QUESTION: Can HST image Neptune's rings?
ANSWER from Heidi Hammel on March 19th,1996:

It is probably possible to image Neptune's rings with HST.  The main
difference between imaging the planet itself (as past programs have done)
and imaging moons and rings is the choice of filter: planet imaging is done
in selected narrow-band or medium-band filters, to allow better probing of
the planet's vertical cloud structure.  In contrast, searches for rings or
faint moons are done in wide filters, to get as much light as possible.
Nevertheless, some ring investigators are already searching archival Neptune
planet imaging to look for the brightest clumps in the rings (ring arcs).
With something like 9 orbits of broad-band imaging, investigators would have
enough light and enough time-sampling to detect and see orbital motion for
a moon or ring arc.  This will be done sometime in Cycle 6 (between July 96
and July 97), so stay tuned for results.