Kyoko K Tanaka

Space Utilization Research (January 16-17, 2017. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency(JAXA)(ISAS)), Sagamihara, Kanagawa Japan

Space Utilization Research (January 24-25, 2015. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency(JAXA)(ISAS)), Sagamihara, Kanagawa Japan

There are numerous amounts of nanoparticles, which have been called cosmic dust, in universe. Since cosmic dust is a building block of planetary system and works as a substrate for molecular formation, the estimation of their characters such as the composition, size and number density is very important subject in the field of planetary and astronomical sciences. Cosmic dust forms via homogeneous nucleation from ejecta gas of a dying star. To understand the formation condition, nucleation theory and homogeneous nucleation experiment is required. Recent our experiment under gravity indicated ...

We derived crystallization conditions of amorphous silicate by comparing theoretical model with three different kinds of crystallization experiments: annealing experiments of (1) an amorphous silicate with forsterite composition, (2) an amorphous silicate covered with a carbonaceous layer, and (3) an amorphous silicate covered with a carbonaceous layer consisting of reactive molecules (e.g., CH_4). From the experiments (1) and (2), we obtained the activation energies of diffusion in the amorphous silicate and amorphous carbon. From these values and the comparison with the experiment (3), we derived the constraints on the energy density stored in the mantle layer and the chemical reaction time to occur the crystallization of amorphous silicate.

We derived the interfacial energy of enstatite (MgSiO_3) by comparing the crystallization model with the number of nuclei measured in the experiment. Using the obtained value (430±50ergcm^<-2>), we calculated temperature evolutions for a variety of cooling rates of the enstatite liquid droplet. We found that the critical cooling rate for glass formation for enstatite melt is considerably low, i.e., 〜 10^<-7>K/s.

We carried out a numerical simulation of shock-wave heating event in early solar system. A shock wave heats and evaporates micron-sized silicate dust particles and generates a dust vapor. We found that the dust vapor cools to be supersaturated behind the shock front. The typical size and the morphology of condensates were discussed based on the classical nucleation theory.