CO snowline migration through planet-forming regions

Astronomy Unit Seminars
Olja Panic
Sijme-Jan Paardekooper
October 2nd, 2015 at 14:30
GO Jones Room 610

The location in a protoplanetary disc where the temperature drops below freezing for the CO molecule (20K), is believed to foster grain growth and has recently been suggested as the site for formation of planets like Uranus and Neptune. This snowline is expected to host a build-up of ices and sharp chemical gradients in both gas and ice composition. In contrast to the H2O snowline where viscous heating may be dominant, the
CO snowline location is dictated by irradiative heating of the disc by the central star. This is closely related to the gas pressure, the efficiency with which dust couples to the gas, and the dust optical properties.

We investigate the effects that the key evolution processes have on the disc temperature by calculating self-consistent physical structures of discs undergoing gas loss, grain growth, clearing of the inner regions and viscous spreading. We find that over the few-10 Myr lifetime of a disc, the temperature decreases drastically as a result of gas loss. This causes the CO snowline to migrate inward by as much as 100 AU. The possibility to image the CO snowline with ALMA thus presents an exciting opportunity to probe the degree of disc dispersal, and possibly constrain the timescale of this process. Our result also implies that the specific chemical and physical conditions for planet formation found at the CO snowline can occur at different locations, allowing for planets like Uranus and Neptune to form at different distances from the Sun depending on the evolutionary status of the proto-solar nebula at time of their formation.