We report a time-series analysis of the O4 I ( n ) fp star \zeta~ { } \mbox { Pup } , based on optical photometry obtained with the SMEI instrument on the Coriolis satellite , 2003–2006 . A single astrophysical signal is found , with P = 1.780938 \pm 0.000093 d and a mean semi-amplitude of 6.9 \pm 0.3 mmag . There is no evidence for persistent coherent signals with semi-amplitudes in excess of \sim 2 mmag on any of the timescales previously reported in the literature . In particular , there is no evidence for a signature of the proposed rotation period , \sim 5.1 days ; \zeta Pup is therefore probably not an oblique magnetic rotator . The 1.8-day signal varies in amplitude by a factor \sim 2 on timescales of 10–100d ( and probably by more on longer timescales ) , and exhibits modest excursions in phase , but there is no evidence for systematic changes in period over the 1000-d span of our observations . Rotational modulation and stellar-wind variability appear to be unlikely candidates for the underlying mechanism ; we suggest that the physical origin of the signal may be pulsation associated with low- \ell oscillatory convection modes .