Theories of planetary formation: constraints from the study of meteorites

Compositional variations between chondrite groups and the inventory of short–lived nuclides once present in them are consistent with an origin in the accretion disc of a T Tauri protosun. T Tauri outbursts reprocessed infalling matter, part of which was recycled back into the disc. Chondrites and rapidly cooled igneous meteorites together form the basis of a chronology of events over the first 50 Myr of Solar System history. Chondrites contain evidence of hypervelocity impact within 2 Myr of the formation of the Solar System. This requires the local presence of a Jupiter–massed object to pump up relative velocities. Capture of an interstellar cloudlet, which subsequently underwent gravitational collapse, or of an unbound planet is implied. Capture at a low inclination and high eccentricity would have stirred the matter in the accretion disc, triggered planetesimal formation and growth, stabilized the orbit of the proto–Jupiter, and ended the T Tauri phase of the protosun.