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‘Super-Earth’ in a Triple Star System

GJ 667C is an M-class dwarf, part of a triple star system some 22 light years from Earth. Hearing rumors that a ‘super-Earth’ — and one in the habitable zone to boot — has been detected around a nearby triple star system might cause the pulse to quicken, but this is not Alpha Centauri, about which we continue to await news from the three teams studying the prospect of planets there. Nonetheless, GJ 667C is fascinating in its own right, the M-dwarf being accompanied by a pair of orange K-class stars much lower in metal content than the Sun. The super-Earth that orbits the M-dwarf raises questions about theories of planet formation.

Thus Steven Vogt (UC Santa Cruz), who puts the find into context, noting that heavy elements like iron, carbon and silicon are considered the building blocks of terrestrial planets:

“This was expected to be a rather unlikely star to host planets. Yet there they are, around a very nearby, metal-poor example of the most common type of star in our galaxy. The detection of this planet, this nearby and this soon, implies that our galaxy must be teeming with billions of potentially habitable rocky planets.”

Image: An artist’s impression of a super-Earth planet. Credit: ESO/M. Kornmesser.

Nearby is right, and assuming we do eventually develop the technologies to send probes to distances of tens of light years out, this super-Earth would surely gain a place high on the target list. The reference to the most common stars in the galaxy is drawn from estimates that 75 to 80 percent of all stars in the Milky Way may be M-dwarfs, although the relative percentages will surely be adjusted as we get a better handle on the distribution of brown dwarfs. Vogt refers to multiple planets because in addition to the super-Earth orbiting GJ 667C, there appears to be evidence for additional planets, perhaps as many as three, orbiting the same star.

Building on earlier work on a different super-Earth in the same system (GJ 667Cb), too close to the star to allow liquid water to exist on its surface, the research team found the signature of the new planet GJ 667Cc, with an orbital period of 28.15 days and a minimum mass of 4.5 times that of Earth. Guillem Anglada-Escudé (Carnegie Institution for Science) calls the latter world “…the new best candidate to support liquid water and, perhaps, life as we know it,” though we have to add the usual caveats about flare activity on M-dwarfs and their potential for disrupting life.

Those other worlds in the same system? A possible gas giant and yet another super-Earth are candidates, but neither has been confirmed. Meanwhile, GJ 667Cc is thought to absorb about the same amount of energy from its star that the Earth draws in from the Sun, leading to the possibility of Earth-like temperatures and, if conditions are right, the potential for liquid water. As with all such results, further information about the planet and its atmosphere are needed before we can run too wild with such speculation, but GJ 667Cc clearly deserves a much closer look.

The paper is Anglada-Escudé et al., “A planetary system around the nearby M dwarf GJ 667C with at least one super-Earth in its habitable zone,” accepted at the Astrophysical Journal Letters (preprint).

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Comments on this entry are closed.

  • Tulse February 2, 2012, 11:51

    This is a great find — such a short orbital period and close proximity provides excellent opportunity for getting atmosphere spectra and other important info.

  • Abelard Lindsey February 2, 2012, 12:56

    This, along with other recent discoveries, should make clear that current theories of planet formation are incomplete or wrong.

  • James D. Stilwell February 2, 2012, 13:52

    WOULD HAVE RAISED MANY EYEBROWS HAD THE GJ 677Cc NEW EARTH BEEN ACCOMPANIED BY A SATELLITE OF SAY ONE QUARTER SIZE THE PARENT PLANET. OH, WELL. SUCH IS LIFE. I WILL BE PATIENT AND AWAIT THE MIRACLE TO COME. IT WILL COME.
    JAMES D STILWELL

  • Alexander McLin February 2, 2012, 14:09

    Was there enough information to determine if GJ 667Cc is a tidally-locked planet?

  • Zen Blade February 2, 2012, 14:47

    This is huge, if this find is confirmed. And the planet’s orbit is something like just under a month, if I remember correctly.
    Very exciting, and it’s so close.

