2012). These studies reveal the interesting fact that the resonant capture occurs easily if the low-mass planet is on the internal and the gas giant on the external orbit around a solar-type star. This is no longer true if the planet locations will be inverted (Podlewska and Szuszkiewicz 2009; Podlewska-Gaca buy SIS3 et al. 2012). If the super-Earth is orbiting its host star outside the gas giant orbit, then the outgoing wave excited by the gas giant prevents the situation in which the super-Earth can approach

the gas giant closely enough for the first order commensurability to occur. The explanation of the mechanism can be found in Podlewska-Gaca et al. (2012). The candidate for a planet with mass of about 15 m  ⊕  announced in Maciejewski et al. (2010) and located close to the external 2:1 commensurability with a gas giant, if confirmed, could be an ideal test for this newly found migration scenario. Disruption of the Resonances

There are several processes which might lead to disruption of the resonance. The absence of the resonance can be indicative of a dynamical history dominated by gravitational planet-planet scattering (Raymond et al. 2008). selleckchem Let us shortly discuss two of the plausible processes which definitely will play a role in unlocking planets from resonances. These are turbulence and tidal circularization. Role of Turbulence in Unlocking Planets from Resonances Turbulence has a significant impact on the capture of two planets in the Earth mass range into the mean-motion resonance and affects the maintenance of the resonant configurations (Adams et al. 2008; Rein science and Papaloizou 2009; Ketchum et al. 2011). The torques due to turbulent fluctuations have been studied successfully using magnetohydrodynamical simulations (e.g., Nelson and Papaloizou 2004; Laughlin et al. 2004; Nelson 2005; Oishi et al. 2007). Recently, Pierens et al. (2011)

presented the results of their study of the evolution of a system composed of two low-mass planets embedded in a typical turbulent protoplanetary disc. They concluded that in such discs the mean-motion resonances are likely to be disrupted by stochastic density fluctuations. The Role of Tidal Circularization in Unlocking Planets from Resonances The tidal circularization of the orbits induced by the tidal interaction with the central star together with later close scatterings and mergers tended to cause the system to move away from earlier established commensurabilities to an extent determined by the effectiveness of these processes. A high fraction of exoplanetary SB431542 order systems may be near but not actually in resonance (Veras and Ford 2012). Two of such examples have been investigated by Papaloizou and Terquem (2010), namely GJ 581 and HD 40307.