ICY SCIENCE: SCIENCE SPACE ASTRONOMY Spring 2014 | Page 30

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and ice of the southern latitudes make up a physically
active zone that is always renewing itself. Credit: NASA/
JPL/Space Science Institute
The surface on Enceladus seems calm, and for a tiny
moon that seems at first glance to be utterly frozen,
that’s what you’d expect. Except that Enceladus is a
moon of the gas giant planet, Saturn, and Saturn’s
gravity pulls at Enceladus and warps its rocky and icy
layers. Think of it like the way our moon pulls on our
planet - we can see our oceans being pulled along with
the moon in high and low tides. Our moon’s gravity
affects our rocky crust, too, we just don’t really notice
it. But in the case of Enceladus, the gravity pull from
Saturn is so strong that it causes solid layers like ice,
maybe even the rocky core, to stretch and push into
each other. This heats things up and may be the main
cause of the jets.
Of course, Enceladus has its own gravity field which can
affect smaller objects like the Cassini spacecraft and
alter its path. Physicists saw that the gravity measurements Cassini took over the moon’s south polar area
were off from what would be expected if the moon
were a solid ball of rock and ice. The denser something is, the greater its gravity, and over the south pole,
it looked like there was something denser than ice
ICY SCIENCE | QTR 2 SPRING 2014