Europa (moon).

Europa is one of the four Galilean satellites that orbit Jupiter. Only slightly smaller than the Earth’s Moon, Europa is covered by a relatively smooth layer of highly reflective fractured ice. Tidal forces exerted by Jupiter cause internal heating on Europa that apparently results in the periodic resurfacing of watery flows, which have obliterated most impact craters and other blemishes over time. Heat flow may be sufficient to maintain a liquid water subsurface layer that could harbor simple life forms.