SIMBAD references

In this paper we present the guidelines for an extrasolar planet taxonomy. The discovery of an increasing number of extrasolar planets showing a vast variety of planetary parameters, such as Keplerian orbital elements, and environmental parameters, such as stellar masses, spectral types, and metallicity, prompts the development of a planetary taxonomy. In this work, via principal component analysis followed by hierarchical clustering analysis, we report the definition of five robust groups of planets. We also discuss the physical relevance of such analysis, which may provide a valid basis for disentangling the role of the several physical parameters involved in the processes of planet formation and subsequent evolution. For instance, we were able to divide the hot Jupiters into two main groups on the basis of their stellar masses and metallicities. Moreover, for some groups, we find strong correlations among metallicity, semimajor axis, and eccentricity. The implications of these findings are discussed.