When you're homesick, you start seeing traces of home everywhere you look.

When I went away to college, my heart would skip a beat every time a particular Ford Escort drove by, because it was the exact same model my best friend from home drove--even though I knew she was five hundred miles and four states away.

At one of my first jobs after college, I felt a surge of affection for the building custodian just because he was a dead ringer for my dad--from thirty feet away, if you stood at the right angle, and if he was wearing his glasses.

And here on Earth, we see--or think we see--planets that look like home when we look out into the cosmos. In this case, "looking like home" means having a solid surface and the capacity to support liquid water. It doesn't sound like much to ask, but in fact finding such planets with today's technology is like reading the very last row of the eye chart at the optometrist's office--possible, but just barely. Of the 600 or so known exoplanets, only a handful could maybe, possibly, be capable of supporting life.

An artist's impression of the potentially habitable planet orbiting the Sun-like star HD 85512. Credit: ESO/M. Kornmesser.

Now, astronomers have announced the discovery of a new planet that just might fit the bill. It's 3.6 times the mass of Earth and orbits at the inner boundary of the habitable zone--meaning that it is hot, but (with enough cloud cover) perhaps not so hot that water would vaporize. The planet, called HD 85512 b (because it is in orbit around the star HD 85512), was discovered using the HARPS spectrograph at the La Silla Observatory in Chile, which enables astronomers to track the gravitational wobbles that planets induce in their parent stars. It was announced along with a batch of 49 other exoplanets. (For more on how this technique works, see NOVA scienceNOW's Hunt for Alien Earths.)

Though scientists who discovered the planet are calling it "the best candidate for exploring habitability to date," it isn't the first potentially habitable planet we've found. Back in January I wrote about a planet called Gliese 581 g, which could be habitable--if it actually exists, which is controversial. And Gliese 581 g followed a string of other false alarms.

That's not to say that we shouldn't be excited about this new discovery--just that we should be cautious before, you know, running across the quad with our arms outstretched to give it a big hug, only to realize that it isn't quite who--or what--we thought it was.