  • henk February 2, 2012, 15:12

    Zen Blade

    it is confirmed

  • Tony P February 2, 2012, 15:55

    Such a low orbital period suggests that the planet is indeed tidally locked. A pity if true. 22 LY is a hop skip and a jump away in interstellar terms.

  • Ronald February 2, 2012, 16:13

    Great discovery, but: such a planet is almost certainly tidally locked, implying that “the same amount of energy from its star that the Earth draws in from the Sun” would probably not be leading to Earth-like temperatures.

  • FrankH February 2, 2012, 16:20

    This world is slightly more Earth-like that the Neptunian Kepler 22b. At the minimum mass of 2.7 x 10^25kg (4.5x Earth) and assuming that the same density, we’re looking at a world with a 10,500km radius and a surface gravity of at least 1.6x Earth’s. Slightly lower density means bigger radius and slightly lower surface gravity but we’re still looking at an uncomfortably large planet with a potentially thick atmosphere just capable of holding on to hydrogen. Throw in a red dwarf primary and it’s not looking as rosy as the PR makes it out to be.

  • Raffaele Antonio Tavani February 2, 2012, 16:22

    Interessante articolo…
    http://astrobio.net/exclusive/4531/elements-of-exoplanets

    Un saluto a tutti i lettori di questo “blog” scientifico, da parte di Antonio.

  • Ronald February 2, 2012, 16:25

    The metallicity of this star, according to what I could find, is only about 25-30% of solar.
    It is truly amazing that such a metal-poor star can harbor such a wealth of planets.
    Ok, it was already known from HARPS and Kepler data that high metallicity is of particular importance for gas giants, but Kepler data also suggested that below a certain lower metallicity threshold (about 1/3 of solar, if I am not mistaken) any planets would be rare.

    If this appears to be a common thing, planet formation models may have to be revised.

  • ljk February 2, 2012, 16:43

    James, this superEarth could have a moon or two, they are just hard to detect at this point. Now whether any of this means the planet or even its hypothetical moons have life is another matter that will be even harder to determine for now.

  • JohnHunt February 2, 2012, 17:00

    With something this size so close, I figure that there’s got to be something good even closer. They say there are about 100 stars closer. We really need a pan-sky census where we could detect planets about half the size of Earth. And if not pan sky then looking at our nearest neighbors.

  • Alex Tolley February 2, 2012, 17:59

    If the planet is tidally locked, doesn’t that imply a potential temperate zone on some longitudes plus farside protection from solar flares? If the temperate zone reaches into the farside hemisphere, then it is also protected from flares and therefore a potential habitable zone on the surface.

  • drakend February 2, 2012, 18:26

    Let’s not forget about rogue planets. Can’t that planet just be a rogue one captured by the three stars’ gravity?

  • Dave Moore February 2, 2012, 18:57

    GJ 667Cc being tidally-locked doesn’t necessarily make it uninhabitable.

    See these animations by Tapio Schnieder of Caltech, which shows what the climate of Earth would be like if it was tidally locked.
    http://www.gps.caltech.edu/~tapio/animations.html

    However, the weather patterns on the artist’s impression are almost certainly wrong.

  • andy February 2, 2012, 19:03

    Of the currently-published habitable planet candidates, this one interests me the most because it receives an insolation that is comparable to past insolation of the Earth (~90% of current insolation) depending on models of stellar evolution. Of course it is unfortunate that we only have a minimum mass and no information about the radius of the planet, will be interesting to know what kind of limits can be placed using dynamical arguments.

  • Rob Henry February 2, 2012, 19:08

    I don’t mind making huge assumptions, but I begin to worry when we pile them one atop the other and conclude that all higher life lives on Earth-like planets.

    FrankH pointed out GJ 667Cc’s high hydrogen retention potential and possible high surface gravity. I note the following.

    1) That its surface gravity might be up to 160% that of Earth’s. If so, we could still colonise it without genetic modification or mechanical enhancement necessary – although it would very uncomfortable for us without either assistance. It is very hard to imagine that this small difference would be any impediment at all to the development of native life there.

