Snow-lines as probes of turbulent diffusion in protoplanetary discs

Abstract

Sharp chemical discontinuities can occur in protoplanetary discs, particularly at `snow-lines' where a gas-phase species freezes out to form ice grains. Such sharp discontinuities will diffuse out due to the turbulence suspected to drive angular momentum transport in accretion discs. We demonstrate that the concentration gradient - in the vicinity of the snow-line - of a species present outside a snow-line but destroyed inside is strongly sensitive to the level of turbulent diffusion (provided the chemical and transport time-scales are decoupled) and provides a direct measurement of the radial `Schmidt number' (the ratio of the angular momentum transport to radial turbulent diffusion). Taking as an example the tracer species N${}_2$H${}^{+}$, which is expected to be destroyed inside the CO snow-line (as recently observed in TW Hya) we show that ALMA observations possess significant angular resolution to constrain the Schmidt number. Since different turbulent driving mechanisms predict different Schmidt numbers, a direct measurement of the Schmidt number in accretion discs would allow inferences about the nature of the turbulence to be made.

arXiv comment6 Pages, 2 Figures, Accepted for publication in ApJL

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Cited by in corpus (8)

• Excess C/O and C/H in outer protoplanetary disk gas
• Probing CO and N${}_2$ Snow Surfaces in Protoplanetary Disks with N${}_2$H${}^{+}$ Emission
• Herbig Stars: A Quarter Century of Progress
• Constraining turbulence in protoplanetary discs using the gap contrast: an application to the DSHARP sample
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• Thermal Behavior of Astrophysical Amorphous Molecular Ices
• Zero Age Planetary Orbit of Gas Giant Planets Revisited: Reinforcement of the Link with Stellar Metallicity
• Formation of Water-rich Giant Planet Satellites at Decretion Disk Ice Lines