At home in the heavens
Astronomers are closing in on other solar systems that resemble our own. They could harbor Earth-like planets
It took years of observing before Marcy, Butler, and their colleagues were ready to announce their Jupiter, because their technique depends on watching a star get pulled to and fro through a planet's full orbit. A Jupiter takes 12 years or more. Yet this one, 41 light-years away, is still an imperfect match to our own. The same star has two other giant planets, one of them a Jupiter-size body in an orbit so small that it completes a revolution every 14.6 days. It probably got there by migrating inward from the planetary system's outer reaches soon after it formed. That could mean no Earths, says Carnegie theorist Alan Boss. "Bodies that were going to form terrestrial planets undoubtedly got kicked out of the way by this big guy that came muscling through." But other Jupiters, without heavyweight companions, may be lurking among the hundreds of other stars that Marcy, Butler, and others have been watching. A couple more years of observations may tease them out.
Even before then, other astronomers including Jayawardhana may short-circuit the search by taking a picture of an alien Jupiter. A giant planet near a young star--less than 100 million years old, a baby compared with our 4.6 billion-year-old sun--would still be hot from its formation, glowing with infrared light. It could be just bright enough to register in a giant telescope like the Keck, equipped with "adaptive optics" technology that detects and cancels out the atmosphere's blurring. The discovery would signal a solar system in the making, and light from the planet might show the fingerprints of the same gases seen in our own Jupiter, including water, methane, and ammonia.
On the same February night while Marcy and Butler were at the controls of Keck I, Jayawardhana, David Charbonneau of the California Institute of Technology, and Brigitte Koenig, a Ph.D. student at the Max Planck Institute in Germany, were in the adjoining control room, observing on Keck II. They were working through a list of young, sunlike stars within 100 light-years or so of Earth. One star on the agenda was especially tantalizing, because earlier observations on the Hubble Space Telescope had revealed a faint point of light right next door. It could be a planet. But it could also be a star much farther away that happened to be lined up just right to fool astronomers. One way to tell is to take a second look to see if the spot wanders across the sky in tandem with its star, as a planet would be expected to do.
One by one, the planet hunters inspected their stars. Each time the telescope locked on to a new target, there was a pause while the adaptive optics system got to work. It bounced the starlight off a flexible mirror that bends, twists, and quivers hundreds of times a second to cancel out atmospheric turbulence. After each star flared into view on a monitor, the astronomers tapped commands to maneuver a tiny light shield inside the detector until it masked the star, making it easier to see any faint neighbor.
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