightside oasis with spectacular views, surrounded by a range of very high mountains. The other side of the planet would be molten.

  • TK October 4, 2010, 20:33

    Bigdan201 maybe I wasn’t clear enough, but I am talking about names ONLY in astronomy, of course I completely agree with you that it’s a very different matter when we are naming a ministry or a changing the name of a town, by the way notice that in all those cases those changes are directly headed to the population, they are understandable, they have a strong political meaning for everyone. In NO way we can compare this to the naming of exoplanets whose names are not understandable by the population and are useless to scientists.

    I agree that a name is important to catch the public’s attention (I stated this before too) but as the publics doesn’t understand the meaning of a fancy name it wouldn’t change a thing if the name had a meaning or not (unless it’s easily understandable of course).

    I think we agree that since scientists don’t use those kinds of names they have to be aimed to the public so it hopefully brings more people toward science. In this regard international naming is pointless because it won’t achieve that goal (for a Chinese Duncan Ivry’s proposition is probably as good as Zarmina or … Yemanja.) therefore it has to be done at a nation’s scale.

    Athena your statement “genders are arbitrary” has been proven wrong, the truth is “genders are MOSTLY arbitrary” besides do you even know what linguists mean with “arbitrary” ? It just means that it wasn’t the choice of some intelligentsia but the fruit of a global social process. But every social process involves people obviously and as far as it was possible they unconsciously attributed genders according to their perception of things (be it related to mythology, the shape of an object, its use or whatever: words such as “hammer” or “power” are almost always perceived as masculine for obvious reasons and it just came to my mind that on forums related to guitar even English speakers refer to a guitar as a “she”, I don’t know why, it might be related to the shape of the object). In French we have the word “sexuisemblance” it would be useful if it existed in English … we could say that a word like hammer is “sexuisemblant” because it’s masculine and seen as masculine by almost every culture (I lost the link about “hammer”, but you can find this easily if you really are interested).

    In most languages the genders of the Sun and the Moon were based on personification (different genders in no way it proves that genders are arbitrary only that different cultures had different views on the Sun and the Moon) and I think that if all populations had at the time the same information (eg what the Moon and the Sun actually are) the genders they’ve assigned to them would have been much more homogenous.

    There are a lot of studies stating that grammatical gender carries meaning, do some research and read some papers, you don’t have to believe me.
    You could find much much more using Google for 2 minutes.

    Also there are still new names created and Michel Roché stated that the attribution of the grammatical gender for those is not random, not arbitrary but the result of many factors : morphological, phonological, syntactical, semantic (that’s specially what I was talking about previously), lexical, etc.
    If you can read French it’s here http://www.persee.fr/web/revues/home/prescript/article/lfr_0023-8368_1992_num_96_1_5785

    I’m just writing why I think planets names ought to be feminine and stars names masculine, a bit like Gaston Bachelard when he was asking himself why water was perceived as feminine and fire as masculine by French people, and yet you seem to find this almost offensive …

    About social politics, do you really consider that naming an exoplanet is comparable to the naming of a ministry ? I’m sorry but if you really think that you have no clue about social politics … The same goes for naming a child and sociology. The name of a child, of ministry and of an exoplanet don’t share the same functions, need I say more ?

    My English is probably painful to read, sorry about that.

  • TK October 4, 2010, 21:33

    I know that my last message is already way to long but I’ll just say that in some languages like Berber the feminine gender is also used to denote that something is smaller, in that regard we could consider that planets are feminine because they are smaller than stars… please don’t get mad at me :p

  • Nathan Currier October 4, 2010, 23:27

    Re: my previous comment:

    While I had visions of an Iapetus-like ridge near the terminator, “Levy” or “bathtub” is a better description of the ring of condensed minerals which might contain an atmosphere on the night side of a cthonian planet. Strangely enough, the atmosphere might actually be oxygen stripped from silicates on the blazing dayside. (see http://en.wikipedia.org/wiki/COROT-7b).

  • Ron S October 5, 2010, 14:37

    Nathan: “Strangely enough, the atmosphere might actually be oxygen stripped from silicates on the blazing dayside. ”

    Ouch! I had hoped there would be a low probability of an oxygen atmosphere for any cause other than life. This could make it more difficult to unambiguously determine the presence of an active biosphere, especially on planets around red dwarfs.

  • andy October 5, 2010, 16:21

    Ron S: another plausible way to get atmospheric oxygen is via photodissociation of water vapour on ocean planets (i.e. worlds like Ganymede that have migrated into the habitable zone). With a mantle of high-pressure ice thousands of kilometres thick separating the ocean from the rocky core, when the hydrogen escaped from the planet the oxygen would tend to hang around.

  • Ronald October 5, 2010, 18:49

    Nathan, andy: interesting and very relevant points with regard to future biosignature detection, O2 from silicates and from water photodissociation.

    However, since O2 is quite reactive I would expect the atmospheric O2 levels to be (much?) lower in those cases than our earthly level where it is constantly replenished at very high rate by photosynthesis.

    What do you think?

  • Eniac October 6, 2010, 0:37

    Good point about the rock pyrolysis. It generates SiO and O, the former could precipitate at the terminator to build the “wall”, and the latter could form an O2 atmosphere on the night side. On the hot side, there would be lakes of silicon left behind. And other metals, probably, too. A metallurgists dream.

