  The vestiges of planet formation have been observed in debris disks harboring
young and massive gaseous giants. The process of giant planet formation is
terminated by the dissipation of gas in the protoplanetary disk. The gas-rich
disk around HD142527 features a small inner disk, a large gap from \sim10 to
\sim140AU, and a massive outer disk extending out to \sim300AU. The gap could
have been carved-out by a giant planet. We have imaged the outer regions of
this gap using the adaptive-optics camera NICI on Gemini South. Our images
reveal that the disk is dynamically perturbed. The outer boundary of the
roughly elliptical gap appears to be composed of several segments of spiral
arms. The stellar position is offset by 0.17+-0.02" from the centroid of the
cavity, consistent with earlier imaging at coarser resolutions. These transient
morphological features are expected in the context of disk evolution in the
presence of a perturbing body located inside the cavity. We perform
hydro-dynamical simulations of the dynamical clearing of a gap in a disk. A
10Mjup body in a circular orbit at r = 90AU, perturbs the whole disks, even
after thousands of orbits. By then the model disk has an eccentric and
irregular cavity, flanked by tightly wound spiral arms, but it is still
evolving far from steady state. A particular transient configuration that is a
qualitative match to HD142527 is seen at 1.7Myr.
