SETI Institute Principal Investigator
Astronomer Doug Caldwell looks for evidence of planets around other stars using a survey called the transit method. If a planet happens to pass in front of a star as seen from the Earth, it will block some of the light from the star. “A small fraction of extrasolar planets will be aligned such that the planet passes between its star and the line-of-sight to the Earth,”Caldwell explains. “Careful measurements of the brightness of a star can reveal when one of these line-of-sight crossings, or ‘transits,’ occurs.” The change in the star’s brightness during a transit gives the size of the planet. “During the transit,” he says, “some of the light from the star passes through the outer atmosphere of the planet.” By studying the star’s spectrum during transit, Caldwell seeks to determine the composition of the planet’s atmosphere.
“The ideal place for a transit search is from space, where the Earth’s atmosphere and the rising and setting of the Sun don’t interfere,” he says. “Fortunately, one particular location on Earth approximates many of the advantages of space. The South Pole, with its four-month night and very dark sky, is the best place on Earth to conduct a transit search.” As a member of the Kepler mission, to be launched in 2007, Caldwell will have access to a space-based observatory for detecting transits. Until then, his search for Earth-sized planets will proceed from the next best place, in the southernmost part of Antarctica.
- SETI Institute Explorer, Special Edition 2005