Extra-solar planets

Abstract

The discovery of the first extra-solar planet surrounding a main-sequence star was announced in 1995, based on very precise radial velocity (Doppler) measurements. A total of 34 such planets were known by the end of March 2000, and their numbers are growing steadily. The newly discovered systems confirm some of the features predicted by standard theories of star and planet formation, but systems with massive planets, having very small orbital radii and large eccentricities, are common and were generally unexpected.Other techniques being used to search for planetary signatures include accurate measurement of positional (astrometric) displacements, gravitational microlensing and pulsar timing, the latter resulting in the detection of the first planetary mass bodies beyond our solar system in 1992. The transit of a planet across the face of the host star provides significant physical diagnostics, and the first such detection was announced in 1999. Protoplanetary disks, which represent an important evolutionary stage for understanding planet formation, are being imaged from space. In contrast, direct imaging of extra-solar planets represents an enormous challenge. Long-term efforts are directed towards infrared space interferometry, the detection of Earth-mass planets, and measurement of their spectral characteristics.Theoretical atmospheric models provide predictions of planetary temperatures, radii, albedos, chemical condensates and spectral features as a function of mass, composition and distance from the host star. Efforts to characterize planets occupying the 'habitable zone', in which liquid water may be present, and indicators of the presence of life are advancing quantitatively.

Where Are the Massive Close-in Extrasolar Planets?

“…Vol. 568 (Perryman 2000). The lack of small planets at AU is caused by observational selection effects.…”

Survey for Transiting Extrasolar Planets in Stellar Systems. III. A Limit on the Fraction of Stars with Planets in the Open Cluster NGC 1245

“…These empirical constraints will eventually decide the ubiquity or rarity of planetary bodies in the universe. A variety of techniques exist to detect extrasolar planets (Perryman 2000), and there are currently 168 extrasolar planet discoveries. 4 Most of the extrasolar planets have been discovered using the radial velocity technique.…”

How does disk gravity really influence type-I migration?

“…Interactions between a gaseous disk and embedded protoplanetary cores could be decisive to understand the distribution of semi-major axis, eccentricities and masses of extra-solar giant planets (Perryman 2000;Schneider 2004). Exchanges of angular momentum can efficiently operate through the excitation of spiral density waves at the sites of Lindblad resonances, leading to inward migration of solid bodies (Goldreich & Tremaine 1979, 1980Ward 1997).…”