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
Habitable zone around Gliese 667
Earth equivalent positions
3- Liquid water?
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.
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,
Therefore, further observations are needed to answer if GJ 667Cc truly supports liquid water and if the conditions on this planet are appropriate for
4- Close to the star
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 
5- A flaring host star - Speaking of magnetism
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.
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 belt
that 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.
edit on 20-2-2012 by elevenaugust because: resizing pictures!