From the link in the o.p.:
*Gliese 581g, as the new planet is called, is in the zone where the temperature is just right. And with a mass of just three times that of the Earth, it’s unlikely to be a gas giant.
However, this does not mean the planet is habitable, or even very Earthlike. It may not even have any water on it at all. For now, we can’t know these things, so beware of any media breathlessly talking about life on this planet, or how we could live there.
There are some things we can speculate on with some solid footing. The orbital period of 37 days puts it pretty close to the star – since the star is a red dwarf, it’s cooler than the Sun, so being closer doesn’t necessarily mean you overheat. But it does mean the star exerts strong tides on the planet, which have the effect of slowing the planet’s rotation until it equals the orbital period. This has almost certainly happened to this planet, so in other words, one day on this planet = one year, and the planet always shows the same face to its star like the Moon does to the Earth.
That makes things a bit dicier for habitability. The side facing the star may get very hot, while the dark side gets very cold. If the planet has an atmosphere that gets mitigated somewhat (the hot air on the day side will flow over to the night side and vice versa, smoothing out the highs and lows in temperature), and may make the planet more clement. However, **we have no clue if this planet has an atmosphere at all.***It is somewhat premature to even attempt to guestimate the probability of life, much less assign it a likelihood of unity. Gliese 581g has been known for several years and I don’t see that this presents any new information, but Vogt is likely correct that such worlds are at least not uncommon, at least in the context the trillions of planets orbiting the estimated 200 billion stars in our galaxy. Even if an ‘Earth-like’ planet (rocky, in the orbital zone for liquid water, has an atmosphere) is only found around one out of a thousand of M, K, and G stars, that is still likely hundreds of million potentially habitable worlds.
However, we should not assume that rocky worlds which could support surface water are necessarily habitable, particualrly if they are orbiting flare-prone red dwarf stars, and what is habitable for us is not necessarily the ideal medium for life; there is a growing body of thought that if chemical life is common (and given that our organic chemistry is based on the most common chemically reactive elements in the universe) that large moons with hydrocarbon atmospheres like Titan or subsurface liquid oceans like Enceledus or Europa, driven by tidal heating, may be more stable and amenable to the formation and evolution of life.
This is ‘interesting’ but not proof of anything, and I look forward to the as yet undiscovered and far stranger plaets and potentially habitable environments that we have yet to observe that may be beyond our imagination.
Stranger