NASA’s Cassini spacecraft discovered that Enceladus,
a small moon circling Saturn, has dozens of icy
geysers erupting from cracks near its south pole
that shoot plumes of mineral-laden water ice
and water vapour into space. Cassini’s science
instruments also detected a global, salty ocean
underneath Enceladus’ icy crust that is the source
of these geysers. This moon, only 480 kilometres
(300 miles) across, is extremely cold and should
have frozen solid long ago. However, something
is keeping the ocean from freezing and turning
Enceladus into a frozen ball of ice.
One explanation is that Enceladus’ orbit is not
a perfect circle, but is slightly eccentric, movingEnceladus closer to and farther from Saturn as it
orbits the planet. This slight difference in distance to
Saturn results in a tidal flexing of Enceladus, heating
its interior. Perhaps the key to additional heat may
lie in Enceladus’ core. If this core is not solid, rocky
material, but is instead porous, it could allow water
to circulate through it. Tidal flexing could then cause
rocky material to grind together, generating frictional
heat that heats the water and creates hot spots on
the ocean floor. All this excess heat helps maintain
Enceladus’ liquid-water ocean.
Linda Spilker is project scientist of
NASA’s Cassini mission that explored
the Saturnian systemWhy hasn’t Enceladus
frozen over yet?
NASA’s Cassini
spacecraft was
the last man-
made object to
visit EnceladusMOONSASK
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