Earth’s twin will be discovered in 2013, astronomers predict

[D Gary Grady]

10. And don't forget Venus

Curiously, a first-pass estimate of the expected temperature puts the Earth just beyond the habitable zone. We're warm enough for liquid water only because of the greenhouse effect (which in itself is a good thing; it's adding a lot of additional greenhouse gases that's the problem).

Venus is an interesting case: It's closer to the Sun and hence gets more intense sunlight, but its upper-atmosphere clouds make the planet more reflective by just about the right amount that all else being equal, the surface temperature on Venus would be similar to that on Earth, making for an environment perhaps even conducive to alien princesses in bikinis. Alas, Venus has such a super-dense, predominantly CO2 atmosphere that the greenhouse effect gives it a surface temperature of hundreds of degrees. (You can cook a turkey on Venus in like 20 minutes just by putting it on the porch.) Not good for alien princesses, dagnabbit. I haven't entirely give up hope for mermaids on Enceladus, though.