They also have a picture that I didn’t include in my original post, and it’s so good that I’m including it here:
Take a look at that. Two of the planets, Gliese 581 c and Gliese 581 d, are just on the theoretical edges of the habitable zone. And there’s a whole looooot of space in between them. In our Solar System, that’s not how it works. We don’t have a gas giant mixed in with the rocky planets, and we don’t have a gap the size of the habitable zone between planets.
Who wants to bet that there’s another rocky planet (or maybe more than one) in between planets c and d?