Snow-lines can be thermally unstable

Abstract

Volatile species in protoplanetary discs can undergo a phase change from vapour to solid. These "snow-lines" can play vital roles in planet formation at all scales, from dust coagulation to planetary migration. In the outer regions of protoplanetary discs, the temperature profile is set by the absorption of reprocessed stellar light by the solids. Further, the temperature profile sets the distribution of solids through sublimation and condensation at various snow-lines. Hence the snow-line position depends on the temperature profile and vice-versa. We show that this coupling can be thermally unstable, such that a patch of the disc at a snow-line will produce either run-away sublimation or condensation. This thermal instability arises at moderate optical depths, where heating by absorption of reprocessed stellar light from the disc's atmosphere is optically thick, yet cooling is optically thin. Since volatiles in the solid phase drift much faster than volatiles in the vapour phase, this thermal instability results in a limit-cycle. The snow-line progressively moves in, condensing volatiles, before receding, as the volatiles sublimate. Using numerical simulations, we study the evolution of the CO snow-line. We find the CO snow-line is thermally unstable under typical disc conditions and evolves inwards from $\sim 50$ to $\sim 30$~AU on timescales from 1,000-10,000 years. The CO snow-line spends between $\sim 10\%-50\%$ of its time at smaller separations, where the exact value is sensitive to the total opacity and turbulent viscosity. The evolving snow-line also creates ring-like structures in the solid distribution interior to the snow-line. Multiple ring-like structures created by moving snow-lines could potentially explain the sub-structures seen in many {\it ALMA} images.

Accepted for publication in MNRAS

References in corpus (17)

• Coagulation, fragmentation and radial motion of solid particles in protoplanetary disks
• Gas- and dust evolution in protoplanetary disks
• Evidence of fast pebble growth near condensation fronts in the HL Tau protoplanetary disk
• Global simulations of protoplanetary disks with ohmic resistivity and ambipolar diffusion
• Towards Chemical Constraints on Hot Jupiter Migration
• Grain Retention and Formation of Planetesimals near the Snow Line in MRI-driven Turbulent Protoplanetary Disks
• Chemical enrichment of giant planets and discs due to pebble drift
• Mass measurements in protoplanetary disks from hydrogen deuteride
• Protoplanetary disk rings and gaps across ages and luminosities
• Planet-forming material in a protoplanetary disc: the interplay between chemical evolution and pebble drift
• Can grain growth explain transition disks?
• Fingerprints of giant planets in the composition of solar twins
• Mass constraints for 15 protoplanetary disks from HD 1-0
• Dwarf Nova Outbursts with Magnetorotational Turbulence
• Accreting planets as dust dams in `transition' discs
• Structure of Passive Circumstellar Disks: Beyond the Two-Temperature Approximation
• Importance of thermal diffusion in the gravo-magnetic limit cycle

Cited by in corpus (7)

• Global Three-Dimensional Simulations of Outer Protoplanetary Disks with Ambipolar Diffusion
• Warm millimetre dust in protoplanetary discs near massive stars
• High resolution observations of molecular emission lines toward the CI Tau proto-planetary disc: planet-carved gaps or shadowing?
• Extreme Pebble Accretion in Ringed Protoplanetary Discs
• Giant planet migration during the disc dispersal phase
• The Prospects for Hurricane-like Vortices in Protoplanetary Disks
• Formation of super-Earths in icy dead zones around low-mass stars