The global properties of the 101 extrasolar planets (or exoplanets for short) so far discovered, which include 88 single-planets and 11 multiple-planet systems, are discussed and compared with our standard ideas of planet formation, as have been developed for explaining the main features of our solar system. The discovered exoplanets have masses around that of Jupiter or larger but, in sharp contrast with Jupiter, most of them are close to their central stars and have large eccentricities. The different alternatives that could explain why the discovered exoplanets have orbital properties so different from those of the Jovian planets are analyzed, as well as the dynamical stability of multiple planet systems, in particular those having two planets locked in the 2:1 mean-motion resonance. Since the current most widely used search technique (spectroscopy) strongly favors the discovery of massive planets close to their central stars, it is possible that they are very weird cases, uncommon in comparison with regular planetary systems like ours.
Basic Space Sciences
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