NASA's Cassini spacecraft discovered a giant plume of water gushing from cracks in the surface near the south pole of Saturn's moon Enceladus in 2005, indicating that there was a reservoir of water beneath the ice. Cassini data also suggest that the south polar has been continuously releasing about 13 billion watts of energy. But how does Enceladus stay warm enough to maintain liquid water underground?
In smaller moons like Enceladus, the cache of radioactive elements usually is not massive enough to produce significant heat for long. So, scientists have considered the role of tidal heating – the gravitational pull from Saturn as Enceladus orbits the planet – as a way to keep Enceladus warm enough for liquid water to remain under its surface.
Scientists with the Cassini team have compared a map of the gravitational tidal stress on the icy crust of Enceladus to a map of the warm zones created using Cassini's composite infrared spectrometer instrument. Areas with the most stress should overlap the warmest zones on the CIRS map, but they don't exactly match.
Terry Hurford, of NASA's Goddard Space Flight Center, Greenbelt, Md., and his team believe the discrepancy can be resolved if Enceladus' rotation rate is not uniform – if it wobbles slightly as it rotates.
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The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency, and the Italian Space Agency. NASA's Jet Propulsion Laboratory, Pasadena, Calif., a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The composite infrared spectrometer team is based at NASA Goddard, where the instrument was built.