Extrasolar Planetary Systems - Astronomy and （系外行星系统天文学和）.pdf

FEATURE ARTICLE Extrasolar Planetary Systems Observations of distant worlds are beginning to reveal how planetary systems form and evolve Gregory P. Laughlin Christiaan Huygens carried out the first known search for extrasolar planets in the 1600s, but the next three centuries were filled only with false alarms, dashed hopes and nondetections. It took until 1988 before the first hints of progress began to emerge: Gordon A. H. Walker and his colleagues at the University of British Columbia reported evidence for unseen planetary-mass companions orbiting several nearby stars. These investigators were extremely cautious, however, and stated that orbiting planets were just one of several possible interpretations for their data. Consequently, few people took much notice. The following year, David W. Latham of the Harvard-Smithsonian Center for Astrophysics and four colleagues reported strong evidence for what might be a planet orbiting an obscure star known as HD 114762. Because Lathams planet has at least 10 times the mass of Jupiter, astronomers tended to assume that it was either a brown dwarf or a star of very low mass. So it, too, didnt make headlines. In 1992, Alexander Wolsczan of Penn State University and Dale A. Frail of the National Radio Astronomy Observatory used a highly accurate timing method to discover two very small planets in orbit around a pulsar. These utterly bizarre worlds apparently formed from a disk of radioactive debris left over after the supernova explosion that created the pulsar. This strange setting perhaps accounts for why few people felt that a true analog of our solar system had been found. Yet the detection gave the first hint that planet formation is a common and robust process. Then in 1995, two Swiss astronomers, Michel Mayor and Didier Queloz of the Geneva Observatory, stunned the world when they detected a planet circling 51 Pegasi, a nearby star not all that different from the Sun. The planet, they claimed, is ro