Scientists have discovered a so-called "Goldilocks" planet with a temperature that is not too hot, not too cold, but maybe just right to support life. Correspondent Spencer Michels reports.
JUDY WOODRUFF: Finally tonight, scientists on the hunt for an Earthlike planet.
NewsHour correspondent Spencer Michels has the story.
SPENCER MICHELS: More than 20 years ago, space scientist William Borucki dreamed up a plan to explore our galaxy to find the extent of life, if there is any, beyond the Earth. It was a daunting and expensive challenge.
This week, and $600 million later, at a conference of his peers in Mountain View, Calif., Borucki and NASA announced they had found the first planet in the habitable zone. That means what's being called the Goldilocks planet is just right, orbiting its star at the proper distance to have water, necessary for life.
Similar to Earth, though bigger, scientists say the temperature averages about 72 degrees -- 600 light years away, it orbits its own sun every 290 days. Borucki and his team found it using the Kepler space telescope, which was launched three years ago and remains in orbit around the sun.
He calls it a giant camcorder which was designed specifically to look for planets where life might be possible, and at the stars they orbit, 150,000 of them, much like our own sun.
WILLIAM BORUCKI, NASA space scientist: The mission was designed to do this job. It has no other purpose.
SPENCER MICHELS: I talked with him at NASA's Ames facility on the grounds of Naval Air Station Moffett Field about how Kepler can detect a planet.
WILLIAM BORUCKI: We look at each star to see, did something dim the star? Did something move across the star, dim it? If it dims the star a lot, it's a big planet, just a little bit, it's a small planet, maybe like Earth. So it's focused on one set of stars in a part of the Milky Way where there's a huge number of stars.
And it just takes a photo every six seconds.
SPENCER MICHELS: Scientists have found more than 2,000 candidate planets in the two years they have been looking, and 48 that they think could hold life. But this latest one, Kepler-22b, as it's called, is the most promising so far.
Was there ever kind of an aha moment, when you knew something was really important?
WILLIAM BORUCKI: Yes, there was. I was just delighted to see that data come down.
It's a feeling of utter satisfaction. We have worked for 20 years to get this moment, to see this data. And we -- people said it couldn't be done; it was just impossible. So, it was very satisfying to see the data that says, yes, we're getting the answers that we have -- we have worked so hard over all these years.
SPENCER MICHELS: Borucki and his colleagues can't see Kepler-22b. It's too small and too far away. The fastest modern rocket ship would take 24 million years to get there.
Scientists also know little about the atmosphere or what the planet is made of. It could be more like gassy Neptune than Earth. But they can interpret data.
What can you do with that knowledge?
WILLIAM BORUCKI: What we're trying to do with this knowledge is, we're building a picture, and the picture is, how many stars in all the galaxy have planets something like the Earth, where life could be possible?
If the answer is many, then there's probably a lot of life in our galaxy. And the next instruments that get built to look at the atmospheres will look just at the close-by stars, because most of them will have planets, so you won't have to look very far.
SPENCER MICHELS: Scientists are taking the discovery of a potentially habitable planet seriously, even if it is 600 light years away. At SETI, the Search for Extraterrestrial Intelligence, they are planning on following up the NASA discoveries.
SETI operates a bank of 42 small radio telescopes from a site near a fine fishing stream in Northern California. Its director for research, Jill Tarter, says those telescopes will now focus in on Kepler-22b.
JILL TARTER, Search for Extraterrestrial Intelligence: Well, that's certainly one place that we want to look, because we want to ask the question and perhaps find the answer, does anybody live there? And this particular Kepler-22b is the smallest, most Earthlike planet of those that we know to be in the habitable zone. So it's a clear winner in terms of us pointing our telescopes there.
SPENCER MICHELS: How do they attempt this?
JILL TARTER: We're looking for radio signals that appear to be engineered, that don't look natural, but look like someone generated them in order to attract our attention.
SPENCER MICHELS: You're looking for life then, intelligent life?
JILL TARTER: Well, we're looking for the technologies, right. And if we find the signals that are engineered, then we will infer that, at least at some point, there were technologists.
SPENCER MICHELS: And does NASA's Borucki think there may be life out there?
WILLIAM BORUCKI: I think there's a very high possibility of life, but I'm speculating. Up to now, what I have been telling you are facts. These are the measurements we have made. And it is the difference between science and speculation.
SPENCER MICHELS: Meanwhile, the search for more planets in the habitable zone goes on, and so does the search for ways to figure out what's going on in places scientists can't even see.