Uranus and Neptune may not be the icy worlds we’ve long imagined. A new Swiss-led study uses innovative hybrid modeling to reveal that these planets could just as easily be dominated by rock as by water-rich ices. The findings also help explain their bizarre, multi-poled magnetic fields and open the door to a wider range of possible interior structures. But major uncertainties remain, and only future space missions will be able to uncover what truly lies beneath their blue atmospheres.