    2) Presumably that the likely high hydrogen retention makes the slow development of an oxygen atmosphere there unlikely. And that thought EITHER requires assumptions about rocky material coalescing in a metal poor protoplanetary disc at a similar rate to higher metallicity systems (and before the volatiles dissipate), OR that this setup would disallow an Earth-like sequestration of reduced material by photosynthetic life.

    3) We then next assume that that high H2 is somehow bad. Why can’t very high hydrogen levels also support higher life? Actually, assuming that most complex life is limited by diffusion limitation considerations (as it is for life on Earth), hydrogen is ten times more potent per atmospheric weight fraction as a gas supporting carbohydrate utilising metabolism. Carbohydrates reduction by H2 also release fully a third the energy of its O2 oxidation, and for Earth-life carbohydrate energy density has proved so little trouble that even humans store them with water of hydration that is TEN times their anhydrous weight.

    If his intention was to infer that this system is of little exobiological interest, I wish to register my objection. That just assumes too much.

  • Bob February 2, 2012, 20:25

    “WOULD HAVE RAISED MANY EYEBROWS HAD THE GJ 677Cc NEW EARTH BEEN ACCOMPANIED BY A SATELLITE OF SAY ONE QUARTER SIZE THE PARENT PLANET.”

    Are you suggesting that to be earth like it is a requirement to have a moon?

  • jkittle February 2, 2012, 22:11

    Low metallicity may imply lower density and thus a relatively large diameter, so the gravity will fall between 1 and 2 g possibly lower than 1.5 g
    The redder spectra of the star and the higher escape velocity implies that hydrogen is easier to retain – so no oxygen atmosphere ( the o2 in the earths atmosphere is mainly from H escape, not carbon sequestration by biological processes) .
    Life seems possible there, and even life like that on early earth. And only 20 ly away. If we reach ANYWHERE outside the solar system we should be able to reach this far. One concern the planet may be bigger than we hope, 4.5 x earth mass is a minimum . I do not know about being tidal locked but with the thicker and lower molecular weight atmosphere, it is likely that even a tidally locked planet might have circulation adequate to even out the temperature. It is also possible that its rotation is in resonance, so that it is some simple ration of the orbital period.

  • Phil February 2, 2012, 23:47

    The debate about the habitability of tidally locked M dwarf planets will doubtless go on and on. In the meantime, we are only a month into 2012 and its already turning out to be an amazing exoplanet year, what times we live in eh?

    If we get some news from the a Cen system this year it’ll be icing on the cake.

    Oh, and I suspect the headline-grabbing Vogt hasn’t entirely abandoned Gl581g yet either :)

    P

  • johnq February 2, 2012, 23:51

    I didn’t quite know where to bring this up but lately I have been reading a book by a physicist who argues in the course of it (it’s a bit of a long one so I will just mention this one item) that planets with axial tilts similar to Earth/Mars/Neptune should be common. Even garish examples like Uranus would not be unlikely. The question then arises, since we are all interesting in going to the next step in detecting physical characteristics of these worlds, how difficult is it to detect axial tilt across the light years? Would it just be a matter of detecting reflective/seasonal variations, assuming the planet has an atmosphere? But what if it doesn’t? What if the planet is close to its star? Or far away? Could it be a hard problem or one that has already been solved? Case by case, or is there a general method? Thoughts?

  • Joy February 3, 2012, 0:25

    Does anyone dispute that this globe could hold vastly more astro-biological promise than Enceladus or Europa?

  • Nick February 3, 2012, 1:33

    Alex Tolley: “…a potential temperate zone on some longitudes plus farside protection from solar flares? If the temperate zone reaches into the farside hemisphere, then it is also protected from flares and therefore a potential habitable zone on the surface.”

    This is a great observation, but a remaining problem is photosynthesis. The planet would need a very thick atmosphere that blocks almost all the ultraviolet but still lets in enough optical for photosynthesis. Given the size it probably does have a very thick atmosphere like Venus. But also like Venus it probably has an optically thick cloud cover.