    No carbon allowed, though, or the oxygen would be gone, quickly.

  • joseph October 6, 2010, 1:27

    I would ask what evidence that the tremendous amount of o2 stored in our atmosphere is all derived from photosynthesis? Where did all the carbon go? while the deposits of coal and oil may indicate SOME of the o2 came form the reduction of CO2 to O2, with subsequent burial of the plant materials , I do not think it is enough to account for all the oxygen. another idea is that earth’s primitive atmosphere had lots of ammonia and water vapor, and at high altitude UV light split the molecules and some fraction of the Hydrogen atoms escaped, while the heavier Nitrogen and Oxygen stated behind. Thus we have a nitrogen and Oxygen atmosphere ! very “oxidizing” ! Photosynthesis, which may have been around for a while , began to dominate the biochemistry of the planet as organisms that hat a source of reduced organic compounds began to rule. before that, Organic compounds were not limiting, only the energy to convert them from one form to another. Now this new planet has two differences, less UV light to release Hydrogen, and a much deeper gravity well making it harder to escape. a deeper atmosphere is possible and likely, so no real problem with freezing out on the “dark side”. it may actually be a ” Baby Gas Giant ” with only a smallish ( earth sized?) rocky core. Or maybe it is a “super venus” ( which has a LOT more atmophere than earth) .

  • Eniac October 7, 2010, 0:59


    There isn’t really “a tremendous amount” of oxygen in the atmosphere. Its residence time is only 4,500 years, and the flux is almost completely biogenic. Check out the details here: http://en.wikipedia.org/wiki/Oxygen_cycle

    As I have heard it, it took photosynthesis a couple of billion years to fill the lithospheric reservoir before the spillover could accumulate in the atmosphere, where it is held in check by respiration. And, I believe, wildfires, but I could not find evidence for that.

  • david lewis October 7, 2010, 8:59

    An interesting comparison between Gliese an our own system would be that we both have 3 planets that are in or close to the goldilocks zone.

    Here we have:
    Venus – thought to have had oceans before a runaway greenhouse effect took over
    Mars – which we know had oceans in the past
    Earth – which still has oceans

    With Gliese we have talked of the possibility of liquid water on three of its worlds.

    If this sort of distribution of planets within a system is common then it might be the case that plants with the potential for life are very common, maybe even out numbering the number of stars in our galaxy. Maybe our own system with just 1 life bearing world was in fact unlucky and it might be more common for such systems to have 2-3 life bearing worlds.

  • andy October 7, 2010, 9:48

    @david lewis: probably if Mars were a more massive planet it could have been habitable up until the present day. Furthermore, planet formation models have real trouble with generating Mars-analogues that are as small as the actual planet: generally the planets they form at that location tend to be on the same scale as the Earth and Venus, which bperhaps suggests that we may indeed have got unlucky with only one habitable terrestrial planet. Hopefully space-based microlensing missions might give some clue as to the terrestrial planet distribution near the habitable zone.

  • little_xav October 7, 2010, 15:35

    the ruler analogy is flawed – won’t the calipers also compress under the force of gravity?

  • Eniac October 7, 2010, 18:03

    the ruler analogy is flawed – won’t the calipers also compress under the force of gravity?

    Not if you hold them with the handle up. In such a case, the calipers would be elongated by gravity and you would measure an exaggerated effect.

  • andy October 11, 2010, 3:47

    Presentation by F. Pepe at IAU Symposium 276: it turns out that Gliese 581 g is not present in new data from HARPS.

  • Dwight Williams October 11, 2010, 11:06

    Is it politically possible for NASA to now dust off those Terrestrial Planet Finder plans in the wake of the Gliese 581g news breaking?

  • ljk October 12, 2010, 0:29

    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:


  • ljk October 14, 2010, 1:56

    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:


  • Athena Andreadis October 14, 2010, 12:17

    TK, it’s not your English that’s painful; it’s the “facts” of your posts, as well as the mindset they convey. As I said before on this thread, I don’t have the time and stamina to educate you, even if I thought it might be productive: Is It Something in the Water? Me Tarzan, You Ape

  • ljk May 9, 2011, 9:52

    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:


  • ljk October 27, 2011, 13:06

    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:


    An astronomer picked up a mysterious pulse of light coming from the direction of the newly discovered Earth-like planet almost two years ago, it has emerged.

    Dr Ragbir Bhathal, a scientist at the University of Western Sydney, picked up the odd signal in December 2008, long before it was announced that the star Gliese 581 has habitable planets in orbit around it.

    A member of the Australian chapter of SETI, the organisation that looks for communication from distant planets, Dr Bhathal had been sweeping the skies when he discovered a ‘suspicious’ signal from an area of the galaxy that holds the newly-discovered Gliese 581g.

    The remarkable coincidence adds another layer of mystery to the announcement last night that scientists had discovered another planet in the system: Gliese 581g – the most Earth-like planet ever found.

    Dr Bhathal’s discovery had come just months before astronomers announced that they had found a similar, slightly less habitable planet around the same star 20 light years away. This planet was called Gliese 581e.