Bill Borucki's Planet Search
Finding another Earth may be easier than the Kepler project's long quest for funding.
- By Andrew Lawler
- Air & Space magazine, May 2003
It should have been a moment of triumph: The maverick prophet finally welcomed into the high temple. After 20 years of dogged and often lonely effort bordering on obsession, Bill Borucki had won approval from NASA to build the first spacecraft designed to find Earth-size planets beyond our solar system. If successful, his mission, named for Johannes Kepler, the astronomer who calculated laws of planetary motion, could rewrite our understanding of solar system formation and single out targets in the search for extraterrestrial civilizations.
But in January 2002, just weeks after the mission’s approval, Borucki’s legendary patience was tested by a meeting held with officials in a windowless room at NASA’s Washington, D.C. headquarters. Agency managers first offered congratulations, only to sheepishly explain they were short on cash and had to delay the project’s launch by a year, to 2007. What’s more, the team would have to turn control of the project over to a rival NASA center. When Borucki informed his colleagues—a close-knit mix of seasoned space veterans and eager postdocs—they were astonished, then furious. “People turned colors,” Borucki recalls with a smile.
After living in the wilderness for so long, Borucki was not about to let small matters such as money or management derail his project. While others on his team continued to rant and fume, Borucki quietly returned to his office at NASA’s Ames Research Center, south of San Francisco, and set about doing what the agency hierarchy requested.
“All I care about is the science,” he says one evening over Chinese food. Coming from most scientists, the statement would sound naive or simply platitudinous, but Borucki leans his spare frame forward, and this time he doesn’t smile. “And when I go home tonight,” he says, “I will work.”
The search for extrasolar planets is one of the most spirited pursuits in modern astronomy, with potential Nobel Prizes driving physicists as forcefully as innate curiosity. Since a Swiss team located a giant planet in the constellation Pegasus in 1995, researchers have racked up around 100 planetary systems and many more candidates. The race now is to find Earth-size planets; the holy grail is to find one in the habitable zone, where temperatures would allow liquid water—and therefore possibly life—to exist.
The standard method for planet searching, astrometry, involves looking for a regular wobble in the parent star—a sign of its brood’s gravitational tug—but the worlds discovered by this technique are typically larger than Jupiter and often orbit as close to their stars as Mercury does to the sun. Though important for the impact they’ve had on solar system formation theories, the planets are hardly Earth-like. With current technology, astrometry is also limited; at best it can spot terrestrial planets only around the nearest stars. And enormous practical challenges involving precision flying and mirror technology still have to be solved before interferometry and coronagraphy, conventional ground-based approaches, will work from a platform in space.
To find smaller planets at greater distances, other methods are needed; it’s here that Borucki is cutting a new path. His small and relatively simple spacecraft, Kepler, will employ a revolutionary technique called transit photometry, which precisely counts photons from a star’s light to detect periodic dips. Kepler will fix its eye on 100,000 stars in the constellation Cygnus, and during a four-year mission around our sun it will stare relentlessly at those stars for dimming, which could mean planets are passing over the faces of—transiting—their home suns. Three dips of the same duration and degree and at equal intervals would confirm an orbiting entity.
Cygnus, lying 55 degrees above the solar system’s ecliptic plane, is a particularly good target; it’s home to a dense star field and can’t be obscured by asteroids or sunshine. Borucki’s team will study around 135,000 of the constellation’s dwarfs—those similar to our sun—and after a year weed out roughly 25 percent that are too variable for transit spotting. Before budget issues and hardware reliability come into play, Kepler will have the opportunity to see up to four transits by planets in one-year orbits and up to three by those in 1.9-year orbits.