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.