The Curious Case of 55 Cancri e

The interior of the super-Earth 55 Cancri e is uniquely coupled to its high dayside surface temperature (more than 2000 K) and day-to-nightside gradient (600 K to 800 K). Such differences will lead to longitudinally-varying convective vigor: weaker near the substellar point and stronger near the anti-substellar point (Ra_as ≈ 10 Ra_s). The long-term stability of such an arrangement is uncertain and is further complicated by the generation of interior heat via radioactivity and tides. Such heat will tend to trap in areas of weak convection. Subsequent warming will increase convective vigor and decrease dissipation leading to feedback loops that may differ from one side of the planet to the other. We study this complex interior with an eye towards 55 Cnc e's four companion planets. These sister worlds could tug on 55 Cnc e's orbit and cause it to enter a state (high eccentricity and/or inclination) that will lead to tidal flexure. Its blazing fast 18-hour orbit will enhance dissipation and, in theory, favor rapid circularization and synchronization. It is the apparent observation of a non-zero eccentricity that motivates our reasoning that there may indeed be resonances, or at least perturbations, influencing the 55 Cnc system. We show that the exact location where tidal energy is deposited may couple to 55 Cnc e's bizarre interior in a surprising way. Tides focus on low-viscosity regions with little partial melt, therefore, in the absence of liquid dissipation, we hypothesize that 55 Cnc e will have higher dissipation in its anti-substellar point and along its terminator. Finally, we are motivated by work such as that done by Leconte (2018) which leads us to speculate that 55 Cnc e may be reorienting on geologic timescales. Such reorientations would expose new mantle material to convective and tidal forces. The stability of several spin-orbit resonances could be influenced by reorientations, depending upon their magnitude, with resulting changes to tidal heating. Any triaxiality caused by the melting of 55 Cnc e will only enhance the number and severity of such spin-orbit resonances through librational heating. The lessons learned from 55 Cnc e should be just as applicable to other short-period super-Earths in multi-planet systems, and may lead to new detectable signatures of interior processes.