Another Earth?

Interesting news on the astronomy front:

Orbiting a nearby red dwarf star called Gliese 581 are 6 planets. One of them is a rocky ball, bigger than Earth, in the "habitable zone" where water is liquid and temperatures are human-friendly. It's possible we could live there.

Unlike Earth, this planet called Gliese 581g, is "tidally locked" to its star. That means one side of the planet always faces the sun, and the other faces darkness. Temperatures on the two sides would be dramatically different, with the livable area in the "terminator" between day and night. Living on Gliese 581g would put you in an eternal twilight, which doesn't sound bad at all. Temperatures in the terminator area might be between -24 and 10 degrees Fahrenheit (-31 to -12 degrees Celsius), which is the average temperature of the planet's surface. So things would be a bit chilly, but if you could always visit the perma-sun on dayside if you needed a dose of red dwarf radiation.

This is only about 20 light years away. (Well 'only' is quite the word here. If we could travel at the speed of light it would still take a 20 year journey to get there. Moving at 1/100 the speed of light, which is much faster than we can currently go, it would take a mere 2000 years. Which is a lot. Still, in stellar terms this is pretty close.)
Ok, as I was saying this is only 20 light years away and it's interesting as it suggests that Earth-like planets might be plentiful. And every time we find one of these nearby planets we should devote some resources to studying for signals of population. This means radio, but it also means detecting methane and CO2.
This article does contain two of my pet peeves when it comes to exoplanet reporting. First of all, we have no idea if this planet is tidally locked. It was widely believed that Mercury was tidally locked with one side constantly staring into the sun while the other was believed to be the coldest spot in the solar system. Back in '65 we were finally able to train a radar on it and we discovered that it was indeed rotating.
The other thing that bugs me is the idea that we have some solid idea what the true temperature range is. All that we know so far is the distance from its sun and its mass. We don't know the atmospheric composition and that's a very important piece of the puzzle. We haven't been taking a global temperature of our own planet for very long and somehow we think that the process is mastered enough to give us absurdly precise estimates. Maybe we'll have instruments soon that can give us these figures but we don't have them yet.