Newly discovered planet Gliese 581g - just a few times the mass of Earth, average surface temperature a balmy minus 31 to minus 12 C, not too far away...

It turns out the red dwarf star Gliese 581 has two more planets on top of all the other interesting ones we've discovered and talked about, and one of them is a prime candidate for our first Earth-like planet. There are a lot of articles on the planet but the best source is almost always Bad Astronomy, where we get some commentary along with it.

What we know about this planet so far:

- Mass is at least three times Earth (probably three to four times), and depending on the size its surface gravity could be not too much greater than ours.

- Orbital period 37 days

- Average surface temperature some -31 to -12 C. This could vary quite a bit depending on atmosphere.

- Almost certainly tidally locked.

In other words, (assuming there is dry land there) it looks like this is a planet that we could visit and walk around on. The atmosphere could be poisonous, atmospheric pressure is unknown, but if we are lucky then it could be a place that we could potentially just set up shop on and begin exploring...if we could just cross the 20 light years it takes to get there in the first place.

By the way, Gliese 581 has a radial velocity of -9.5 km/s, so however slight it's nice to know that it's moving towards us bit by bit. That means over the past three decades it has moved 9 billion km in our direction, or 60 AU (twice the distance to Neptune).

Wikipedia has a page on the planet here, and expect it to grow in size over the next few days. Other articles on the discovery are here, here, here, and here, among others. Expect there to be a lot of discussion on this planet in the next few days.

Edit: here's a video on the discovery too.