Precise radial-velocity measurements with the HARPS spectrograph reveal the presence of two planets orbiting the solar-type star HD 45364 .
The companion masses are m \sin i = 0.187 M _ { Jup } and 0.658 M _ { Jup } , with semi-major axes of a = 0.681 AU and 0.897 AU , and eccentricities of e = 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 .