Gliese 667Cc: A new ‘Super-Earth’ basking in the light of three Suns

Astronomers announce with excitement the latest exoplanet found to be orbiting within the habitable zone of its star. In addition, the newly discovered Gliese 667Cc is a member of a very unique orbital system. Its parent star, the red dwarf Gliese 667C itself orbits a binary system of two K-type stars, Gliese 667A & B at an enormous distance roughly equivalent to 6 times that between the Sun and the dwarf planet Pluto. Accordingly, the distant binary system, whilst bound gravitationally, has no affect over the planetary environment of Gliese 667Cc, nicknamed ‘Vulcan’ by astronomers after the triple-star system home to Star Trek‘s Spock. I’m not much of a sci-fi fan, despite my interest in all things exoplanet, so I’ll stick to an shortened ‘Cc‘ for brevity.


The Gliese 667C system revolves around a M1.5V red dwarf, a small star only 31% as massive as the Sun and much less luminous, located 22 light-years away from Earth in the constellation Scorpius. The habitable zone extends from 0.11 AU out to 0.23 AU, well within the orbit of Mercury if superimposed onto the Solar System.  Cc has a minimum mass equivalent to roughly 4.5 Earths and orbits at 0.12 AU, straddling the inner edge of the habitable zone. Accompanying Cc in orbit is Gliese 667Cb, a large (5.7 Earth masses) planet nestled at 0.05 AU, and possibly another planet of equal mass, dubbed Gliese 667Cd, at 0.24 AU.

Gliese 667 Cc performed very well in a habitability assessment undertaken by the Habitable Exoplanet Catalog (HEC), ranking as the planet with the greatest habitability potential of all discovered exoplanets to date:

Habitability assessment of Gliese 667Cc by the Habitable Exoplanet Catalog (information and graphics by HEC, 2012)

Figures in red are subject to large uncertainty, and will only be refined with more detailed observation. A quick refresher of the HEC metrics in the context of Cc: ESI is the ‘Earth Similarity Index’  and consists of several planetary characteristics, namely radius, density, escape velocity, and surface temperature that are used to determine the relative similarity of the planet to Earth on a scale from 0 (completely dissimilar) to 1 (identical). An ESI 0f 0.82 represents an ‘Earth-like’ world, but the large mass (5.2 as the mean expected mass) of Cc has negatively affected this value.

SPH is the Standard Primary Habitability, a measure (from 0 to 1), calculated from surface temperature and humidity, of the ability of the planet to support terrestrial primary producers. In the case of SPH, Cc outranks even the Earth! Its position half-way between the very centre of habitable zone and its inner edge, represented here by the metric HZD, means that it is extremely favourable to supporting a ecosystem of primary producers similar to those on Earth. However, as a red dwarf, Gliese 667C emits much of its radiation in the red, near-infrared (NIR) and infrared (IR) portion of the electromagnetic spectrum. Red dwarfs like Gliese 667C are also known to be more variable and prone to flaring.  The affect of this shift in wavelength would have very negative repercussions for Earth-based photosynthetic mechanisms which utilise visible light, but the possibility of photosystems evolved to exploit lower-energy NIR/IR radiation is hypothetically possible.

Other values to note are the comfortable planetary temperature of 29 °C, large mass and somewhat more suppressive gravity. A year on Cc lasts 28 days. Unfortunately, it isn’t possible to determine whether Cc is a rocky, watery or gas planet without an accurate measurement of its size, a parameter still unavailable at this stage. The effects of a possible atmosphere cannot be accounted for just yet but a thick greenhouse of water vapour, carbon dioxide or methane would elevate the planetary temperature beyond that considered habitable.

Lack of public interest

So it seems that Cc  is the new champion of the habitable planet competition being held by scientists on Earth, and the evidence seems to back up their claims. Why then the lack of public interest? Outside of popular science websites and publications, news of this new planetary utopia is hard to find. Contrast the scarcity of coverage with the hype surrounding Kepler 22b two months ago, and I fear the predictions I made in these posts may have come to fruition. The wider public is bored; they’ve heard it all before and become desensitised our disinterested. Kepler 22b is habitable, so is Gliese 581d and now so is Gliese 667Cc. It’s disappointing, but inevitable, that the furore of excitement surround these planet discoveries wasn’t sustainable. The thing is, we still haven’t stumbled across the perfect Earth analogue, a replica of our watery, rocky globe. Yet. We will do, and when this day comes and the discovery is announced, I fear the room may be empty save for a few dedicated science correspondents that realise the very real implication of finding a planet like this.

Update (08/02)

It seems that in my haste to bemoan the lack of mainstream press coverage of Cc, I neglected to detect the underlying politics of the announcement. The main reason that Kepler 22b attracted so much more attention is that Cc was not announced by NASA. The NASA PR machine is an effective beast. Also, the discovery of Gliese 667Cc was first announced last November by a European team of astronomers led by Xavier Bonfils from Université Joseph Fourier in Grenoble, France. However, it’s confirmation came yesterday from an international team lead by two American astronomers, Guillem Anglada-Escudé and Paul Butler from the Carnegie Institute for Science. Cc‘s discoverer is therefore under debate.

The coverage of Gliese 667Cc also seems to suffer from a somewhat of a geographical disconnect. Daniel Fischer, who runs the excellent ‘The Cosmic Mirror‘ site, notes that the coverage of Cc has been extensive in his native Germany because of Anglada-Escudé’s link with the University of Göttingen. Parodies and further analysis can be found here and here, respectively (in German – thanks Google Translate!).

It seems that the story of Gliese 667Cc is far from over.


