text: Lightcurve data for Europa has been particularly tricky to interpret , so much so that for a long time its period of rotation was in dispute ( ranging from 5 and a half hours to 11 hours ) , despite numerous observations .
simplified: Lightcurve data for Europa has been very hard to interpret , so much so for a long time its period of rotation was in dispute ( 5 and a half , or 11 hours ? )