The origin of the term "eureka" traces back to an unexpected gift and a bath tub.
Derived from the Greek heureka [ "I have found (it)"], traditionally the story attributes this exclamation to antiquity's greatest mathematician, Archimedes, when he realized during bathing that the volume of an irregular solid could be calculated by measuring the water displaced when it was immersed. Many scientists have since immersed themselves in such seemingly unsolvable problems, but few can rival the challenges of finding an entirely new world.
One of the most remarkable "eurekas" of our time is the ability of planet hunters to infer the existence of entirely new worlds -- often only with the help of a tiny wiggle in the star's light, motion, or color.
For instance, if the light constancy of a star varies, it may be undergoing a dim eclipse by a planet. This search method is called the transit method.
If the star's light seems to change color from red to blue and back again, the star may have an orbital companion. This "Doppler shift" indicates a star being tugged back-and-forth by an orbiting planet's gravity. This search method has been the most productive so far, finding over one hundred planets.
If a star shows both motion and light change, it may mean the starlight is bent or focused by the gravity of a companion (thereby fulfilling the promises of Einstein's theory of general relativity). This "gravitational microlensing" search method is relatively new, and offers yet another tool for planet hunters.
One of today's most prolific planet finders is Geoff Marcy. In a recent interview, he shared his own "eureka" moment that occurred on the morning of December 30, 1995. He described eleven years of looking for the signs of a new planet, only to be summoned by a colleague's understated: "Geoff, come here."
Marcy's moment is reminiscent of the famous "eureka" that led to the first telephone, when Alexander Graham Bell called his colleague by saying, "Watson, come here." Bell needed help because he had spilled acid on himself. The acid catalyzed a battery that communicated his voice across a wire to the next room.
As astronomers around the world continue to scan the sky for planets, the rallying cry may as well be, "Planets, come here."
Interview with planet hunter, Geoff Marcy
Question (Q): 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.
Q: So far, all of the planets discovered are gas giants. How long will we have to wait for the discovery of Earth-size planets?
|Geoff Marcy, a planet hunter from UC Berkeley
Image Credit: astron.berkeley.edu
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.
Q: 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.
Q: 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.
Q: How did you first get interested in astronomy?
|The star, Lalande 21185, a dim red dwarf, may have as many as three Jupiter-class planets -- including innermost planetary candidate "b" depicted with rings and two moons
Credit: John Whatmough
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.
Q: 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.
Q: 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.
Q: 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.
Q: 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.
Q: 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.
Q: 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.
During the next 15 years, American and European scientists hope to launch more than half a dozen missions to search our corner of the Milky Way galaxy for terrestrial planets.
To search for Earth-like planets around stars beyond our solar system, the space-borne telescope Kepler Mission is scheduled for launch in 2006. Kepler will simultaneously observe 100,000 stars in our galactic neighborhood, looking for Earth-sized or larger planets within the "habitable zone" around each star - the not-too-hot, not-too-cold zone where liquid water could exist on a planet.
|The gravitational pull of an unseen planet causes a star to wobble. As the star moves toward an observer, the wavelength of the star's light is squeezed and becomes more blue. As the star moves away from the observer, the wavelength is stretched and the light becomes more red.
One NASA estimate says Kepler should discover 50 terrestrial planets if most of those found are about Earth's size, 185 planets if most are 30 percent larger than Earth, and 640 if most are 2.2 times Earth's size. In addition, Kepler is expected to find almost 900 giant planets close to their stars and about 30 giants orbiting at Jupiter-like distances from their parent stars.
After Kepler, NASA is considering a 2009 launch for the Space Interferometry Mission (SIM). SIM's primary mission will be to measure distances to stars with 100 times greater precision than currently is possible. This will improve estimates of the size of the universe, and help determine the true brightness of stars, allowing us to learn more about their chemical compositions and evolutions. SIM also will look for Earth-sized planets in the habitable zones around some 200 stars.
SIM will be an interferometer, which means it will combine interacting light waves from three telescopes. This interaction, called interference, makes the individual telescopes act as though they were a single, larger telescope with greater light-gathering ability.
Future missions will search for many more planets. ESA's Herschel mission, for instance, will take detailed pictures of stars that might harbor dusty remnants of entire solar systems. As these images become available, astronomers will be able to predict the sizes and orbits of giant planets within the distant solar system.
Geoff Marcy is professor of astronomy at the University of California, Berkeley, and a Principal Investigator with NASA's Space Interferometry Mission. 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 by JPL during a recent SIM science meeting in Pasadena, California.