    In any case, however habitable, the planet is with extremely high probability lifeless for reasons discussed in earlier threads.

  • FrankH February 3, 2012, 1:47

    @Rob Henry
    We’re looking at a potentially tidally locked, massive planet around a low metallicity red dwarf. It’s mass suggests a thick atmosphere. It’s location suggests a high surface temp and the potential for a runaway greenhouse effect. The low metallicity suggests a planet very different in composition to any of the terrestrial planets. It’s an interesting world for sure, but literally a dime a dozen… Which brings me to my biggest issue. I wish people would stop calling these planets “super-Earths”. The name implies a world like our own, with life or the almost certainty that they have life, Venus is more Earth-like than most of these LARGE TERRESTRIALS and no one is planing on haunting over for a tropical vacation any time soon.

    I also wouldn’t be surprised if this planet moves out of the HZ once the paper comes out. Unlike a G dwarf, where you can use the star’s V absolute magnitude to arrive at a good approximation of its luminosity, You have to use a red dwarf’s bolometric magnitude to calculate its luminosity. Unless it’s been measured directly, it’ll have to be estimated and may be way off.

  • amphiox February 3, 2012, 2:21

    Are you suggesting that to be earth like it is a requirement to have a moon?

    Possibly, but I think the other implication is that a moon a quarter of the size of a planet 4.5X the mass of the earth would basically be earth-sized.

  • Adam Crowl February 3, 2012, 5:46
  • Martin J Sallberg February 3, 2012, 7:18

    A dense atmosphere and/or strong winds can redistribute heat from the dayside to the nightside. Strong winds may help the evolution of intelligent life by forcing native life to evolve hands to cling with. Lifeforms may evolve early warning senses for detecting flares in time and take shelter.

  • Antonio February 3, 2012, 12:15

    Salve, a voi tutti.
    Vi segnalo un’altro, interessante articolo.
    http://www.media.inaf.it/2012/02/03/scienziati-in-campo-per-gli-esopianeti/
    Saluti da Antonio.

  • amphiox February 3, 2012, 12:23

    ( the o2 in the earths atmosphere is mainly from H escape, not carbon sequestration by biological processes)

    The O2 in earth’s atmosphere is from carbon sequestration from geological processes, not biologic ones, and H escape. You need both.

  • amphiox February 3, 2012, 12:25

    In any case, however habitable, the planet is with extremely high probability lifeless for reasons discussed in earlier threads.

    Given current knowledge and available information, I think declaring “extremely high” probability in either direction is rather premature.

  • Mike February 3, 2012, 12:50

    I wonder what planets may exist at GJ 667 AB.

  • Rob Henry February 3, 2012, 16:37

    The question of how much of an impediment to life tidal locking is interesting. I imagine that on flare stars, most higher plant life is sufficiently close to the terminator *rim* to pull back into the permanent shadows of hillsides at the first signs of flare activity. Perhaps this alien setup in an inducement the production of higher life rather than precluding it??

  • Nick February 3, 2012, 16:39

    “Given current knowledge and available information”

    We have petabytes of information about the cosmos, including on more than 100 billion galaxies at a variety of wavelengths, and in all that there is not a shred of evidence for a technological version of the Malthusian imperative at work anywhere in all this vast space besides our own planet. Life has invariably operated according to that imperative here on earth for more than 4 billion years. If a technological Malthusian imperative had been operating in any nearby galaxy for the hundreds of millions of years of average head start we’d expect, it would be blatantly obvious — nearly all the surfaces of the galaxy would look blatantly artificial — and we would have discovered it decades ago.

    This vast body of data confirms our observations of life itself, particularly the astronomical complexity/improbability of the simplest known closed ecosystem. Both pieces of evidence, both involving vast amounts of data, tell us that life is astronomically rare — probably far less than one independent origin per galaxy.

    Of course, astrobiologists, in order to make a living at their “science without a subject”, must argue otherwise.

