64 outburst times of Comet 29P in 2002–2014 identified and unique periodicity found.
Rotation rate of 29P’s nucleus is extremely slow (mean solar day = 57.71 ± 0.06 d).
Activity is seasonal with a large fraction of the nucleus inactive during 2010–2014.
Outburst mechanism outlined involving subsurface melting and CO/N2 gas ex-solution.
Heats of solution of CO and N2 gas provide a key internal source of thermal energy.