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Is There Another Earth Out There?

Leading planet-finder predicts discovery of another 'Earth' within decade

April 7, 2003
Geoff Marcy
Blue Line
Geoff Marcy
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Geoff Marcy is professor of astronomy at the University of California, Berkeley, and a Principal Investigator with NASA's Space Interferometry Mission (SIM). Along with Paul Butler of the Carnegie Institute in Washington, Marcy co-leads a team that has discovered more than 70 planets outside the solar system. Marcy was interviewed during a recent SIM science meeting in Pasadena, California.

PlanetQuest: Humans have been speculating on the existence of worlds around other Suns for thousands of years, but there was no evidence until that first discovery was made in 1995. Since then, more than 100 extrasolar planets have been discovered. Why is all this happening now?

Marcy: The discovery of planets around other stars is extraordinarily difficult. The problem, in a nutshell, is that a planet is about 1 billion times fainter than its host star, so the planets get lost in the glare of the host star. The reason we're finding planets now, by this doppler technique, is that now we have big telescopes, fast computers and most importantly, exquisite optics.

PQ: So far, all of the planets discovered are gas giants. How long will we have to wait for the discovery of Earth-size planets?

Marcy: NASA is launching two missions within a decade, both explicitly to detect Earth-like planets. The Space Interferometry Mission (SIM) and Kepler will determine whether there are Earths out there and how often Earth-like planets occur. What fraction of the twinkling stars you see out there are going to have Earths? We're going to have the answer in 10 years or less.

With SIM, we're going to survey about 200 nearby stars. The interesting problem we face is that we don't know how many planets it's going to find. It might turn out that every star has an Earth or a Venus or a Mercury or a Mars -- a smallish planet heretofore undetectable. That's the great part about SIM -- we don't know the answer ahead of time. We don't know if we'll find three planets or hundreds. We have to do the experiment to find out.

PQ: Why are Earth-sized planets considered the "holy grail" in planet-finding?

Marcy: What we're trying to do with SIM is to find planets that have a rocky, wet surface. It is that liquid water that provides the solvent for biochemistry -- the chemistry of life -- to flourish. So we're looking desperately for planets with a surface that can hold those pools of biochemistry that we think would eventually lead to complex life.

PQ: Why should the general public care about this quest?

Marcy: The discovery of planets around other stars will never change the price of any stock on the U.S. stock exchange. NASDAQ isn't going to budge when we find a new planet. But I think there is great value in finding out if there are other planets out there, and I think the main reason is simply because we want to know if we're alone in the Milky Way galaxy with its 200 billion stars.

When you look up at the night sky at those twinkling lights, you wonder: Are any of those suns like our own Sun? Is our solar system unique? And we're getting answers. There are other planetary systems, and the chances for life on some of those planets, if conditions are right, are very high right now.

Comparison of our own solar system with a system discovered by Marcy's team around the star 55 Cancri in June 2002
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Comparison of our own solar system with a system discovered by Marcy's team around the star 55 Cancri in June 2002
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PQ: How did you first get interested in astronomy?

Marcy: When I was 14 years old, my parents bought me an old, used telescope. They weren't sure if I would like it, but I put that telescope up on the roof of our house, and I used to look up at Saturn at night. I was stunned that you could actually see the rings of Saturn. I was captivated. From that moment on, I knew I wanted to be an astronomer.

PQ: Were there any teachers who had a strong influence on you?

Marcy: I had a fantastic teacher when I was in sixth grade. I was told to ask questions, to not accept, necessarily, what the establishment told me. I've asked questions ever since, and it's been very helpful.

PQ: Have you ever had a "eureka" moment?

Marcy: I'll never forget the morning of December 30, 1995. I was at home, preparing for New Year's Eve, and my collaborator, Paul Butler, called me up and said just three words -- "Geoff, come here." He was already at the office. It was a Saturday morning. I drove immediately to Berkeley, and there on the computer screen was a plot showing the wobble of (the star) 70 Virginis. We had been looking for planets around stars for eleven years without a single success, and there on the computer screen was the first planet we had ever discovered. It was a fantastic moment.

PQ: How did you feel?

Marcy: I was scared and elated, if you can imagine it: terror at the prospect that we might be wrong, and the excitement of knowing we had found our first planet. We knew there was only one thing to do at that point: take more data, to make sure we were right.

PQ: Do you have any words of advice for someone considering a career in science?

Marcy: If you're considering a career in astronomy or science, there's a very clear path. First, when you're in high school, take lots of science classes, lots of math classes. The second piece of advice -- go with your heart. Find out what you really get a kick out of, and go with that. Be in touch with what you're really excited about.

PQ: What do you like to do in your spare time?

Marcy: I play two hours of tennis every day, sometimes twice a day. If I had my life to live over again, I'd be a professional tennis player.

PQ: What do you find most rewarding about your work?

Marcy: There are two things I like about being a scientist and doing research. One, is that occasionally I come into the office and work, and by the end of the day, my colleagues and I come up with a new discovery, perhaps a new planet, that no one has ever known about. The discovery of something that has never been known in the history of humanity is a wonderful experience.

The other thing I like about doing research is being with my collaborators. They are my friends, almost like family. From the day-to-day standpoint, it's just working with others, working with my collaborators, that makes science enjoyable.

NASA's PlanetQuest