Life on Gliese 667Cc: is it really possible?

In a previous thread, I showed the last update of the Habitable Exoplanets Catalog Project from the Planetary Habitability Laboratory that identifies and rank potential habitable exoplanets from both confirmed and unconfirmed exoplanets.

Actually, we all know that the best candidate for hosting life is Gliese 667Cc (also called "GJ667Cc") which is the second Planet orbitting Gliese 667C (a red dwarf star of spectral type M), 22.1 light years away from earth.
The minimal mass of this planet .012 jupiters or 3.9 earth masses, which would make it a super earth.


Artist view of Gliese 667Cc

Now that more and more discoveries have been made in recent years (more than 700 exoplanets are known, while over 2000 candidates wait for confirmation), the increasing number of known potentially habitable planets suggests that such planets might be frequent in the universe.

But what are the necessary and/or useful conditions for GJ667Cc for really be able to hosting life?
Let's see these in details now.


1- Host star

In all the existing spectral type of stars, there are some that are particularly common in the universe: red dwarf star of spectral type M., also called “M-dwarfs”, that are smaller and cooler than our Sun but make up at least 60% of all stars.
Most stars that host exoplanets are thus expected to be cool M-dwarfs, which makes the case of GJ667Cc particularly interesting.

With an effective temperature of 3400 °C on its surface, the host star GJ667C is much cooler than our Sun, which has a surface temperature of 5500 °C. This red dwarf star therefore emits much less radiation than the Sun, reaching a luminosity of only just over one percent of the solar value.


Relative star sizes


2- Not too hot and not too cold

The habitable zone around a star is defined such that the temperatures on the surface of a planet are just right for water to exist in liquid form. Liquid water is considered to be one of the most essential requirements for the formation of life.
The Earth is located in the habitable zone around the Sun at a distance of 1 AU (astronomical unit). Owing to the much lower energy output, the habitable zone around the red dwarf star GJ667Cc is much closer to this star at distances between 0.11 AU and 0.23 AU. The Earth would be an iceworld if it orbited this star instead of our Sun. Fortunately, the planet GJ667Cc is located eight times closer to its star (at 0.12 AU), which puts GJ667Cc comfortably into the habitable zone.

Habitable zone around Gliese 667


Earth equivalent positions


3- Liquid water?

Most of the radiation flux emitted by Gliese 667 is in IR, which is most likely enough to allow the existence of liquid water at the surface of GJ667Cc. That makes around 90% of what we receive here, on our Earth, from our Sun.
However, the surface temperature is uncertain and depends of several factors, such as atmosphere composition and weight, existence of a magnetic belt, etc....
Therefore, further observations are needed to answer if GJ 667Cc truly supports liquid water and if the conditions on this planet are appropriate for hosting life.


4- Close to the star

Due to the short distance to its central star, GJ667Cc orbits this star in only 28 days. One year on this planet is thus only 28 Earth days long. This would make it possible to celebrate your 1000th birthday (which is just 77 years on Earth). The days, however, could be very long.
As the planet is so close to its central star, it is very likely that the planet is tidally locked. It would rotate synchronously and show always the same side towards the star – an effect that we know from our Moon. Consequently, there could be eternal day on the hemisphere towards the close-by star and eternal night on the other side, which is facing outer space. The temperature differences between both sides could be large and could affect the global climate.

The Sun seen from Earth (left) and an impression of how the red host star could look from the surface of the planet Gliese 667Cc (right). see note [1]


5- A flaring host star - Speaking of magnetism

Many M-dwarf stars are known for emit intense bursts of radiation and energetic particles (flares) that can drastically increase the brightness of the hosting star in minutes. They can be a thousand times stronger than those that come from our Sun.
However, around the Earth, there are the two Van Allen radiation beltthat protect us from the higher energetic particles coming from sun flares, but unfortunately there are no datas to confirm whether the same kind of belt exist around Gliese 667Cc or not.


Laboratory simulation of the Van Allen belt's influence on the Solar Wind

Another problem is connected to the presumably strong magnetism of the star. Many red dwarfs may be often covered by starspots (the analogues of sunspots) that could reduce the energy output of the star by as much as 40% for periods that may last months. Together with the fact that the red dwarf star emits almost no ultraviolet light, these varying light conditions could be a potential problem for the formation of life as we know it.


