3 v 2 3 M ay 2 00 2 The Observational Case for Jupiter Being a Typical Massive Planet

We identify a subsample of the recently detected extrasolar planets that is minimally affected by the selection effects of the Doppler detection method. With a simple analysis we quantify trends in the surface density of this subsample in the period-M sin(i) plane. A modest extrapolation of these trends puts Jupiter in the most densely occupied region of this parameter space, thus indicating that Jupiter is a typical massive planet rather than an outlier. Our analysis suggests that Jupiter is more typical than indicated by previous analyses. For example, instead of M Jup mass exoplanets being twice as common as 2 M Jup exoplanets, we find they are three times as common. The prevalence of infrared emission from accretion disks around young stars is consistent with the idea that such disks are ubiquitous. Their disappearance on a time scale of 50 to 100 million years suggests that the dust and gas accrete into planetesimals and eventually planets (Haisch et al. 2001). Such observations support the widely accepted idea that planet formation is a common by-product of star formation (e.g. Beckwith et al. 2000). In the standard model of planet formation, Earth-like planets accrete near the host star from rocky debris depleted of volatile elements, while giant gaseous planets accrete in the ice zones (∼ > 4 AU) around rocky cores (Lissauer 1995, Boss 1995). When the rocky cores in the ice zones reach a critical mass (∼ 10 m Earth) runaway gaseous accretion (formation of jupiters) begins and continues until gaps form in the protoplanetary disk or the disk dissipates (Papaloizou & Terquem 1999, Habing et al. 1999), leaving one or more Jupiter-like planets at ∼ 4 − 10 AU. We cannot yet determine how generic the pattern described above is. However, formation of terrestrial planets is thought to be less problematic than the formation of Jupiter-like planets (Wetherill 1995). Gas in circumstellar disks around young stars is lost within a few million years and it is not obvious that the rocky cores necessary