  The recent ALMA DSHARP survey provided illuminating results on the diversity
of substructures in planet forming disks. These substructures trace
pebble-sized grains accumulated at local pressure maxima, possibly due to
planet-disk interactions or other planet formation processes. DSHARP sources
are heavily biased to large and massive disks that only represent the high
(dust flux) tail end of the disk population. Thus it is unclear whether similar
substructures and corresponding physical processes also occur in the majority
of disks which are fainter and more compact. Here we explore the presence and
characteristics of features in a compact disk around GQ Lup A, the effective
radius of which is 1.5 to 10 times smaller than those of DSHARP disks. We
present our analysis of ALMA 1.3mm continuum observations of the GQ Lup system.
By fitting visibility profiles of the continuum emission, we find substructures
including a gap at ~ 10 au. The compact disk around GQ Lup exhibits similar
substructures to those in the DSHARP sample, suggesting that mechanisms of
trapping pebble-sized grains are at work in small disks as well.
Characteristics of the feature at ~ 10 au, if due to a hidden planet, are
evidence of planet formation at Saturnian distances. Our results hint at a rich
world of substructures to be identified within the common population of compact
disks, and subsequently a population of solar system analogs within these
disks. Such study is critical to understanding the formation mechanisms and
planet populations in the majority of protoplanetary disks.
