“The Use of Transit Timing to Detect Terrestrial-Mass Extrasolar Planets,” by Matthew Holman (Harvard-Smithsonian Center for Astrophysics) and Norman Murray at the University of Toronto, appears in the February 25th issue of Science. The paper covers a new planet-finding technique that studies transit time; i.e., the amount of time it takes a planet to orbit its star. Transit timing studies the variation in apparent stellar brightness caused by the passage of a planet in front of its star as seen from Earth.
Because the timing of the transit will vary depending on the presence of other planets in the system, astronomers should be able to make estimates about the mass of a second planet. And here’s the best part: While the current radial velocity observations that have been used to detect most of the 150 known extrasolar planets cannot be used for terrestrial worlds, this method may just be sensitive enough to detect them. The method has implications for future transit studies, including NASA’s Kepler mission.
The complete reference is Science (25 February 2005), Vol. 307, pp. 1288-1291. The Science paper requires membership in AAAS, but see “The Use of Transit Timing to Detect Extrasolar Planets with Masses as Small as Earth,” available at the ArXiv preprint site (PDF warning).