Inside the planet hunter's lair
Geoff Marcy, astronomy’s Indiana Jones, had 10 days, one telescope, and a universe of planets to discover.
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Astronomers have known, theoretically, how to find extrasolar planets since the early 1900s: Measure how much a planet moves its star. Marcy explains that every planet has a small gravitational pull on the star it orbits, which causes the star to move, or “wobble,” a tiny bit.
Marcy illustrates this effect by asking me to grab his outstretched hand. I am sitting in a swivel chair, and Marcy, holding my hand firmly, runs around me in a circle. He is the planet; I am the star. I, of course, do not rotate on a perfect axis, but am pulled in a messy circle that leaves the rug beneath my chair a rumpled mess.
The demonstration is an exaggeration, but it makes the point. For a star, that tiny wobble causes small changes in the lightwaves it emits. Those changes – called Doppler shifts – are measurable now. But they weren’t in 1983, which is why Marcy had the field pretty much to himself.
“The technology then was like using a cop’s radar detector to measure the speed of a snail,” he says. “It just couldn’t be done.”
So for 12 years, Marcy and a former student, Paul Butler, labored day and night to refine the technique of measuring stars’ lightwaves. They applied related solutions from other research, and honed their computer analysis until they were able to detect movement as slow as three meters per second. That’s about the speed of a medium-paced jogger.
In 1995, they hit the jackpot, detecting not one, but two planets. Although Marcy wasn’t the first – a Swiss team had found a planet about two months earlier – his discovery caused a scientific stir, a media firestorm, and something of a stampede into the field. These discoveries, says Boss, have made the pioneer planet hunters excellent candidates for a Nobel Prize.
A total of some 300 planets have been detected by astronomers so far. But all of them are considerably heftier than Earth. A few recent finds have been a mere five times the bulk, but most are equivalent to Saturn or Jupiter – about 100 to 300 times the mass of our beloved blue home. Which means they’re probably gaseous, or have little atmosphere and less water, and are therefore very unlikely to support life.
So the quest goes on.
During this stint with the Keck, Marcy has targeted about 300 stars, all of which he suspects have one or more orbiting planets. With the help of Howard and a telescope operator in Hawaii, Marcy collects the stars’ light and directs it through a state-of-the-art spectrometer that breaks the light down into 100,000 shades of the rainbow spectrum. Those breakdowns form “snapshots,” and by comparing many snapshots from each star, Marcy measures the Doppler shifts to determine if the stars are wobbling.
After days of crunching data using algorithms that Marcy and his team devised themselves, Marcy and Howard begin writing up their findings: This time, they’ve found two “new” planets that are nine and 10 times the size of Earth.
Marcy is also at work on technology to find ever-smaller planets. He expects astronomers to discover something the size of Earth in the next three years.
All of which raises the question: What then? At this, he lights up and outlines two options. The first is to look directly at the planet with a huge space-borne telescope. But this would be years away, as the telescope is not yet funded, much less designed or launched.
A second option is the old “phone home” technique. Marcy would seek to contact the planet directly by beaming anything we’ve got at them – X-ray, radio, and lightwaves – and “ask them to fax us a picture of their planet.”
It’s a typical Marcy-an response – funny and inquisitive. But the message is serious, and a bit like the caution on every side-view mirror – Warning: Extraterrestrial life is closer than it appears.