2 - Statistical properties of exoplanets

Summary

Since the detection a decade ago of the planetary companion of 51 Peg, more than 200 extrasolar planets have been unveiled by radial-velocity measurements. They present a wide variety of characteristics such as large masses with small orbital separations, high eccentricities, period resonances in multi-planet systems, etc. Meaningful features of the statistical distributions of the orbital parameters or parent stellar properties have emerged. We discuss them in the context of the constraints they provide for planet-formation models and in comparison to Neptune-mass planets in short-period orbits recently detected by radial-velocity surveys, thanks to new instrumental developments and adequate observing strategy. We expect continued improvement in velocity precision and anticipate the detection of Neptune-mass planets in longer-period orbits and even lower-mass planets in short-period orbits, giving us new information on the mass distribution function of exoplanets. Finally, the role of radial-velocity follow-up measurements of transit candidates is emphasized.

Motivation and context

The hypothesis of the formation of planets in our Solar System from a solar nebula, in a flattened gaseous disc in differential rotation, is more than two centuries old. This approach was first proposed by Kant around 1755 and then developed by Laplace (1796). The idea came in a natural way from the observation of the planet configuration in our Solar System: they turn in the same direction, on quasi-circular orbits, in a quasi-common plane.