DanielC

Hello, I'm new in this forum. I just thought this thread and I thought I might reply. I am currently doing a masters in astrophysics and I'm very interested in exoplanets. There is a difference between "equilibrium temperature" and "surface temperature". Earth's equilibrium temperature is 255 K which is also below freezing. More interesting is the surface temperature. For Earth that is 288 K and for Gliese 581g the current guess is about 247 K. That's still below freezing, but it is not nearly as bad as it sounds. For reference, this value puts the planet's temperature right in the middle between Earth and Mars. We know that Mars once had liquid water, so Gliese 581g probably has/had water. Furthermore, what went wrong with Mars is that it was just a bit too far from the sun and it didn't have enough gravity to hold on to its atmosphere. Gliese 581g doesn't have either of these problems, so it's a pretty exciting candidate. If you can, read the paper by Joshi, M. 2003 Astrobiology, 3, 415. He did a climate simulation of a tidally locked planet. His main finding is that they'd actually be quite habitable. As long as it has a decent atmosphere and and active hydrology, the temperature differences between cold and warm parts are not too extreme. Basically, the more water the better. So, for example, if Gliese 581g has a very deep ocean, I wouldn't worry much about libration. Earth plants need a day/night cycle, but there is no fundamental reason why alien plants have to be like that. Evolution makes life adapt to whatever conditions are prevalent in the area. I'm not a biologist, but I'd imagine that not having a night would not be much of a bother for Gliesean flora. I imagine that Gliesan astronomers are ignoring big type G stars because obviously a planet with a day/night cycle could not support life No Kepler. Yes, this was discovered by wobble. Kepler should deliver similar discoveries in a couple of years. AFAIK Kepler's field only includes pretty far away stars. Actually, it is the 116th star. Wikipedia is wrong on this one. The paper I mentioned earlier (Joshi 2003) does not predict very strong winds at the border. It actually predicts the strongest winds at the substellar point (where the star is straight up). His paper assumes a planet somewhat warmer than Gliese 581g and it predicts mean wind speeds of 15 m/s, which is a strong wind, but it's not a hurricane. We don't have the technology to photograph a planet like this. In 8 years, when the E-ELT comes online we'll be able to photograph these planets - and by that I mean that we'll have one pixel or two. That will be a very cool time because when we can get a pixel of light from a planet, you can do spectroscopy and figure out what the atmosphere is made of. And if it is very far away from chemical equilibrium (like ours) that would be a tell-tale sign of life. Actually, that's not the problem. The problem is that it is right next to something really really bright. If the model from Joshi is valid (see above), the winds will not be particularly strong. The strongest winds are in the hottest spot, and with an average of 15 m/s. And that model was assuming an Earth-like energy flux. Since Gliese 581g is colder than Earth its winds would be correspondingly slower than that. According to Joshi's model, yes. His models included both a water world, and a half-water / half-land world. Both were habitable, but the water world had a better climate (not surprising).