  • andy February 3, 2012, 17:29

    a technological version of the Malthusian imperative

    What is this supposed to mean exactly? Any reason for this weird jargon or are you just trying to sound pretentious?

  • Nick February 3, 2012, 19:04

    “a technological version of the Malthusian imperative”

    The Malthusian imperative is what Malthus (and Darwin and Wallace whom he inspired) observed about life: that it will expand to fill all feasible niches. If life could expand to other worlds, it would (indeed Malthus said just this).

    Technology makes that possible for ETI civilizations older than ours (i.e. practically all of them). And where it’s possible, it will happen: until it has covered every available surface in a galaxy. That is the technological Malthusian imperative.

    And indeed, we only need the Malthusian imperative to be followed by even a very small fraction of ETI to still have enough artificially surfaced galaxies in our sky to be blatantly obvious to our astronomers.

  • amphiox February 3, 2012, 20:26

    We have petabytes of information about the cosmos, including on more than 100 billion galaxies at a variety of wavelengths, and in all that there is not a shred of evidence for a technological version of the Malthusian imperative at work anywhere in all this vast space besides our own planet.

    What has technology to do with an argument about LIFE, not technological intelligence?

    This vast body of data confirms our observations of life itself, particularly the astronomical complexity/improbability of the simplest known closed ecosystem. Both pieces of evidence, both involving vast amounts of data, tell us that life is astronomically rare — probably far less than one independent origin per galaxy.

    No, it does not. And never will. No amount of observation of any kind, to any degree of detail, no matter how vast, when limited to life on this one planet, says anything valid whatsoever about life on an astronomical scale.

    You cannot generalize about distribution, rarity, or probability from a denominator of one. No matter how vast your information about that one is. It is a probabilistic fallacy that both sides of the argument constantly make.

    “Life on earth appeared so quickly early in the planet’s history that life must be plentiful elsewhere”. NO.

    “Life on earth is so complex that it must be very rare.” NO.

    All such arguments are evidentially, logically, and probabilistically untenable. They are ALL wishful thinking and nothing. And they will remain so until at least one other independent example is discovered with which earth life can be compared to.

    At present, the only probabilistic argument we can make with current information are these:

    The probability that life will arise on a planet with conditions identical to that of earth after 4.5 billion years of time is precisely 1:1.

    The probability that life, having arisen on a planet with conditions identical to that of earth, evolving in a direction that produces a technologically competent intelligent species, after 4.5 billion years is precisely 1:1.

    The total number of extant habitable planets in this universe that currently do support life is some number equal to or greater than 1.

    And as for the so-called “astronomical complexity/improbability of the simplest known closed ecosystem”, astronomically complex COMPARED TO WHAT? Improbable WITH RESPECT TO WHAT? There is no metric for comparison, and the statement is utterly meaningless without one. The universe is astronomically vast. Is the astronomical vastness of the universe greater than the astronomical complexity of the “closed” ecosystem, or less? Great enough to easily accommodate the astronomical improbability, or not? One can easily apply rhetoric to either side, and the rhetoric will be equally empty for both.

    Without at least one other independent example to use for comparison, IT IS IMPOSSIBLE TO SAY ONE WAY OR ANOTHER, NO MATTER HOW VAST YOUR KNOWLEDGE ABOUT THE ONE EXAMPLE YOU DO HAVE. Whether you know just one thing about it or a googleplex of things about it MEANS ABSOLUTELY NOTHING with respect the questions of probability.

    Absolutely nothing.

  • amphiox February 3, 2012, 20:33

    I imagine that on flare stars, most higher plant life is sufficiently close to the terminator *rim* to pull back into the permanent shadows of hillsides at the first signs of flare activity.

    Considering the degree of radiation resistance some earthly organisms display, it is entirely possible that lifeforms on such a planet would simply evolve to be resistant to even the worst flares from the parent star. Or even evolve a life cycle dependent on the flare activity (where flare activity kills off one life stage, but actually induces the next life stage to germinate from protected spores/seeds/cysts, like how some plants on earth adapt to fire).

