Astronomer Geoff Marcy hunts the sky for planets that could sustain alien life. For many years, people thought he might be crazy. When I would tell other scientists that I was hunting for planets around other stars, they would look down at their shoes, embarrassed for me. You might as well be looking for fairies or for alien civilizations in the pyramids. Its hard to believe, but until recently, there was no proof that other planets exist outside our solar system. No telescope on Earth nor satellite in space was powerful enough to spot anything smaller than stars. The reason is simple. Planets dont shine. They dont reflect very much light from their host star. Theyre dark specks of dust, if you will, floating around the universe, and people understood you probably could never detect them. Marcy refused to accept that. Risking professional ridicule, he was determined to find a way to spot far- off worlds. Eventually, he found one. It turns out that while planets may hide from our eyes, they cant hide from the stars they orbit, what astronomers call their host stars. Finding planets is actually very simple. We watch the host star, represented by my head, as the planet, represented by the tennis ball, orbits that star and pulls gravitationally on the star. As it does so, the star, my head, wobbles around, being pulled by the planet, and back on Earth, our telescopes can watch to see the wobble of the host star as the planet goes around it. Even if you dont see the planet, you can see the star wobble around. Its difficult to see it directly, but we use the Doppler shift of the stars light. As the star comes at you, the light waves emitted toward the Earth get compressed, and as the star goes away from you, the light waves get stretched out in their travels to the Earth. And so you can see the light waves compressing and stretching and compressing and stretching, which, to our human eyes, means the color changes. We see the colors change from bluer to redder to bluer to redder, and we can measure that at the back end of a telescope. This effect is well-known, the Doppler effect, with sound. You can hear the pitch of a train whistle change as the train goes by you. Even with your eyes closed, you can tell whether the train is coming or going, and so it is with light waves from a star. You can tell whether the star is coming or going from the changing pitch of the light waves. For nearly a decade, the Doppler shift method of planet hunting was an experiment with no positive results. Marcy still couldnt prove that planets exist outside our solar system. But he slowly won a few astronomers over to his way of thinking. He was no longer the sole Detective on the investigation. In 1995, his patience was rewarded. A group of Swiss astronomers had their eyes on a bright object in the Pegasus constellation called 51 Pegasi b. The Swiss suspected they had found what everyone was looking for -- a very large planet, the first one seen outside of our solar system. But they needed confirmation. Luckily, my student, Paul Butler, and I had telescope time assigned to us just a week later on the Lick Observatory four consecutive nights, and as luck would have it, the supposed orbital period of this planet around 51 peg was four days. Perfect match. We went to the telescope. All four nights were clear. We measured the Doppler shift of 51 peg, and we drove off the mountain that the Swiss had been correct. It was a marvelous moment, and the world was introduced at that time, in mid October 95, to the notion that our solar system was not alone. The discovery of 51 Pegasi b changed the entire game. The Doppler shift method of planet detection was proven successful, and soon Marcy and his colleagues found more and more alien worlds. They have slowly confirmed nearly 450. There are likely billions more. But Marcys goal hasnt changed. He wants to find worlds like Earth that orbit in the habitable zones around their host stars, the comfortable place where its not too hot and not too cold Worlds that could possibly support some form of life. Planets in this habitable zone may have a key ingredient for life as we know it. If you took any organism on Earth, and you took out the water, youd end up with some powdered amino acids, proteins, nucleic acids, a few fats -- you know, these sorts of things. But they dont work in a powdered form. You dont get the chemistry that would make life. So you need some kind of liquid, some kind of solvent to dissolve all these chemicals in. What all life on Earth uses as its solvent is water, liquid water, and so that is what we look for as a first step to looking for life elsewhere -- the presence of liquid water. But finding habitable planets isnt easy. Planets like Earth are small, and their host stars shine billions of times brighter, so theyre hard to see. Looking for solar wobbles isnt easy, either. Now imagine a smaller planet. My head still represents the host star, and as this small planet orbits the star, it has so little mass, it hardly yanks gravitationally on my head, the host star, at all, making the detection of small Earth-sized planets very difficult. Marcy has gone from crazy outsider to the peak of his profession without changing his position. He doesnt back down in the face of a challenge. He plans to keep combing the cosmos a section at a time, looking for stars similar to our sun and enjoying the fruits of our ever-evolving technology. Here we are, about to answer a question that the ancient Greeks asked and humans undoubtedly asked even before then. Its a treasure of a moment in human history that we suddenly have at our fingertips the telescopes, the computers, the light detectors, and the knowledge to answer a philosophical question that humans have been asking since antiquity. The answer to that question Are We Alone? May come sooner than we think. Because for the first time ever, we have an undercover Detective not tied to the Earth, but floating in the heavens A special Agent in space specifically designed to track down
Posted on: Sun, 21 Dec 2014 19:30:29 +0000
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