  A number of Kepler planet pairs lie just wide of first-order mean motion
resonances (MMRs). Tides have been frequently proposed to explain these
pileups, but it is still an ongoing discussion. We contribute to this
discussion by calculating an optimistic theoretical estimate on the minimum
initial eccentricity required by Kepler planets to explain the current observed
spacing, and compliment these calculations with N-body simulations. In
particular, we investigate 27 Kepler systems having planets within 6% of the
2:1 MMR, and find that the initial eccentricities required to explain the
observed spacings are unreasonable from simple dynamical arguments.
Furthermore, our numerical simulations reveal resonant tugging, an effect which
conspires against the migration of resonant planets away from the 2:1 MMR,
requiring even higher initial eccentricities in order to explain the current
Kepler distribution. Overall, we find that tides alone cannot explain planets
close to 2:1 MMR, and additional mechanisms are required to explain these
systems.
