Observatoire de Paris
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Artistic reproduction of a hot-Jupiter type extrasolar planet
Copyright : Paris Observatory / UFE

51 Peg b, 47 Uma b and 70 Vir b

In 1995, Michel Mayor and Didier Queloz, from Geneva Observatory, detected a planet around 51 Pegasi using the radial velocity spectroscopy method. This object, with a mass of 0,5 MJ, was so close to its star (0,05 AU, period 4,2  days) that the Swiss researchers were very careful before annoucing their discovery, considered today to be the first detection of an exoplanet around a solar-type star.

The Americans Geoffrey Marcy and Paul Butler, who were running a program similar to the Swiss' one, confirmed the appearance of 51 Pegasi b, and the year after announced two new exoplanets, 47 Ursae Majoris b (3,4 MJ, period 3 years) and 70 Virginis b (6,6 MJ, period 117  days). The orbit of the third planet is very elliptic (eccentricity of 0,4).

The highly elliptic orbits, such as those of giant planets close to their stars like 51 Pegasi b, were not predicted by the theories of the formation of the Solar System.

These discoveries motivate an important theoretical work. In particular, the Migration Phenomenon, proposed in 1980 by Peter Goldreich and Scott Tremaine, is used to explain the presence of 51 Peg b on its current orbit, at a location where it couldn't have formed.