Photophoretic transport of hot minerals in the solar nebula

Abstract

Context. 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. Aims. 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. Methods. 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 −1 m) and density (500 and 1000 kg m −3 ). 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. Results. Depending on the postulated disk parameters and the density of particles, 10 −2 to 10 −1 m aggregates can reach heliocentric distances up to ∼35 AU in the primordial nebula over very short timescales (no more than a few hundred thousand years). 10 −3 m particles follow the same trajectory as the larger ones but their maximum migration distance does not exceed ∼26 AU and is reached at later epochs in the disks. On the other hand, 10 −5 to 10 −4 m 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. Conclusions. 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.

Inner dusty regions of protoplanetary discs - I. High-resolution temperature structure

“…This leads to the coupling of grain settling to the distribution of the magnetorotational turbulence (Turner et al 2010). High gas densities also provide conditions for photophoresis on large grains, which moves particles outward (Moudens et al 2011). Moreover, these dynamical processes could vary optical depth within R in , which would immediately influence the optically thick region where the dust at the sublimation zone can overheat and sublimate.…”

Photophoresis of dust aggregates in protoplanetary disks

“…λ/J 1 ≈ 0.001 W/(mK), we expect that their results will change quantitatively but not qualitatively: particle transport will be slower and less efficient by up to two orders of magnitude. The calculated time-dependent equilibrium distances for dust aggregates of a given size will be further inward than estimated by Moudens et al (2011) The dependence of the strength of the photophoretic effect on the material properties has nevertheless implications on the visible chemical distribution of elements within the disk. This is especially true for the photophoretic effect of dust aggregates by the infrared radiation of the disk itself (Wurm et al 2010), which allows for particles to be levitated above the dust sub-disk, due to the disk's infrared emission.…”

“…(4) with the assumption that the first term in the denominator dominates over the other two, one of our results is that for dust aggregates in the sub-mm size regime, the value λ/J 1 ≈ 0.1 W/(mK). Comparing these values for the ratio of the dust-aggregates' heat conductivity and the asymmetry factor with the assumptions of Moudens et al (2011), i.e. λ/J 1 ≈ 0.001 W/(mK), we expect that their results will change quantitatively but not qualitatively: particle transport will be slower and less efficient by up to two orders of magnitude.…”

“…2 assume a steady-state disk of the minimum mass solar nebula with an optically thin inner gap in the disk according to the distance given in the abscissa. Moudens et al (2011) carried out a detailed theoretical analysis of particle motion within an evolving disk, taking into account gas density, opacity changes and turbulence which result in different equilibrium radial positions of particles of different sizes. Thus, a the size dependence of the velocities at a given radial position cannot be easily inferred so that a comparison of their velocities to ours is not possible, albeit photophoretic velocities are in the expected range.…”

From Planetesimals to Dust: Low-Gravity Experiments on Recycling Solids at the Inner Edges of Protoplanetary Disks

“…Such a model has been suggested by Wurm & Haack (2009). At later times or throughout the optically thin inner parts the dust might also be transported by photophoresis in the midplane (Wurm 2007;Takeuchi & Lin 2003;Herrmann & Krivov 2007;Moudens et al 2011;Mousis et al 2007). showed that the erosion process is a suitable mechanism to explain the existence of small dust particles which are observed in protoplanetary disks over their entire lifetime.…”