    As for the probability of such things? Well, see my prior posts for my opinion about opining about that….

  • amphiox February 3, 2012, 20:36

    The other thing to consider about flare activity. No matter how intense the flares are, if the planet has water, there will be some depth below which organisms will be protected from even the worst of the flares. If the planet has rocks and is not a perfectly smooth cueball, there will be some places with sufficient shade to protect from the flares.

  • Phil February 3, 2012, 21:58

    This paper isnt from the HARPS team that generated the RV set in the first place. I believe there is one in the pipeline. Lets see what they have to say – it might be quite different!

    P

  • Nick February 4, 2012, 2:52

    amphiox, probability theory certainly does not disprove the reasoning I have outlined. In particular see the Kolmogorov complexity literature on measuring the complexity and improbability of particular objects in an absolute way, rather than as a measure relative to other objects.

    amphiox: “if the planet has water, there will be some depth below which organisms will be protected from even the worst of the flares.”

    But it may be too deep or the water too murky for photosynthesis to occur at any safe depths. Worse, super-earths probably have very thick cloud covers that prevent photosynthesis in the first place (and/or create an intense greenhouse effect as on Venus). Also, if free oxygen can’t accumulate due to an abundance of hydrogen, no ozone layer will form, resulting in an even greater relative flux of ultraviolet radiation. Assuming for the sake of argument life somehow appears there in the first place, it might often be prevented from evolving productive photosynthesis.

  • andy February 4, 2012, 6:03

    I wonder what planets may exist at GJ 667 AB.

    The GJ 667 AB system has quite an eccentric orbit, and the periastron is about 5 AU. This does not look like a good setup for planet formation. I wouldn’t expect there would be much in the way of planets around either. Of course the exoplanets field has produced quite a lot of surprises so far.

    As to that potential gas giant inferred around GJ 667 C, that would be really perplexing if confirmed: both the low metallicity and low mass of the host star are factors that should disfavour gas giant formation. Perhaps gravitational instability rather than core accretion was at work?

    This is a great observation, but a remaining problem is photosynthesis. The planet would need a very thick atmosphere that blocks almost all the ultraviolet but still lets in enough optical for photosynthesis. Given the size it probably does have a very thick atmosphere like Venus. But also like Venus it probably has an optically thick cloud cover.

    Is ability to support photosynthesis really relevant to whether a planet has life or not? Last I heard the idea that life may have formed at hydrothermal systems in the depths of the oceans (not an environment known for its abundance of natural lighting) was still going strong – would we expect the first life to be photosynthetic?

    Furthermore the Venusian surface is not in darkness: according to results from the Soviet Venera 13 and 14 probes the light levels are around 5000 lux, which is comparable to an overcast day on Earth (~1000 lux).

  • Nick February 4, 2012, 14:51

    “would we expect the first life to be photosynthetic?”

    No, but without a good energy source we would not expect anything like the Cambrian explosion or subsequent developments. Even with photosynthesis, a hydrogen-rich atmosphere that prevents the accumulation of oxygen would also likely prevent this.

  • Rob Henry February 4, 2012, 16:49

    Amphiox wrote “And as for the so-called “astronomical complexity/improbability of the simplest known closed ecosystem”, astronomically complex COMPARED TO WHAT? Improbable WITH RESPECT TO WHAT?”

    This reflects the default biologists response through the ages that has been what looks simple must be. Von Neumann studied this ignored problem of non-trivial selfreplication in great depth, and found that even in an artificial mathematical system that was used to facilitate the task, the design was so complex that he could not give its detail, and had to be content with just proving that it was possible.

    Of cause that does not preclude the possibility that in some systems the task is much easier, or that we live in one of these, but don’t you find it a but suspicious that the simplest cell are immensely complex, or that with all our modern intelligence we cannot ever design (let alone build) a self replicating machine.