32 comments on “Gliese 667Cc: A new ‘Super-Earth’ basking in the light of three Suns

  1. Hi, The public isn’t bored else I would not read your article. Consider how technically written your article is and how few people will eventually get excited over that not mentioning that they are hardly able to convert your story into something imaginable. Show us a picture of any exoplanet and keep out the tech words and you have a ballgame. We not are all astronauts or do have a degree in astrofysics. For the public there are too many “buts” and “unfortunalies”. For the rest you might describe also what you understand with “life” so the “public” might also get a glimpse of that. Furthermore maybe explain also a bit more in everday words what conditions really are neccesary for a alien planet to harbor “life”. For instance without the famous greenhouse effect here on earth than we would have an average temperature of -18 degrees celcius. And we are in the habitable zone. This is just some example of the many variations you can add to this that an exoplanet would need to sustan “earthalike” life or life as we know it.

    • Hi Tjapko, thanks for reading and for the comment. It’s very difficult to describe a new exoplanet without putting into the astronomical context; to do that it is necessary to invoke some of the more complex vocabulary associated with the field. I try to keep it simple where I can, and I’ll try to improve this in the future. In many previous posts, for example this one, I’ve tried to cover some of the basics of planetary habitability. The reason there are so many “buts” and “unfortunately”s is because of the extreme uncertainty involved in this area. I write as if the existence of these planets are written in stone, but we have no pictures to show or even faint satellite images to accompany the find; all the methods are complex and indirect, despite their brilliance. I worry that the wider public will get bored of these stories before I REALLY good planet comes along, and that would be a travesty, which is why I err on the side of caution. I wrote about that in the linked article above.

      • The local gravity is also deeendpnt on the size of the planet, since this one will most likely be larger than Earth (though not that much more), your weight will be less than 7 times Earth normal, though most likely still much higher than here (if the planet is only 1.2 times the radius of Earth for instance, local weight will be about 5g’s)But yes, Kepler has found a lot of potential candidates, and will continue to do so. Not sure if the James Webb is doing any dedicated planet hunting, but I guess the data could always be used to look for candidates.

  2. Andrew,
    I don’t know what the public thinks, but I think, generally, the folks who report on exoplanets tend to be “believers” in the truth of extra-solar life. So, the articles are effusive and gushing with hopefulness. But, the reality is that a life support planet needs more than the things we focus on. A planet which is tidally locked is really not a great candidate, Maybe in the twilight zone you have a chance to sustain life, but life still needs to originate.

    But, the atmosphere can be a real killer. Why do we have 20% oxygen? Because oxygen generating bacteria originated (were created?) on the earth 3.8 billion years ago. It took them billions of years to remove a lot of CO2 so that earth could support advanced life. But, in the absence of early life to make a planet habitable by transforming atmosphere, the greenhouse effect runs away and makes it so hot life can never form. Global warming is caused by an increase in the tenths or hundredths of a percent of carbon in our atmosphere. But, Mars and Venus have almost no free oxygen and lots of CO2 and they are more likely models than Earth.

    Then, we currently measure a star’s metallicity which is the Fe/H ratio. But a more important measure might be for carbon. Not as easy to measure as iron. Is the metallicity measure a good proxy for all the necessary elements? I don’t think so. Look at Io. It is incredibly sulfur-rich. What does that do for make a good life-support planet? If we found a G-type star with a metallicity of zero and a planet the size of earth in the habitable zone, it could be like Io.

    Have you ever considered the need for Uranium and Thorium to keep plate tectonics going? In the absence of plate tectonics, a planet becomes dead – no recycling.

    Have you ever calculated what would happen to Earth if we had 10% more water or 10% less? We are concerned about coast lines when a the ice caps melt. What percent of the water on earth is that? What are the chances that a planet has the right amount of water. Look at Enceladus.

    Extra-solar life enthusiasts should run the numbers a little more. I have seen a list with over 800 factors that can affect the habitability of a planet. Some are critical to advanced life only but most are important for life at all.

    I know I sound really negative. But, for me, the question is where you put your hope. The high improbability of finding a life support based on the statistics suggests that a guiding, caring Hand gave us a planet we can be thankful for.

    Have a great Earth Day – coming up soon,

    • Don’t be too critical. It may have a thick atrmephsoe for having 2 earth gravity than distributes heat evenly like venus.Because of a thick atmoshere the polar and night are dont go less than 10 degrees from daytime high. plus life is very tough and thrives places on earth once thouth impossible.The humidity of that planets pretty great so land life will be hard but hydrogen is the best radiation asborber.

      • We do not have %20 oxygen because bacteria made it, we did not lose CO2 because bacteria or planets consumed it. You sir are ignorant fool and have no saying on this matter. Go back to your farm and keep grazing like a useless lifeform you are.

      • Gordon,

        If you could please show a bit more respect when posting comments that would be appreciated. I encourage active participation and feedback on my site, but ad hominem is not welcome here, or in science generally. Your comment didn’t really add anything to the conversation as it doesn’t really make any sense in its current form. Please post a polite clarification if you sincerely want to enter into this debate.

  3. Pingback: Enough Time for Life: Part II | the II-I- blog

  4. Pingback: Recent Posts | the II-I- blog

  5. Gordon,
    Your rudeness makes you less useful. But, perhaps you could educate me. What did cause the earth’s initial oxygenation event if not the initial anaerobic bacteria?

  6. i agree with you Mr Anonomous. Gordon sounds like a cheeky little shitaki. u wont like me when im angry. By the way ive been to gliese 667c . ITS COOl

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