Thermal conductivity of porous aggregates

$\mathit{Context.}$ The thermal conductivity of highly porous dust aggregates is a key parameter for many subjects in planetary science; however, it is not yet fully understood. $\mathit{Aims.}$ In this study, we investigate the thermal conductivity of fluffy dust aggregates with filling factors of less than $10^{-1}$. $\mathit{Methods.}$ We determine the temperature structure and heat flux of the porous dust aggregates calculated by $N$-body simulations of static compression in the periodic boundary condition. $\mathit{Results.}$ We derive an empirical formula for the thermal conductivity through the solid network $k_{\rm sol}$ as a function of the filling factor of dust aggregates $\phi$. The results reveal that $k_{\rm sol}$ is approximately proportional to ${\phi}^{2}$, and the thermal conductivity through the solid network is significantly lower than previously assumed. In light of these findings, we must reconsider the thermal histories of small planetary bodies.Comment: 4 pages, 4 figures. Accepted for publication in Astronomy & Astrophysic

Thermal history of chondrules during shock-wave heating

Evaporation during chondrule melting may have resulted in depletion of volatile elements in chondrules. However, no evidence for a large degree of heavy-isotope enrichment has been reported in chondrules. In order to meet this observed constraint, the rapid heating rate at temperatures below the silicate solidus is required to form chondrules. We have developed a new shock-wave heating model with the radiative transfer among dust particles and calculated the thermal history of chondrules. We have found that optically-thin shock waves for the thermal continuum emission from dust particles can meet the high heating rate constraint, because the dust thermal emission does not keep the dust particles high temperature for a long time in the pre-shock region and dust particles are abruptly heated by the gas drag heating in the post-shock region. We have also found a trend that the optically-thick shock waves lead to rapid heating in the pre-shock region and rapid cooling in the post-shock region. On the contrary, the optically-thin shock waves have a tendency to cause slow heating in the pre-shock region and slow cooling in the post-shock region. Since these two tendencies seem to be inconsistent with observational constraints (rapid heating and slow cooling for chondrule formation), more careful quantitative studies are needed in the future to see if the shock-wave heating model can reproduce the observations

Formation of compound chondrules from supercooled melts

第6回極域科学シンポジウム[OA] 南極隕石11月16日（月）　国立国語研究所 2階 講