* Astronomy

Title: HD45364, a pair of planets in a 3:2 mean motion resonance
Authors: A.C.M. Correia, S. Udry, M. Mayor, W. Benz, J.-L. Bertaux, F. Bouchy, J. Laskar, C. Lovis, C. Mordasini, F. Pepe, D. Queloz

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.

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