Hi All

Tom, Pluto and Charon are synchronised, so no tides. Studies of visible markings on Pluto confirmed this about a decade ago.

Chris, Pluto/Charon is probably a fission-binary. At some point a massive collision gave the original body enough of a kick to send it spinning off into space and to ultimately fission - probably making a few big KBOs in the process, which took excess momentum out of the binary system. Even though Pluto is a tiny fraction of Earth's mass the close separation between the two meant humungous tides - the two were probably like slush until Charon circularised its orbit. But such tidal dissipation would have been rapid and since then I imagine Pluto and Charon have chilled. However because Pluto has a lot of silicates there may have been residual energy stored in the core to cause some localised cryovolcanism. Plus any big impactors would have left long-lasting melt-water lakes under relatively thin ice blanket layers.

But it's anyone's guess how long ago this all happened.

Adam