Jingszo !

We now know that 1 in every 4 stars, at least, has a planet that is the same size as Earth and is rocky, and is the same temperature as Earth, so it's what we would call a habitable-zone planet. Those are very secure conclusions.

The next step is identifying biosignatures—chemicals in a planet's atmosphere that could only be there because of biological processes. Charbonneau says that the necessary evidence faces a major technological hurdle: It requires far more data than our current instruments can provide.

There's still the question of just how common life, let alone intelligent life, really is. It's possible, Charbonneau said, that if you take any habitable-zone planet, add water, oxygen, nitrogen, and phosphorus, and give it about a billion years, life will develop. Or you could have those very same conditions, and it would all remain stubbornly lifeless. You only have to look at the first habitable planet to have a much better idea how common life is.