  To understand how the multitude of planetary systems that have been
discovered come to be, we need to study systems at different evolutionary
stages, with different central stars but also in different environments. The
most challenging environment for planet formation may be the harsh UV radiation
field of nearby massive stars which quickly erodes disks by external
photo-evaporation. We have observed the AT Pyx system, located in the head of a
cometary globule in the Gum Nebula, to search for signs of ongoing planet
formation. We used the extreme adaptive optics imager VLT/SPHERE to observe AT
Pyx in polarized light as well as total intensity in the J, H and K-band.
Additionally we employed VLT/NACO to observe the system in the L-band. We
resolve the disk around AT Pyx in scattered light across multiple wavelengths.
We find an extended (>126 au) disk, with an intermediate inclination between 35
deg and 42 deg. The disk shows complex sub-structure and we identify 2 and
possibly 3 spiral-like features. Depending on the precise geometry of the disk
(which we can not unambiguously infer from our data) the disk may be eccentric
with an eccentricity of ~0.16 or partially self-shadowed. The spiral features
and possible eccentricity are both consistent with signatures of an embedded
gas giant planet equal in mass to Jupiter. Our own observations can rule out
brown dwarf companions embedded in the resolved disk, but are not sensitive
enough to detect gas giants. AT Pyx is the first disk in a cometray globule in
the Gum Nebula which is spatially resolved. By comparison with disks in the
Orion Nebula Cluster we note that the extension of the disk may be exceptional
for this environment if the external UV radiation field is comparable to other
cometary globules in the region. The signposts of ongoing planet formation are
intriguing and need to be followed up with higher sensitivity.