6- Living on GJ667Cc – a heavy experience

The mass of the planet GJ667Cc is estimated to be (at least) 4.5 times that of the Earth. Like Kepler-22b, GJ667Cc is a Super-Earth, i.e. a planet that is slightly larger and heavier than our Earth. The size and density are not known yet which leaves the possibility that GJ667Cc after all could be an inhabitable gas planet. Only a more compact rocky or ocean planet with a corresponding radius between about 1.7 and 2.2 Earth radii would be favorable for the formation of life.
The higher mass of this planet, which we assume to be rocky hereafter, results in a gravitational acceleration (that’s what keeps us on the ground) on the surface that is about 4.5 times higher than compared to Earth. In other words, you would feel 4.5 times heavier. A person with a weight of 75 kg on Earth would thus weigh a remarkable 340 kg on the Super-Earth. This weight is close to what one experiences during heavy acceleration in a high-g roller coaster – only permanently. Long walks and stepping on the scales would probably be rather unpopular on GJ667Cc.
Furthermore, a heavier planet can keep a more massive atmosphere. Consequently, the atmospheric pressure at the planetary surface is likely to be higher. If GJ667Cc has an atmosphere that scales proportional to the terrestrial one, then the pressure would just be a few times higher. For a more extreme case like a Venus-type atmosphere, the pressure could be several hundred times larger, which corresponds to a water pressure a few kilometres deep down in the ocean on Earth.

7- Conclusion: could there be life?

Although GJ667Cc is located in a habitable zone, the conditions on the planet could be very different from our Earth. Life would be facing some potential challenges, which may include low and varying light conditions, possibly a higher atmospheric pressure, and violent flares.
Nature proves to be inventive though. Even on our own planet we find species that show an amazing ability to adapt to extreme conditions. Examples are the so-called tardigrades, which are also known under the charming names “waterbears” and “moss piglets”



These tiny creatures range in size from just 0.1 mm up to 1.5 mm. They are found in hot springs, ocean sediments, under ice sheets and even on top of the Himalayas. Waterbears tolerate extreme temperatures from just above absolute zero (-273 °C) to about +150 °C. They can survive years without water and a 1000 times more radiation than other animals. These hardened creatures have even been returned alive from studies in low earth orbit where they were exposed to space conditions. Even if the conditions on GJ667Cc might not be favourable for most terrestrial life forms, it certainly leaves room for the imagination. We can only speculate how fauna and flora – if present at all – would evolve under such different conditions.

Credits goes to researcher Sven Wedemeyer-Böhm


7- SOURCES

Institute of Theoretical Astrophysics
A planetary system around the nearby M dwarf GJ 667C with at least one super-Earth in its habitable zone
The HARPS search for southern extra-solar planets XXXV. Super-Earths around the M-dwarf neighbors Gl433 and Gl667C
Chandra chronicles: What to Look for in Red Dwarf Real Estate
Habitability of red dwarf systems
Van Allen radiation belt
For Alien Life-Seekers, New Reason to Hope
HEC: Graphical Database Results

Great thread! Excellent use of diagrams and explanitory information.

My opinion is that life should florish throughout the universe. I feel however, that not every planetary system is a possible host.

I can imagine many different beings that could evolve on Gliese 667c under such conditions though.

We live in extraordinary times-and soon I hope to see spectral lines from these worlds...showing evidence of water and oxygen too.

Thank you for a well put together and easy to read thread.

I always get so excited with this stuff. Thing is, I am an impatient person and I want to see us as a human race go to these places...which may not happen for a long, long time. =(

Originally posted by Sundowner
Thank you for a well put together and easy to read thread.

I always get so excited with this stuff. Thing is, I am an impatient person and I want to see us as a human race go to these places...which may not happen for a long, long time. =(

Thank you!

Well, you never know... Remember the movie "Contact" where distance wasn't a problem to travel from star to star.
Humankind is full of resources!

Very great thread, star for you.

I have a very wide imagination, so I already have some great ideas on what kind of creatures could live on planets like this. What I'm worried about though is what will humankind do if they find life on other planets? I'm even more worried how humankind will act if the find "intelligent" life.