The search for life in the solar system took a twist Thursday with the announcement that Europa, a moon of Jupiter first discovered by Galileo, shows signs of water geysers erupting from its south pole.

This could be the best evidence yet that Europa has a subsurface ocean. With liquid water and energy from the moon's internal tidal forces, Europa could fit the scientific definition of a habitable world, a place where life could exist, dark and chilly though that existence might be.

The hidden ocean has long been suspected, but scientists have never seen anything as dramatic and overt as plumes of water vapor more than 150 km high. If this finding holds up, it will boost Europa even further as a target for robotic exploration.