  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.
