  Past computational studies of planet-induced vortices have shown that the
dust asymmetries associated with these vortices can be long-lived enough that
they should be much more common in mm/sub-mm observations of protoplanetary
discs, even though they are quite rare. Observed asymmetries also have a range
of azimuthal extents from compact to elongated even though computational
studies have shown planet-induced vortices should be preferentially elongated.
In this study, we use 2-D and 3-D hydrodynamic simulations to test whether
those dust asymmetries should really be so long-lived or so elongated. With
higher resolution (29 cells radially per scale height) than our previous work,
we find that vortices can be more compact by developing compact cores when
higher-mass planets cause them to re-form, or if they are seeded by tiny
compact vortices from the vertical shear instability (VSI), but not through
dust feedback in 3-D as was previously expected in general. Any case with a
compact vortex or core(s) also has a longer lifetime. Even elongated vortices
can have longer lifetimes with higher-mass planets or if the associated planet
is allowed to migrate, the latter of which can cause the dust asymmetry to stop
decaying as the planet migrates away from the vortex. These longer dust
asymmetry lifetimes are even more inconsistent with observations, perhaps
suggesting that discs still have an intermediate amount of effective viscosity.