  • Rob Henry February 4, 2012, 20:39

    Nick, the available energy to an ecosystem is a very important problem. I am often puzzled when a scenario is given that would feed Europa’s ecosystem, but cap its biological activity at around one billionth Earth’s level (for example that it is fed by hydrothermally generated chemicals), and next a claim given that finding interesting higher forms there is also possible. This is not one of those cases.

    On Earth, only about 0.07% of incident light is captured into *dark reaction* energy that can then be used by life here. During *snowball Earth* that is said by many to be the progenitor of that *Cambrian explosion*, we might expect the available power to be a couple of orders of magnitude lower than it is now. Thus, unlike on Europa, there are still seem ample ways in which the ecosystem on GJ 667Cc could be sufficiently energetic.

  • Rob Henry February 4, 2012, 21:33

    Actually I might be able to put a MINIMUM cap on the power of a GJ 667Cc ecosystem if its atmosphere is methane dominated.

    At its very least this ecosystem would have to metabolise all the high energy compound that are generated by uv light high in its atmosphere, and these would otherwise accumulate on its surface. For Titan in our system the (geochemical??) process that do this equate 20W/sqkm, but if GJ 667Cc has our levels of uv light the problem must be 90X greater. From what I read here, incident uv levels are very much higher around red dwarfs. Say the factor by which they are greater at those two critical wavelengths that directly result in the photolysis of methane is W. Well the minimum power as a proportion of Earths is W/105.

  • kamal February 5, 2012, 4:19

    According to simulations, or closed-form solutions, what must be the orbits of moons around tidally-locked planets?
    1. Is it impossible to have satellites on tidally locked planets?
    2. Do the satellites get tidally locked (to the star) also?
    3. GJ667Cc was discovered by the RV method: isn’t it always possible (although disfavored by Occam’s razor) that such planets are double planets , summing up to 4.5 Earth masses ? (Or would double planets have a different RV signature than a single mass?)
    4. What is the maximum mass ratio that a satellite can have to its parent? I guess 1:1 if they are equal double planets?

  • Scott G. February 5, 2012, 13:01

    amphiox says:

    Without at least one other independent example [of the emergence of life] to use for comparison, IT IS IMPOSSIBLE TO SAY ONE WAY OR ANOTHER, NO MATTER HOW VAST YOUR KNOWLEDGE ABOUT THE ONE EXAMPLE YOU DO HAVE. …it MEANS ABSOLUTELY NOTHING with respect the questions of probability.

    Does it really mean ABSOLUTELY nothing? Can’t we extrapolate certain facts about the emergence of life based on our example, such as: that 2+ billion years of a habitable environment is not a REQUIREMENT for life to emerge, because it happened here in less time. Also, can you name one other thing that we have but a single example of in the universe (and don’t say the ‘Bing Bang’ itself, because that technically didn’t occur inside the universe)?

    PS – here’s a very cool video that illustrates The Evolution of Life on Earth in 60 Seconds.

  • Scott G. February 5, 2012, 16:22

    As a follow-on to my last comment… Can we not construct a ratio describing the rate-of-occurrence of life in our solar system (based on what we know) and apply that elsewhere? For example:

    Rate of Occurrence >= [Number of Occurrences] / [[Amount of Available Habitable Real Estate] x [Years that Real Estate Remains Habitable]].

    As an overly-simplified illustrative example, say that: Number of Occurrences = 1, Available Real Estate = 510,072,000 km^2 (the surface area of Earth), Years that Real Estate has been Habitable = 4 billion. Plugging in these numbers gives a rate of occurrence of life in our solar system of at least 4.357×10^-19 occurrences per square kilometer of habitable real estate per year.

    If we assume that our solar system is nothing special, then why can’t we apply this rate of occurrence elsewhere in the galaxy to give a prediction of the total number of occurrences of life in the galaxy?

  • Nick February 5, 2012, 21:41

    “If we assume that our solar system is nothing special”

    Sure, if you win the lottery today, you can safely assume that you’ll win the lottery every day. If you win the lottery in California, you can safely assume that you will also win it in New Jersey. Flawless reasoning.