  Extrasolar debris disks are detected by observing dust, which is thought to
be released during planetesimal collisions. This implies that planetesimals are
dynamically excited ("stirred"), such that collisions are sufficiently common
and violent. The most frequently considered stirring mechanisms are
self-stirring by disk self-gravity, and planet-stirring via secular
interactions. However, these models face problems when considering disk mass,
self-gravity, and planet eccentricity, leading to the possibility that other,
unexplored mechanisms instead stir debris. We hypothesize that planet-stirring
could be more efficient than the traditional secular model implies, due to two
additional mechanisms. First, a planet at the inner edge of a debris disk can
scatter massive bodies onto eccentric, disk-crossing orbits, which then excite
debris ("projectile stirring"). Second, a planet can stir debris over a wide
region via broad mean-motion resonances, both at and between nominal resonance
locations ("resonant stirring"). Both mechanisms can be effective even for
low-eccentricity planets, unlike secular-planet-stirring. We run N-body
simulations across a broad parameter space, to determine the viability of these
new stirring mechanisms. We quantify stirring levels using a bespoke program
for assessing Rebound debris simulations, which we make publicly available. We
find that even low-mass projectiles can stir disks, and verify this with a
simple analytic criterion. We also show that resonant stirring is effective for
planets above ~0.5 MJup. By proving that these mechanisms can increase
planet-stirring efficiency, we demonstrate that planets could still be stirring
debris disks even in cases where conventional (secular) planet-stirring is
insufficient.
