Abstract
A planetesimal is an object of 1-10 km in size, from which planets in our solar system are formed. The formation process of the planetesimal is still controversial. Gravitational instability of a dust rich sublayer is a convincing model for the formation mechanism of the planetesimal, but it requires the ratio of dust to gas surface density enhanced by 5-20 times over normal cosmic values. Many models are proposed to enhance the ratio to trigger the gravitational instability; dust concentration by turbulence eddies, magnetohydrodynamic turbulence, radial drift of dust aggregates, anticyclonic vortices, and photoevaporation by UV rays. Here I show capillary instability followed by the sintering of H2O ice is an effective mechanism to increase the ratio locally. Fragments from the surface of the dust aggregate stagnate around the heliocentric distance where the sintering proceeds. This mechanism straightforwardly increases the dust to gas surface density ratio by a factor of 10 or more enough to trigger the gravitational instability.
