  We present high-contrast observations of the circumstellar environment of the
Herbig Ae/Be star HD100546. The final 3.8 micron image reveals an emission
source at a projected separation of 0.48"+-0.04" (corresponding to ~47+-4 AU at
a position angle of 8.9+-0.9 degree. The emission appears slightly extended
with a point source component with an apparent magnitude of 13.2+-0.4 mag. The
position of the source coincides with a local deficit in polarization fraction
in near-infrared polarimetric imaging data, which probes the surface of the
well-studied circumstellar disk of HD100546. This suggests a possible physical
link between the emission source and the disk. Assuming a disk inclination of
~47 degree the de-projected separation of the object is ~68 AU. Assessing the
likelihood of various scenarios we favor an interpretation of the available
high-contrast data with a planet in the process of forming. Follow-up
observations in the coming years can easily distinguish between the different
possible scenarios empirically. If confirmed, HD100546 "b" would be a unique
laboratory to study the formation process of a new planetary system, with one
giant planet currently forming in the disk and a second planet possibly
orbiting in the disk gap at smaller separations.

Astrophysics of Galaxies;Earth and Planetary Astrophysics