Gliese 581g: An extrasolar planet sitting in a "habitable zone"

Okay - so astronomers are getting close. Up until the mid-1990s, we did not have any confirmed detection of planets outside our Solar system. And now the number is close to 500 planets (and in the mean time we even managed to take away the planetary status of one of our own planets. Pluto is still a planet, Dammit! :) ). But then all of the detections were of planets much bigger than the Earth, with most of them orbiting close to their parent stars (this was mostly the consequence of the wobble detection technique being used - the parent star wobbles because of the tug from a big planet, orbiting close by).

Now astronomers have detected a planet, Gliese 581g, only three times the mass of the Earth and located smack in the middle of the habitable zone. Habitable zone only means that the planet is orbiting at a distance where water can potentially exist in liquid form. And water, we think, is essential for life.

Very cool! We are not talking about any intelligent lifeforms here - but simply the potential of simple life (though, of course, it would be absolutely amazing if there was complex life there - but we can't say any thing about it from the information we have).

Couple of quick things: This is the sixth planet discovered orbiting the star Gliese 581 (yes, such names are very sexy for astronomers) - in fact this is the most planets discovered (so far) around a star other than the Sun. Gliese 581 is located only 20 light years form us or about 200 trillion kms (crap - it sounds much closer in light years - so lets stick with that).

But here is the cool thing (literally). Gliese 581 is a red dwarf - which means that it is relatively cooler than the Sun (couple of thousand degrees on the surface, versus 6000 degrees for the Sun). The newly discovered planet, Gliese 581g, is quite close to its parent star and it takes only 37 days to make one full orbit. One consequence of this is that the planet is tidally-locked with its star - i.e. the same side of the planet always faces the star and the other star never sees any light from the star (our Moon is tidally locked with the Earth - this is the reason we only see the same side of the Moon from the Earth - and thus Pink Floyd could come up with their cool album name).

Here is a schematic of the habitable zone before the discovery of Gliese 581g. It would sit smack in between the planets c and d:

So can there be life on a planet - where there is perpetual light on one side and perpetual darkness on the other? Very hot on one side and very cold on the other. We don't know (yet). Some have speculated that the border between the shadow and light may be a good place for life to originate and evolve. One can also imagine local terrestrial features, such as mountains, cracks, or crevices that may shield organisms from the blazing heat and may provide a suitable environment to thrive.

Okay, we'll have to eventually take a field trip there. But this is certainly the first of many planets discovered that will be good candidates for hosting other lifeforms.

Read the press release here and a story from the Washington Post here. If you are interested in Gliese 581, you can more information here.