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(Becky Lowder)

Bill Borucki's Planet Search

Finding another Earth may be easier than the Kepler project's long quest for funding.

He was in the right place. In the 1970s Ames hosted a session on space colonization, and it also was the home of NASA’s Search for Extraterrestrial Intelligence. Borucki got to know many of SETI’s legendary figures, including Carl Sagan and Jill Tarter.

In the summer of 1982, Borucki looked in on an Ames conference on extrasolar planets, a far-out topic at the time. Transit photometry was mentioned only in passing because detectors of the day simply couldn’t measure stellar variability to the degree necessary. “We needed precision of one or two parts in a hundred thousand, and no one knew how to get there,” he recalls.

The idea of transit photometry wasn’t new. Astronomer Frank Rosenblatt speculated in a 1971 paper that the method could prove a valuable tool, but he died shortly thereafter.

Borucki picked up the thread and became increasingly intrigued—some would say infatuated—with the possibilities. He published a couple of papers on the subject, and in 1984, he somehow persuaded the director of Ames to fork over enough money from his discretionary purse to fund a small conference on the subject.

Roughly 20 astronomers attended the meeting, held in San Diego, and decided that it was theoretically possible to build such detectors. Scientists at the federal National Bureau of Standards suggested silicon diodes as quantum-perfect detectors—devices that would spit out a single electron for every photon of light absorbed. For three years Ames’ director used his discretionary fund to pay for Borucki’s development of silicon diode detectors, but Ames managers questioned how well the detectors would operate in space and remained skeptical.

In the late 1980s, Borucki’s team began to look at charge-coupled devices—technology more familiar to the astronomical community. Unlike silicon diodes, which can monitor only one star at a time, CCDs are array detectors that can survey thousands of stars simultaneously and are ideal for digital data gathering. Borucki had tested CCDs years before and had been disappointed with their degree of precision, but his team determined that newer CCDs were capable of the precision necessary to detect minuscule brightness changes. Though they’d never be as precise as silicon diodes, Borucki chose to go with CCDs for credibility.

“I hate CCDs,” he says, chuckling but serious. “The only reason I chose them was because I knew I had to convince the community that we could do the job. It was easier to convince them with CCDs than it was with silicon diodes.” His spacecraft would eventually require dozens—the most recent design calls for 42, compared to the Hubble Space Telescope’s four.

Here to There
In early 1993, Ames called for a review of Borucki’s work. Just as space-qualified CCDs were becoming commercially available, Borucki gave an eight-hour presentation that convinced Ames of his project’s feasibility.

New data from NASA’s Solar Max mission lent a supporting hand. “Solar variability was coming out to about 10 parts per million. At the time scale of a transit, solar variability is much smaller than a transit,” says Dave Koch, Kepler’s deputy principal investigator and Borucki’s right-hand man. “The [review] committee said ‘Yes, this can now be done. It’s not just a cute idea, it really is a practical idea.’ ”

From then on, the center quietly provided a steady stream of money for the project. Ames officials backed the high-risk research for its own sake, but they were also aware of the interferometer work being done by their NASA rivals at the Jet Propulsion Laboratory in Pasadena, and entering the planet race appealed to their competitive instincts.

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