**Part 5**

**Special Topics on Simulations and Experimental Data** 

378 Hydrodynamics – Advanced Topics

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**0**

**16**

Hitoshi Miura

*Tohoku University*

*Japan*

*Graduate School of Science,*

**Hydrodynamics of a Droplet in Space**

It is considered that our solar system 4.6 billion years ago was composed of a proto-sun and the circum-sun gas disk. In the gas disk, originally micron-sized fine dust particles accumulated by mutual collisions to be 1000 km-sized objects like as planets. Therefore, to understand the planet formation, we have to know the evolution of the dust particles in the early solar gas disk. One of the key materials is a millimeter-sized and spherical-shaped grain

Chondrules are considered to have been formed from molten droplets about 4.6 billion years ago in the solar gas disk (Amelin et al., 2002; Amelin & Krot, 2007). Fig. 1 is a schematic of the formation process of chondrules. In the early solar gas disk, aggregation of the micron-sized dust particles took place before planet formation (Nakagawa et al., 1986). When the dust aggregates grew up to about 1 mm in size (precursor), some astrophysical process heated them to the melting point of about 1600 − 2100 K (Hewins & Radomsky, 1990). The molten dust aggregate became a sphere by the surface tension (droplet), and then cooled again to solidify in a short period of time (chondrule). The formation conditions of chondrules, such as heating duration, maximum temperature, cooling rate, and so forth, have been investigated experimentally by many authors (Blander et al., 1976; Fredriksson & Ringwood, 1963; Harold C. Connolly & Hewins, 1995; Jones & Lofgren, 1993; Lofgren & Russell, 1986; Nagashima et al., 2006; Nelson et al., 1972; Radomsky & Hewins, 1990; Srivastava et al., 2010; Tsuchiyama & Nagahara, 1981-12; Tsuchiyama et al., 1980; 2004; Tsukamoto et al., 1999). However, it has been controversial what kind of astronomical event could have produced chondrules in early solar system. The chondrule formation is one of the

The most plausible model for chondrule formation is a shock-wave heating model, which has been tested by many theoreticians (Ciesla & Hood, 2002; Ciesla et al., 2004; Desch & Jr., 2002; Hood, 1998; Hood & Horanyi, 1991; 1993; Iida et al., 2001; Miura & Nakamoto, 2006; Miura et al., 2002; Morris & Desch, 2010; Morris et al., 2009; Ruzmaikina & Ip, 1994; Wood, 1984). Fig. 2 is a schematic of dust heating mechanism by the shock-wave heating model. Initially, the chondrule precursors were floating in the gas disk without any large relative velocity against the ambient gas (panel (a)). When a shock wave was generated in the gas disk, the gas behind the shock front was accelerated suddenly. On the other hand, the chondrule

termed as "chondrule" observed in chondritic meteorites.

most serious unsolved problems in planetary science.

**1. Introduction**

**1.1 Droplet in space**

*Department of Earth Planetary Materials Science,*
