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Observed Properties of Exoplanets: Masses, Orbits, and Metallicities


We review the observed properties of exoplanets found by the Doppler technique that has revealed 152 planets to date. We focus on the ongoing 18-year survey of 1330 FGKM type stars at Lick, Keck, and the Anglo-Australian Telescopes that offers both uniform Doppler precision (3 m/s) and long duration. The 104 planets detected in this survey have minimum masses (Msini) as low as 6 Earth-masses, orbiting between 0.02 and 6 AU. The core-accretion model of planet formation is supported by four observations: 1) The mass distribution rises toward the lowest detectable masses, dN/dM \propto 1/M. 2) Stellar metallicity correlates strongly with the presence of planets. 3) One planet (1.3 Saturn Masses) has a massive rocky core, M = 70 Earth-masses. 4) A super-Earth of about 7 Earth-masses has been discovered. The distribution of semi-major axes rises from 0.3 -- 3.0 AU (dN/dloga) and extrapolation suggests that about12% of the FGK stars harbor gas-giant exoplanets within 20 AU. The median orbital eccentricity is =0.25, and even planets beyond 3 AU reside in eccentric orbits, suggesting that the circular orbits in our Solar System are unusual. The occurrence ``hot Jupiters'' within 0.1 AU of FGK stars is 1.2%. Among stars with one planet, 14% have at least one additional planet, occasionally locked in resonances. Kepler and COROT will measure the occurrence of earth-sized planets. The Space Interferometry Mission (SIM) will detect planets with masses as low as 3 Earth-masses orbiting within 2 AU of stars within 10 pc, and it will measure masses, orbits, and multiplicity. The candidate rocky planets will be amenable to follow-up spectroscopy by the ``Terrestrial Planet Finder'' and Darwin.

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