Roche limit
is the distance within which a celestial body, held together only by its own
gravity, will disintegrate due to a second celestial body's tidal forces exceeding
the first body’s gravitational self-attraction.
Inside the Roche limit, orbiting material will tend to disperse and form rings,
while outside the limit, material will tend to coalesce.
The term is named after Édouard Roche, the french
astronomer who first calculated this limit in 1848
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Examples of Roche limits
Examples of Roche limits
(THE ROCHE LIMIT…)
Generally …large natural bodies orbit beyond their Roche Limit;
exceptions have other adhesive forces binding the object (e.g.
human-made, low-orbit satellites around Earth!)
The (major) rings of Saturn, Jupiter, Neptune and Uranus
are all within their Roche limit
 particles from crushed up former satellites?
Energy generated by tidal movements 
dissipated as heat
Io (Jupiter’s innermost moon) –
tidal forces  internal heat 
powers extreme volcanic
activity
Europa (also Jupiter’s) –
tidal heat  substantial subsurface ocean  dark
biospheres?
..also cryo-volcanism!
e.g. ice
volcanoes on
Saturn’s moon
Enceladus!