HD 45364: 2 planets in 3:2 resonance.

Abstract wrote:Precise radial-velocity measurements with the HARPS spectrograph reveal the presence of two planets orbiting the solar-type star HD45364. The companion masses are 0.187 Mjup and 0.658 Mjup, with semi-major axes of 0.681 AU and 0.897 AU, and eccentricities of 0.168 and 0.097, respectively. A dynamical analysis of the system further shows a 3:2 mean motion resonance between the two planets, which prevents close encounters and ensures the stability of the system over 5 Gyr. This is the first time that such a resonant configuration has been observed for extra-solar planets, although there is an analogue in our Solar System formed by Neptune and Pluto. This singular planetary system may provide important constraints on planetary formation and migration scenarios.

A newfound pair of extrasolar planets may boost the planetary prospects of beleaguered Pluto. The pair has the same orbital resonance as Neptune and Pluto, and the "inner" planet may sometimes lie beyond the "outer" planet--the same situation that prevails for Neptune and Pluto.