Re: On Gliese, isn't it possible to live with these kind of conditions?

Mike,

Thanks for the question.  You have been keeping up with the latest 
developments in extrasolar planets.  Certainly Gliese 876b is one of the 
more interesting ones out there.

First let us put the known facts on the table.  The star is Gliese 876, an 
M class dwarf about 1/3 the mass of our Sun, and about 1/40 as luminous as 
our Sun at a comparable distance.  The planet is Gliese 876b, discovered 
just a couple months ago through careful measurement of the Doppler shifts 
in the star's light.  While the planet was not seen directly, we are fairly 
certain it is there.  It orbits about 0.2 astronomical units from its star, 
it is 5 times closer to its star than the Earth is to the Sun.  Its orbit 
is fairly elliptical, with e = 0.37, which means that it is about twice as 
close to the star at its closest (perihelion) compared to its furthest 
distance from the  star, aphelion.  The planet is estimated to have a mass 
about 600 times that of Earth, or slightly less than twice the mass of 
Jupiter.

Since the astronomers do not directly see the planet, they used a 
calculation based on light absorption to find the temperature of the 
planet's atmosphere at the point where it is getting cloudy enough to 
absorb the light.  This is where the 198K figure comes from.  The 198k 
figure does not mean that this is the constant temperature.  Gliese 876 
appears 4 times as bright when the planet is at perihelion compared to 
aphelion.   Also, there is at present no way to know about the internal 
heat of the planet itself.  If it is fairly young, about a billion years, 
its temperature may still be hotter than 198k since it would retain heat 
from its formation.  

It is very probable that Gliese 876b is a gas giant without a solid 
surface.  It might be possible for people to live there on floating balloon 
structures, but even though the temperature is on the margin of liveable, 
there are many other problems.  The atmosphere is probably mostly hydrogen, 
which is not breathable, and in fact is very flammable with oxygen.  People 
would have to live in sealed chambers, and be very careful not to let the 
outside atmosphere into the living environment.  Also, the planet is bigger 
than Jupiter, so the gravity is probably at least 3 times Earth normal.  
People could not do much walking or lifting there.  Finally, the extreme 
change in solar radiance as the planet orbits probably makes for extreme 
weather changes.  

Some of the negatives of Gliese 876b would be avoided if it has an Earth 
sized moon orbiting it.  If Gliese 876b is too hot, a satellite planet 
would probably be cooler.  Also, the gravity might be Earth normal or even 
less, and there could be a solid surface to stand upon.  Finally, there 
might be a chance for an oxygen atmosphere, so the space travelers would 
not have to worry about going up in a puff of flame.  I think such a 
satellite of the planet would be a much better place to try to live than 
Gliese 876b itself.

Regards,
Everett