Abstract

The condensation fronts of some of the main molecular species like H2O and CO are points of significant discontinuity for the chemical composition of gas and the fraction of ice in solids. Both properties are crucial in determining whether a planet may form and what atmospheric composition it may have. The location of the CO snowline is determined by both irradiation by the central star and the capability of the disc to capture the stellar photons, while for the H2O snowline accretion is an additional efficient source of heating.

We carried out a grid-based exploration of disc structure models to investigate how disc evolution processes affect the temperature of the planet-forming midplane. We find that as a result of gas loss and grain growth – both known to take place over the several Myr of disc lifetime – snow fronts are pushed closer to the star by 50% or more. If the CO snowline fosters formation of planets like Uranus and Neptune, as suggested recently, our results show that this effect is not limited to a low density outer region of the disc but planets may form progressively at different locations as the CO snowline migrates towards denser regions. This work also implies that the highest value of the C/O ratio in disc gas may be reached much closer to the star than previously thought.

Recently it has been shown that the CO snowline can be imaged using submillimetre interferometric imaging of N2H or DCO in discs. This is a promising method to obtain observational constraints on the physical conditions of planet forming regions in statistically significant samples of discs very soon, considering ALMA sensitivity and resolution.