  A relatively massive and moderately eccentric disk of trans-Neptunian objects
(TNOs) can effectively counteract apse precession induced by the outer planets,
and in the process shepherd highly eccentric members of its population into
nearly-stationary configurations which are anti-aligned with the disk itself.
We were sufficiently intrigued by this remarkable feature to embark on an
extensive exploration of the full spatial dynamics sustained by the combined
action of giant planets and a massive trans-Neptunian debris disk. In the
process, we identified ranges of disk mass, eccentricity and precession rate
which allow apse-clustered populations that faithfully reproduce key orbital
properties of the much discussed TNO population. The shepherding disk
hypothesis is to be sure complementary to any potential ninth member of the
Solar System pantheon, and could obviate the need for it altogether. We discuss
its essential ingredients in the context of Solar System formation and
evolution, and argue for their naturalness in view of the growing body of
observational and theoretical knowledge about self-gravitating disks around
massive bodies, extra-solar debris disks included.
