ALBERT

Description: Low-mass protostars are the extrasolar analogues of the natal Solar system. Sophisticated physicochemical models are used to simulate the formation of two protoplanetary discs from the initial prestellar phase, one dominated by viscous spreading and the other by pure infall. The results show that the volatile prestellar fingerprint is modified by the chemistry en route into the disc. This holds relatively independent of initial abundances and chemical parameters: physical conditions are more important. The amount of CO 2 increases via the grain-surface reaction of OH with CO, which is enhanced by photodissociation of H 2 O ice. Complex organic molecules are produced during transport through the envelope at the expense of CH 3 OH ice. Their abundances can be comparable to that of methanol ice (few per cent of water ice) at large disc radii ( R 〉 30 au). Current Class II disc models may be underestimating the complex organic content. Planet population synthesis models may underestimate the amount of CO 2 and overestimate CH 3 OH ices in planetesimals by disregarding chemical processing between the cloud and disc phases. The overall C/O and C/N ratios differ between the gas and solid phases. The two ice ratios show little variation beyond the inner 10 au and both are nearly solar in the case of pure infall, but both are subsolar when viscous spreading dominates. Chemistry in the protostellar envelope en route to the protoplanetary disc sets the initial volatile and prebiotically significant content of icy planetesimals and cometary bodies. Comets are thus potentially reflecting the provenances of the midplane ices in the solar nebula.