Extrasolar giant planets: Masses and luminosities from in-situ formation theories

Their expected luminosities make young giant planets favorable For the first direct detection of an extrasolar planet. The giant planet formation process is relatively slow with expected formation times ranging from comparable to the star formation timescale up to the nebula lifetime, depending on the formation theory. Therefore quantitative models of giant planet formation have to be considered when estimating young giant planet properties at pre-main sequence stellar ages. This is especially important for free-floating giant planet candidates where planetary nature is inferred from luminosities, without independent mass determinations. I will discuss observables of young- and proto-giant planets as they follow from the disk-instability and nucleated-instability hypothesis, respectively. The luminosity exceeds 10(-4) L., even for a Saturn-mass protoplanet, during the brief, 310(4) year period around maximum accretion. Luminosity maxima of giant planets occur at ages of 1-10 Myr, depending on the details of the formation process. To infer planetary nature in a young population, the properties of young planets have to be compared to those of proto brown dwarfs, as they follow from the respective formation theories.