the.com/subsurface ocean
a whole sea hiding under a moon's ice like a secret nobody bothered to keep.
means a liquid water layer trapped beneath a planet or moon's frozen or rocky crust, kept warm by tidal squeezing or radioactive heat instead of sunlight.
from the idea surfaced when voyager and galileo spacecraft spotted europa's cracked, ice-rafted surface in the 1990s and geologists realized only a liquid layer beneath could explain the shifting plates.
europa's oceanholds roughly twice earth's total ocean water
heat sourcetidal flexing from jupiter's gravity, not the sun
candidateseuropa, enceladus, titan, ganymede, pluto all qualify
enceladus proofgeysers spray ocean water straight into space