TOPICS > Science

Astronomers Spy New Planet in Distant Solar System

November 7, 2007 at 6:45 PM EDT

JIM LEHRER: Finally tonight, something new in the distance. Jeffrey Brown has our Science Unit update.

JEFFREY BROWN: The distance is actually 41 light years from Earth, where scientists think a solar system exists that may well be similar to our own. At the center of the system is a star called 55 Cancri, which can be seen from Earth in the night sky.

Now scientists have announced the discovery of a fifth planet orbiting that star. The planet is about 45 times the mass of Earth.

Here to tell us about it is Geoff Marcy, a professor of astronomy at the University of California, Berkeley. He was one of the scientists on the team that discovered the new planet.

So, Geoff Marcy, what’s the significance of finding a fifth planet? What does it tell us about the solar system?

GEOFF MARCY, University of California, Berkeley: Well, what’s lovely, of course, is that our own sun harbors eight planets — major ones, anyway — and now we’ve finally found a star, which, by the way, is very similar to our sun — the same mass, almost the same age, nearly the same chemical composition as our sun — and this star harbors five planets.

So we’re beginning to see full families of planets orbiting other stars, giving us a sense that our own solar system is not unusual, that, in fact, there are many such examples of planetary systems elsewhere in our Milky Way Galaxy.

Features of the new planet

JEFFREY BROWN: And how similar are these planets -- the new one, for example -- how similar to Earth or planets in our own solar system?

GEOFF MARCY: Well, the new planet we just found, Debra Fischer, Paul Butler, Steve Vogt, my team found, is 45 times the mass of the Earth, much bigger than our Earth. But what's really interesting is that the full architecture of this planetary system is quite reminiscent of the structure of our own solar system.

There's the star. Far away from it is a large, Jupiter-like planet, four times the mass of Jupiter, but in a Jupiter-like orbit, same distance, circular. And then inward of that outer Jupiter are four smaller planets. And this, of course, is quite reminiscent of our own solar system, with its Jupiter and four terrestrial planets orbiting closer in.

So for the first time we're beginning to see other solar systems, if you will, that remind us of home.

JEFFREY BROWN: All right, so the obvious question is whether being like our solar system suggests the capability of having life like our solar system. What do we know now? And what are you looking for to answer that kind of question?

GEOFF MARCY: Well, the real $60 million question is whether or not there are Earth-like planets elsewhere in the universe. And, frankly, we haven't found any yet. It's not for lack of trying. We don't quite have the technology yet to find other Earth-like planets.

In 55 Cancri, with its existing five planets, all of which are bigger than the corresponding planets in our solar system, there's a large gap between planet four and planet five. And in that gap could well be rocky, Earth-like planets that our current technology isn't quite capable of detecting.

Possible life on the new planet

JEFFREY BROWN: The new planet, though, that you found, I understand it's in something you call a "habitable zone," close enough to its sun, but not too far away, which suggests it's in that area, at least, where life might be possible?

GEOFF MARCY: That's right. Planets that orbit close to their host stars are, of course, blowtorched to high temperatures. Planets that are far from their star are too cold. The water, if any, would be frozen into ice.

And there's a zone in between that has a temperature, as Goldilocks said, just right for life, and that is what we call the habitable zone. Our Earth resides smack in the middle of the habitable zone around our sun.

JEFFREY BROWN: Now, you mentioned the technology and the limits that you have so far. I said in the introduction that the star at the center of this can be seen, these planets cannot be seen as we think of seeing usually. You use this wonderfully titled method called the wobble method. Explain to us how you see these planets.

GEOFF MARCY: Well, it's remarkable. You know, even with the Hubble Space Telescope pointed at a nearby star, you can't see the reflected light from the planet due to the glare of the host star.

So we use a trick. We actually watch the star itself. And a star will wobble in space if it's being yanked on gravitationally by any planets that happen to orbit it. So we can't see the planets, but we do see the star wobble in space. We watch the star for months and years, and thereby deduce the masses and the orbits of the planets.

Expanding space understanding

JEFFREY BROWN: Now, how do you extrapolate, finally -- and you said a little earlier that you can use this new finding and say it suggests that there are many other solar systems out there in the universe. How do you extrapolate from this to say that this shows that we're really not all that unusual after all?

GEOFF MARCY: Well, we've only been monitoring stars for about a decade. And in particular, at the Lick Observatory, we had 50 stars that all would have been amenable to the same sort of discovery that we've made around 55 Cancri, a full family of planets. And out of those 50 stars, one of them, indeed, does have five planets. Several others have two or three planets.

And so what we're seeing is that, out of a few dozen stars we've been monitoring, quite a large number of them have a family of planets. And that tells us that, in our Milky Way Galaxy, with its 200 billion stars, there are billions and billions of planetary systems just within our Milky Way Galaxy alone.

JEFFREY BROWN: And so, briefly, what happens next? What do you look for next?

GEOFF MARCY: Well, the exciting thing is that NASA is planning several missions specifically to find Earth-like habitable planets. That's the Holy Grail. We're still looking for that first Earth twin.

There's the Kepler Mission, which we're planning to fly in about a year-and-a-half, specifically designed to find Earth-like planets in this habitable zone. And then NASA also wants to build an interferometer, an interferometry mission that would find Earths. And then the grandest of all, the Earth-like seekers, the terrestrial planet finder, a mission NASA would like to build to take the first pictures of a pale blue dot going around a yellow, sun-like star.

And I think it would be marvelous someday to open up the newspaper and see, indeed, that picture the next day the pale blue dot will have orbited around, and we'll know that there are Earth twins out there.

JEFFREY BROWN: OK, that would be marvelous, indeed. Geoff Marcy at UC Berkeley, thank you very much.

GEOFF MARCY: Thank you.