  The extrasolar planets (EPs) so far detected are very different to the
planets in our own Solar System. Many of them have Jupiter-like masses and
close-in orbits (the so-called hot planets, HPs), with orbital periods of only
a few days. In this paper, we present a new statistical analysis of the
observed EPs, focusing on the origin of the HPs. Among the several HP formation
mechanisms proposed so far, the two main formation mechanisms are type II
migration and scattering. In both cases, planets form beyond the so-called
snow-line of the protoplanetary disk and then migrate inward due to angular
momentum and energy exchange with either the protoplanetary disk or with
companion planets. Although theoretical studies produce a range of observed
features, no firm correspondence between the observed EPs and models has yet
been established. In our analysis, by means of principal component analysis and
hierarchical cluster analysis, we find convincing indications for the existence
of two types of HPs, whose parameters reflect physical mechanisms of type II
migration and scattering.

Earth and Planetary Astrophysics