臨時セミナー
日時	平成11年10月5日（火）１５：３０より
場所	東京工業大学ベンチャービジネスラボラトリー棟
講 演 者：	Geoff Marcy（University of California, Berkeley）
講演題目：	Observations of Planets Around Stars
内容：	Doppler measurements of 500 nearby stars have revealed 20 orbiting companions that have roughly the mass of Jupiter. These highest mass "planets" have masses of 5 times that of our Jupiter. The mass distribution rises from 5 Jupiter-masses toward lower masses, suggesting that we have only detected nature's most massive planets with current techniques. One star, Upsilon Andromedae harbors three Jupiter-mass companions, making it the first planetary system found around another sun-like star. The 5 planets which orbit other stars closer than 0.1 AU from them (1 Earth-Sun distance = 1 AU) all reside in circular orbits, plausibly induced by planetary tides raised by the star. In contrast, all 11 planets that orbit farther than 0.2 AU reside in elliptical orbits, indeed more elliptical than the orbits of Jupiter (e=0.048) and Earth (e=0.03). These elliptical orbits may result from planets that were originally in circular orbits, but perturbed gravitationally by other orbiting planets or by the protoplanetary disk. Our Solar System architecture appears, in retrospect, to represent a low entropy state, with its nine planetary orbits precariously stable in co-planar, circular orbits that have aligned angular momentum vectors. high-entropy planetary systems may represent the norm. Tbe planet-bearing stars are systematically rich in heavy elements (as in the Sun) copared to stars in the Solar neighborhood. This enrichment indicates that planet formation depends sensitively on the abundance of heavy elements. Future planet searches will employ new techniques to detect Saturn-- and Neptune-mass planets. Future instruments may detect other earths.