  Pluto and its satellites will be the most distant objects ever reconnoitered
when NASA's New Horizons spacecraft conducts its intensive flyby of this system
in 2015. The size-frequency distribution (SFD) of craters on the surfaces in
the Pluto system have long been expected to provide a useful measure of the
size distribution of Kuiper Belt Objects (KBOs) down to much smaller size
scales than presently observed. However, currently predicted escape rates of
Pluto's atmosphere suggest that of order one-half to several kilometers of
nitrogen ice has been removed from Pluto's surface over geologic time. Because
this range of depths is comparable to or greater than most expected crater
depths on Pluto, one might expect that many craters on Pluto's surface may have
been removed or degraded by this process, biasing the observed crater SFD
relative to the production-function crater SFD. Further, if Pluto's surface
volatile layer is comparable to or deeper than crater depths, and if the
viscosity of this layer surface ice is low like the viscosity of pure N2 ice at
Pluto's measured 35 K surface temperature (or as low as the viscosity of CH4
ice at warmer but plausible temperatures on isolated pure-CH4 surfaces on
Pluto), then craters on Pluto may also have significantly viscously relaxed,
also potentially biasing the observed crater SFD and surface crater retention
age. Here we make a first exploration of how these processes can affect the
displayed cratering record on Pluto. We find that Pluto's surface may appear to
be younger owing to these effects than it actually is. We also find that by
comparing Pluto's cratering record to Charon's, it may be possible to estimate
the total loss depth of material from Pluto's surface over geologic time, and
therefore to estimate Pluto's time-averaged escape rate.
