Nailing the Numbers
With Kepler’s selection, Borucki’s biggest victory may have been on behalf of Ames in its sibling rivalry. Up to that point, says Kent Cullers, who is in charge of R&D at the now-private SETI, “JPL has had the lion’s share of the R&D funding” for finding Earth-like planets.
JPL managers, once critical of the project, now sing Kepler’s praises. “Kepler will do a great job nailing down the numbers” of terrestrial planets, predicts Charles Beichman, chief scientist for NASA’s Terrestrial Planet Finder program. Its findings may help determine the TPF mission’s design. “We’ve pushed Kepler aggressively in the last four or five years,” he adds, though he admits that in “the mists of time,” questions were raised about Kepler’s efficacy. “Now it is very solid and credible,” Beichman says.
Beichman and others are nevertheless quick to point out Kepler’s limitations; imaging stars mostly at great distances using photometry, Kepler can find evidence of terrestrial worlds but can’t provide more specific characteristics. So while astronomers will learn much about the distribution of such planets, it will be up to later missions to pinpoint what kinds of atmospheres and surfaces such worlds might have—and whether life exists on them.
NASA will seek answers to these questions with its Origins missions, which will include Hubble’s successor, the Next Generation Space Telescope; the Space Interferometry Mission, which will search among wobbling stars for planets; and the still-far-off TPF mission, which will attempt to photograph distant planets and study their sizes, positions, and atmospheres.
The Kepler team’s greatest challenge will be deciphering the reams of data its spacecraft beams back. Gregory Henry, an astronomer at Tennessee State University, says that the tough part will be differentiating between a small planet and stellar variability, or detecting the existence of a nearby binary that is subtly eclipsing the target star. Small dead suns circling active stars also could fool Kepler. And many small planets won’t cross between their sun and the spacecraft.
The way to resolve the problems is by doing intensive ground-based observations to determine with precision the movement of each star, its mass, and its rotation speed to ensure that the dimming effect is in fact caused by a planet. “I see no showstoppers,” says Henry, “but it will be difficult to interpret the results.” Borucki insists that his scientific team, which includes many astronomers with access to large telescopes, is aware of the interpretation tangles. Cullers says that SETI is already excited to use Kepler’s data.
If imitation is the sincerest form of flattery, then Kepler should no longer be considered an oddball program run by a maverick. Two ground-based international networks, Transits of Extrasolar Planets and Optical Gravitational Lensing Experiment, have used the transit method to find evidence of planets, though all have been substantially larger than Earth. Last January, OGLE announced the discovery of yet another Jupiter-size planet, this one 5,000 light-years away—the most distant found—with an orbit of just 29 hours and surface temperatures that probably reach 3,000 degrees Fahrenheit.
Borucki is confident there are plenty of smaller, more hospitable worlds in our galaxy, but is mindful that finding extrasolar life is the ultimate goal. “The next step is to go there and join the club of intelligence” or, he believes, if no other terrestrial planets are found, accept the idea that we are likely the lone sentient beings in the Milky Way. “This is like Columbus,” he says of Kepler’s search. “How much would you pay to be part of that expedition—to be first?”
European researchers are laying plans for two photometric space missions as well. The first, called COROT, would be able to spot only planets 10 times larger than Earth. Its 2004 launch date, however, is in question due to budget troubles. The other mission is a more formidable competitor for Kepler. Dubbed Eddington, after British astrophysicist Arthur Eddington, whose measurements of gravitationally bent starlight confirmed Einstein’s general relativity theory, it will also look at Cygnus and study its distant stars for potential terrestrial companions.
Compared to Kepler, Eddington, slated for a 2008 launch, won’t last as long or image as many stars, and those involved are quite aware that Borucki’s team has a jump on them and an excellent chance of finding planets. However, Europe has excelled in extrasolar planetary detection, and researchers there are loathe to give up the early lead. “The Kepler team has put years of effort into ensuring that all aspects are understood,” says Alan Penny, an Eddington team member based at Britain’s Rutherford Appleton Laboratory. He warns, however, that launch dates can change—a polite hint that Europe could try to scoop Kepler.