The Interesting Dynamics of the 55 Cancri System
  Recent studies of the 55 Cancri system suggest the existence of three planets with periods of ~15 days, ~45 days, and ~5500 days (Marcy et al. 2002). The inner two planets are near the 3:1 mean motion commensurability and it is likely that these two planets became trapped in the resonance while farther from the star and migrated together. As the innermost planet begins to dissipate energy through tides the planets break out of the resonance. The final state of the system gives important information about its past history, such as the migration timescale that led to capture. 
Gregory S. Novak, David Lai, and D. N. C. Lin