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
