Dissipation Timescale of Gas Disk

A protoplanetary disk dissipates on the time scale of 3 Myr (Haisch et al. 2001; Hillenbrand 2006 for review). A disk dissipates either by the photoevaporation or by the planet formation (including grain growth in a broad sense). To understand how a disk dissipates is to understand how lucky we are being in the solar system. If the disk dissipates as the consequence of planet formation, our being here might be a part of destiny. If a star can evaporate a disk by itself, a forming planet would have had to compete with time to accrete the disk material before it is gone. Only those systems that make it in time will survive. It could be a shear luck that brought us to a successful system.