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Comment by hugh3 | Hacker News Reader

This is exciting, if not surprising, news. We knew that potentially habitable planets must be out there somewhere, but I'm still very excited that we now know where the first one is.

Expect to hear the name "Gliese 581g" a lot more in the future, because this will be the standard hypothetical nearby life-bearing system people will be talking about for years to come. Habitable and only twenty light years away?

The tidally locked nature of the planet is a bit of a bummer, though. If there were water on the surface, I wonder what would happen to it. Will there be a liquid-water ring, or will the water inevitably wind up getting stuck on the cold side, never to remelt? Perhaps a constant system of glaciers flowing from cold side to hot side, melting, blowing to the cold side and snowing down again?

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It's pretty unlikely this will remain highly talked about after Kepler releases its findings in a few months. Preliminary results show huge numbers of small earth-like planets. I believe they expect to find dozens or hundreds in the habitable zone. Kepler is really what everybody is waiting for and should completely revolutionize planet-finding.

Actually, the most interesting results won't be here til the second half of 2012, if you take the following [somewhat chauvinistic] criteria into account:

- A really interesting planet orbits a planet similar to the sun.

- The goldilocks zone around a planet similar to the sun puts it in an orbit radius of around 1 year (give or take 20% or so) because orbit period is a function of solar mass and distance.

- It takes three occurances to be sure that a "dip" you see in light emissions is probably a pattern rather than a coincidence. It's like colinear points on a plane: two points always make a line, but for three points to be on a line you're pretty damn lucky.

- Kepler was launched in 2009.

So in the end of 2012 we'll have a list of (hopefully hundreds of) confirmed earth-like planets that orbit sol-like stars with a rotation period around 1 year. That is awesome.

The way I see it, a tidally locked planet is an easier find, because of the high variance in surface temperatures. Relatively rotating planets will have far narrow variances, making most of them uninhabitable based on temperature.

I'm sorry how does the variance in surface temperature help us find it?(especially with current technology). As I understand it pretty much all the exoplanets so far have been found using Doppler shift. The size of the planet, more precisely the mass, and its distance from the star would influence the magnitude of the shift and hence detectability.

It doesn't help you find it. What it does is widen the acceptance criteria.

Instead of needing to find a rotating planet exactly in the "Goldilocks zone", any planet whose surface is hot on one side but cool on the other, such that the range of temperatures in some part of it lies in the zone, is acceptable, because you can suppose a zone of habitability on the edge of light and shadow.

I'm guessing that's easier because if the planet is a bit too hot on average, you can shift the zone into the shadow; and if it's too cool on average, you can shift the zone into the light. If the planet rotates, you've got a bigger problem, especially if it's too hot, because you need to find / build shade.

I guess a bigger bummer would be if the planet's core doesn't rotate. Apparently, it's the Earth's rotating molten iron core that generates the magnetic field that protects us from harmful radiation.

I hope we don't hear "Gliese 581g" too much. I think a proper name is in order.

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