On the planet and the disk of CoKu Tauri/4

Spitzer observations of the young star CoKu Tau/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 timescale needed to accrete the inner disk, creating the now detectable hole. The planet migration timescale 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 submegayear 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.