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Sunspots are cool areas caused by strong surface magnetic fields inhibitingconvection. Moreover, strong magnetic fields can alter the average atmosphericstructure, degrading our ability to measure stellar masses and ages. Stars moreactive than the Sun have more and stronger dark spots than in the solar case,including on the rotational pole itself. Doppler imaging, which has so farproduced the most detailed images of surface structures on other stars than theSun, cannot always distinguish the hemisphere in which the starspots arelocated, especially in the equatorial region and if the data quality is notoptimal. This leads to problems in investigating the north-south distributionof starspot active latitudes (those latitudes with more spot activity), whichare crucial constraints of dynamo theory. Polar spots, inferred only fromDoppler tomography, could plausibly be observational artifacts, casting somedoubt on their very existence. Here we report imaging of the old,magnetically-active star $\zeta$ Andromedae using long-baseline infraredinterferometry. In our data, a dark polar spot is seen in each of two epochs,while lower-latitude spot structures in both hemispheres do not persist betweenobservations revealing global starspot asymmetries. The north-south symmetry ofactive latitudes observed on the Sun is absent on $\zeta$ And, which hostsglobal spot patterns that cannot be produced by solar-type dynamos.

No Sun-like dynamo on the active star $\zeta$ Andromedae from starspot asymmetry