Protoplanetary discs

An unknown event disturbed the equilibrium of the interstellar cloud, and it collapsed. This process may have been caused by shock waves from a supernova explosion, or by a density wave of a spiral arm of the galaxy. The gas molecules and the particles were compressed, and with increasing compression, both temperature and pressure increased. It is possible that the centrifugal forces due to the rotation of the system prevented a spherical contraction. The result was a relatively flat, rotating disc of matter, in the centre of which was the primeval sun. Analogues of the early solar system, i.e., protoplanetary discs, have been identified from the radiation emitted by T Tauri stars (Koerner, 1997). 

The paramount importance of carbon in the cosmos is shown by the fact that more than 75% of the approximately 120 interstellar and circumstellar molecules so far identified are carbon containing (Henning and Salama, 1998). Molecules apparently travel from the ISM via protoplanetary discs to the planetesimals and from there, via accretion, to the heavenly bodies formed. The molecules so far identified in ISM come from quite different types of compounds ... 

Semenov D, Wiebe D, Henning Th (2004) Reduction of chemical networks. II. Analysis of the fractional ionisation in protoplanetary discs. Astron Astrophys 417 93-106. doi 10.1051/ 0004-6361 20034128... 

Gail H.-P. (2001) Radial mixing in protoplanetary accretion disks I. Stationary disc models with annealing and carbon combustion. Astron. Astrophys. 378, 192-213. 

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