Light-induced disassembly of dusty bodies in inner protoplanetary discs: implications for the formation of planets

TL;DR

This paper demonstrates that light-induced erosion can disassemble small dusty bodies in inner protoplanetary discs, influencing planet formation by creating dust reservoirs and preventing early planetesimal formation in certain regions.

Contribution

It introduces a novel mechanism of dust erosion via solid-state greenhouse effects and thermophoresis, impacting theories of planetesimal and planet formation.

Findings

Dusty bodies smaller than several kilometers are rapidly disassembled within 0.4 au of the star.

Disassembled dust can be reprocessed and retained in the disc, aiding planet formation.

Erosion occurs even in gas-depleted inner disc regions, affecting planetesimal growth.

Abstract

Laboratory experiments show that a solid-state greenhouse effect in combination with thermophoresis can efficiently erode a dust bed in a low-pressure gaseous environment. The surface of an illuminated, light absorbing dusty body is cooler than the dust below the surface (solidstate greenhouse effect). This temperature gradient leads to a directed momentum transfer between gas and dust particles and the dust particles are subject to a force towards the surface(thermophoresis). If the thermophoretic force is stronger than gravity and cohesion, dust particles are ejected. Applied to protoplanetary discs, dusty bodies smaller than several kilometres in size which are closer to a star than about 0.4 au are subject to a rapid and complete disassembly to submillimetre size dust aggregates by this process. While an inward-drifting dusty body is destroyed, the generated dust is not lost for the disc by sublimation or subsequent accretion on to the star but can be reprocessed by photophoresis or radiation pressure. Planetesimals cannot originate through aggregation of dust inside the erosion zone. If objects larger than several kilometres already exist, they prevail and further grow by collecting dust from disassembled smaller bodies. The pile-up of solids in a confined inner region of the disc, in general, boosts the formation of planets. Erosion is possible in even strongly gas-depleted inner regions as observed for TW Hya. Reprocessing of dust through light-induced erosion offers one possible explanation for growth of large cores of gas-poor giant planets in a gas-starved region as recently found around HD 149026b.