What Can Extrasolar Planets Tell Us About Our Solar System

Charles H. Lineweaver, Daniel Grether & Marton HidasSchool of Physics, University of New South Wales and theAustralian Centre for Astrobiology, Sydney, Australiacharley@bat.phys.unsw.edu.auAbstract. We update our analysis of recent exoplanet data that givesus a partial answer to the question: How does our solar system compareto the other planetary systems in the universe? Exoplanets detectedbetween January and August 2002 strengthen the conclusion that Jupiteris a typical massive planet rather than an outlier. The trends in detectedexoplanets do not rule out the hypothesis that our solar system is typical.They support it.1. Identifiable Trends in Extrasolar Planet DataDespite the fact that massive planets are easier to detect, the mass distribu-tion of detected planets is strongly peaked toward the lowest detectable masses.And despite the fact that short period planets are easier to detect, the pe-riod distribution is strongly peaked toward the longest detectable periods. InLineweaver & Grether (2002, hereafter LG) we quantified these trends as accu-rately as possible. Here we update this analysis by including the 27 exoplanetsdetected between January and August 2002. As in LG, we identify a less-biasedsubsample of exoplanets (thick rectangle of Figure 1). Within this subsample,we correct for completeness and then quantify trends in mass and period (Figure 2) that are less biased than trends based on the full sample of exoplanets.Straightforward extrapolations of these trends, into the area of parameter spaceoccupied by Jupiter, indicates that Jupiter lies in a region densely occupied byexoplanets.Naef et al. (2001) point out that none of the planetary companions detectedso far resembles the giants of the solar system. However, this observational factis consistent with the idea that our solar system is a typical planetary system.Figure 1 shows that selection effects can easily explain the lack of detections ofJupiter-like planets. Exoplanets detected to date can not resemble the planetsof our solar system because the Doppler technique used to detect exoplanets hasnot been sensitive enough to detect Jupiter-like planets. We may be samplingthe tail of a distribution … the only part that we are capable of sampling. If thesun were a target star in one of the Doppler surveys, no planet would have beendetected around it. This situation is about to change.Our analysissuggeststhat Jupiter ismoretypical than indicated by previousanalyses, including our own (LG). For example, in Figure 2, our α = −1.6 slopeis slightly steeper than the α = −1.5 found in LG and is steeper than the161