The Disk Substructures at High Angular Resolution Project (DSHARP): II.
  Characteristics of Annular Substructures
  The Disk Substructures at High Angular Resolution Project used ALMA to map
the 1.25 millimeter continuum of protoplanetary disks at a spatial resolution
of ~5 au. We present a systematic analysis of annular substructures in the 18
single-disk systems targeted in this survey. No dominant architecture emerges
from this sample; instead, remarkably diverse morphologies are observed.
Annular substructures can occur at virtually any radius where millimeter
continuum emission is detected and range in widths from a few au to tens of au.
Intensity ratios between gaps and adjacent rings range from near-unity to just
a few percent. In a minority of cases, annular substructures co-exist with
other types of substructures, including spiral arms (3/18) and crescent-like
azimuthal asymmetries (2/18). No clear trend is observed between the positions
of the substructures and stellar host properties. In particular, the absence of
an obvious association with stellar host luminosity (and hence the disk thermal
structure) suggests that substructures do not occur preferentially near major
molecular snowlines. Annular substructures like those observed in DSHARP have
long been hypothesized to be due to planet-disk interactions. A few disks
exhibit characteristics particularly suggestive of this scenario, including
substructures in possible mean-motion resonance and "double gap" features
reminiscent of hydrodynamical simulations of multiple gaps opened by a planet
in a low-viscosity disk.
