  Spitzer observations of the young star CoKuTau/4 reveal a disk with a 10 AU
hole that is most likely caused by a newly formed planet. Assuming that the
planet opened a gap in the viscous disk, we estimate that the planet mass is
greater than 0.1 Jupiter masses. This estimate depends on a lower limit to the
disk viscosity derived from the time scale needed to accrete the inner disk,
creating the now detectable hole. The planet migration time scale must at least
modestly exceed the time for the spectrally inferred hole to clear. The
proximity of the planet to the disk edge implied by our limits suggests that
the latter is perturbed by the nearby planet and may exhibit a spiral pattern
rotating with the planet. This pattern might be resolved with current ground
based mid-infrared cameras and optical cameras on the Hubble Space Telescope.
The required sub-Myr planet formation may challenge core accretion formation
models. However, we find that only if the planet mass is larger than about 10
Jupiter masses, allowing for a high enough surface density without inducing
migration, would formation by direct gravitational instability be possible.

Astrophysics