Volume 596, December 2016
|Number of page(s)||5|
|Published online||23 November 2016|
Formation of dust-rich planetesimals from sublimated pebbles inside of the snow line
1 Earth-Life Science Institute, Tokyo
Institute of Technology, Meguro-ku, Tokyo 152-8550, Japan
2 Laboratoire J.-L. Lagrange, Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, 06304 Nice, France
Accepted: 2 November 2016
Context. For up to a few millions of years, pebbles must provide a quasi-steady inflow of solids from the outer parts of protoplanetary disks to their inner regions.
Aims. We wish to understand how a significant fraction of the pebbles grows into planetesimals instead of being lost to the host star.
Methods. We examined analytically how the inward flow of pebbles is affected by the snow line and under which conditions dust-rich (rocky) planetesimals form. When calculating the inward drift of solids that is due to gas drag, we included the back-reaction of the gas to the motion of the solids.
Results. We show that in low-viscosity protoplanetary disks (with a monotonous surface density similar to that of the minimum-mass solar nebula), the flow of pebbles does not usually reach the required surface density to form planetesimals by streaming instability. We show, however, that if the pebble-to-gas-mass flux exceeds a critical value, no steady solution can be found for the solid-to-gas ratio. This is particularly important for low-viscosity disks (α< 10-3) where we show that inside of the snow line, silicate-dust grains ejected from sublimating pebbles can accumulate, eventually leading to the formation of dust-rich planetesimals directly by gravitational instability.
Conclusions. This formation of dust-rich planetesimals may occur for extended periods of time, while the snow line sweeps from several au to inside of 1 au. The rock-to-ice ratio may thus be globally significantly higher in planetesimals and planets than in the central star.
Key words: planets and satellites: formation / planet-disk interactions / accretion, accretion disks
© ESO 2016
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