Time scale of disk and planet formation

[[abstract]]We review the current theories and observations of the formation of Sun-like stars and protoplanetary disks in distributed and clustered environments. The astrophysical estimates for the temporal durations of various phases of the process are calibrated by theoretical calculations of pre-main sequence contraction tracks for T Tauri stars, a task which is fairly firmly grounded at present. Meteoritical estimates for the ages of the parent bodies of various chondritic components are somewhat compromised by uncertainties concerning whether the 26Al that was alive at the origin of the Solar System was seeded by external nucleosynthetic events or created by internal bombardment via protosolar cosmic rays In either case, however, planetesimal formation in the solar nebula probably did not extend for longer than three million years. The gaseous component of isolated protoplanetary disks may last approximately ten million years, although systems born in clustered environments close to O stars could lose their disks in a million years or less. Planet formation may be difficult in such circumstances.[[fileno]]2010118010037[[department]]物理