2011A&A...531A.106M

Hot temperature minerals have been detected in a large number of comets and were also identified in the samples of Comet Wild 2 that were returned by the Stardust mission. Meanwhile, observations of the distribution of hot minerals in young stellar systems suggest that these materials were produced in the inner part of the primordial nebula and have been transported outward in the formation zone of comets. We investigate the possibility that photophoresis provides a viable mechanism to transport high-temperature materials from the inner solar system to the regions in which the comets were forming. We use a grid of time-dependent disk models of the solar nebula to quantify the distance range at which hot minerals can be transported from the inner part of the disk toward its outer regions as a function of their size (10^–5 to 10^–1m) and density (500 and 1000 kg/m3). These models will also yield information on the disk properties (radius of the inner gap, initial mass, and lifetime of the disk). The particles considered here are in the form of aggregates that presumably were assembled from hot mineral individual grains ranging down to submicron sizes and formed by condensation within the hottest portion of the solar nebula. Our particle-transport model includes the photophoresis, radiation pressure, and gas drag. Depending on the postulated disk parameters and the density of particles, 10^–2 to 10^–1m aggregates can reach heliocentric distances up to ∼35AU in the primordial nebula over very short timescales (no more than a few hundred thousand years). 10^–3m particles follow the same trajectory as the larger ones but their maximum migration distance does not exceed ∼26AU and is reached at later epochs in the disks. On the other hand, 10^–5 to 10^–4m aggregates are continuously pushed outward during the evolution of the solar nebula. Depending on the adopted disk parameters, these particles can reach the outer edge of the nebula well before its dissipation. Our simulations suggest that irrespective of the employed solar nebula model, photophoresis is a mechanism that can explain the presence of hot temperature minerals in the formation region of comets. Comets probably had the time to trap the dust transported from the inner solar system either in their interior during accretion or in the form of shells surrounding their surface if they ended their growth before the particles reached their formation location.