Geoffrey Marcy

QUESTION: Talk about your work in detecting new planets.

MARCY: The Doppler technique involves watching a star to see how it is gravitationally pulled by its attendant planets. We are lucky that with this Doppler technique that we have perfected, Paul Butler and I, we can detect Jupiters and Saturns orbiting any of the stars within about a hundred light years of our solar system. This is a wonderful opportunity, the first time in the history of humanity, that we've been able to detect any planets outside our solar system. We are now able to detect not just the big boys like Jupiter but smaller ones like Saturn and maybe ones like Neptune and Uranus.

When I was a kid, I remember learning that the earth goes around the sun, all nine planets go around the sun. Actually, that's not quite right. The planets are tied to the sun gravitationally, and just like the Earth is gravitationally attracted to the sun, the sun, in turn, is gravitationally attracted to the Earth. So as the Earth goes around the sun, our sun, in effect, goes around the Earth a little bit. That is, it is yanked around by the Earth, but the Earth has such a low mass that the Earth doesn't really yank the sun around very much at all. Jupiter, on the other hand, really does yank the sun around. And so that's what we try to measure.

Our goal is basically to sieve our all of the big planets in our galactic neighborhood, within 100 or 200 light years, and that's what we're endeavoring to do here at the Keck telescope. We have a survey of about 400 stars — in fact, we just augmented it to 430 or so — and these are all of the solar light stars, some a little bigger, some a little smaller than our sun, but all the solar light stars in our galactic neighborhood around which we hope to find all of the Jupiters and all of the Saturns that exist.

QUESTION: Can we currently detect Earth-like planets using the Doppler technique?

MARCY: The Doppler technique, and indeed any of the existing techniques are currently not capable of detecting earth-like planets. Earths are very little, and they don't reflect very much light, and they aren't massive enough to push around their star gravitationally. For those reasons, earth-like planets are extraordinarily difficult to detect.

QUESTION: So what you're observing now are the stars themselves?

MARCY: The irony is that all we're observing right now are stars. We watch the star night after night, month after month. We come back. We observe the same set of stars over again, and what we're looking for is to see whether the stars wobble. If the star does wobble, it must be doing so for a reason. Stars should not be moving on their own accord. Therefore, it must be doing so because a planet is pulling on it as the planet goes around. And that's the whole game.

QUESTION: Are there other astronomical influences that cause stars to wobble?

MARCY: There are some buggaboos in this game—the most scary thing to us is that stars might pulsate, breathe in and out. Imagine a star breathing in and out, what you would see is the star coming at you and then away from you, and then at you and then away from you. That would give the same wobbly effect that we would detect here at the telescope. Therefore, it could mimic the existence of a planet.

It turns out, luckily, that sun-like stars, and our own sun, do not pulsate. They don't oscillate, they don't ring like bells. Our sun is a nice steady sphere. If it were not for that, our planet search wouldn't work at all.

QUESTION: Are you looking for other planets around stars that exhibited the presence of one planet already?

MARCY: One of the most exciting endeavor that Paul and I are engaged in that should yield fruit, hopefully in the next year or two, is the detection of additional planets to stars for which we've already detected one planet. This would be very exciting because finding just one planet around a star seems not just lonely in the emotional sense, but it renders the system architecturally different from our own solar system, which, of course, has nine planets. So the question is; Are there other planetary systems out there that have multiple planets? Until we find one with multiple planets we have not actually found a kin of our own solar system.

QUESTION: Is our solar system a common, garden-variety solar system?

MARCY: Our solar system has a beautiful architecture. We have the Earth at just the right distance so that water is in liquid form which renders it possible to have not just fish and drinking water, but the petri dish in which life itself formed.

The architecture is beautiful, too, because we have Jupiter out at five Earth-sun distances. Jupiter is sort of our great protector, you see. Jupiter is this scouring device that scatters the asteroids and the comets from our solar system over the billions of years, rendering the Earth a much more tranquil environment than it otherwise would be. Wouldn't it be awful if every few years another comet ran into the Earth and smashed into the Yucatan Peninsula which, is of course, the way the dinosaurs met their demise?

Instead Jupiter has more or less gravitationally scoured our solar system, rendering it safe, tranquil for the evolution of life. So we're lucky that the architecture of our solar system is just as it is. And the sad truth is we don't yet know whether there are other planetary systems that are quite a bit like our own, with the Jupiter and the Earth in just the right positions