The detection algorithms crafted by Jenkins and his colleagues, first identify and remove known sources of stellar oscillation, then uses an adaptive, wavelet-based matched filter to remove the non-white (1/f) noise typical of starlight. As a result, Kepler can accurately measure the minuscule dip in a star's light output when an orbiting planet circles in front of its side facing Earth.
Called the "transit" method, Kepler constantly records the output from over 100,000 stars in its 18 degree field of view, and can typically detect the dip in luminosity caused by an Earth-sized planet with about 6-1/2 hours of observation. Unfortunately, a typical habitable planet circling a solar-like star only orbits it about once a year, and since three transits are needed to verify a planet's presence, Kepler was given a three and half year mission time—six months to spot the 1,235 planets it is now tracking and three more years of constant observation to verify that they indeed are planets and not anomalies. (Other telescopes, including the Spitzer Space Telescope, are also being enlisted to perform the verification task on the 1,235 candidates.)
Once a planet is detected, its signature can be analyzed from the variation in the stars' output—especially when the planet is just passing by the edge of the star at which point its atmosphere can be analyzed for Earth-like qualities. From its period, a planet's orbital size can be calculated as well as the mass of the star (using Johannes Kepler's Third Law, after which the spacecraft was named). The amount of the star's brightness dip reveals the size of the planet, which together with its orbit size and the temperature of the star reveals the temperature of the planet itself.
Artist's rendition of Kepler spacecraft.
Credit: NASA/Kepler mission/Wendy Stenzel
Kepler hardware consists of a nearly one-meter wide Schmidt mirror-style visible-light telescope with a giant image array at its focal point, consisting of 42 charge coupled devices (CCDs) each housing over 2.25 million pixels for a total of 95 mega pixels. To allow constant monitoring, Kepler was put into an orbit that prevents our sun or moon from obstructing its view. And in a final concession to meet its budgetary constraints, its orientation was made single-purpose—Kepler will always point in its current direction, even after it completes its primary mission in November 2012. (However, at current consumption levels, Kepler will likely operate for a total of 10 years).
Now that Kepler has located an abundance of candidates, groups affiliated with the Search for Extraterrestrial Intelligence (SETI) are aiming their radio telescopes specifically at the detected planets to look for sinusoidal waveforms in the 1-to-11 GHz range where nature seems never to tread. In particular, the Allen Telescope Array operated by the SETI Institute plans to begin looking for the trademark signature of alien civilizations starting next month.