Experimental study on the chemical strucutre of the Jovian planets and their satellistes

为了了解类木行星冰态卫星的化学结构，我们利用金刚石砧细胞研究了高达10 GPa的h2o - nh_3体系的相关系。起始原料为含氨量高达26.8 wt%的氨水溶液。通过高压下的显微观察来确定相关系，通过高压下的原位x射线衍射来确定相。在H_2O-14wt%NH_3组分（由H_2O和NH_3的宇宙比组成）中，液相压力在295 K时为1.2 Gpa，此时冰VI开始结晶为液相相。固相位于2gpa和295gpa之间，在这里Ice VI和氨水合物是稳定的。在295 K下，水合物氨在4 GPa左右转变为未知相。由于缺乏x射线衍射数据的质量，未知氨水合物的结构尚未确定。根据目前的研究结果，冰冻卫星内部的温度分布以及冰的多晶态与氨水溶液的密度关系，认为卫星内部部分熔融形成的富氨液体有向上移动和向空间分散的趋势。因此，高挥发性成分，如NH_3，可能会在目前的类木行星的冰卫星中耗尽。

We have studied the phase relation of H_2O-NH_3 system up to 10 GPa by using the diamond anvil cell, in order to understand the chemical structure of icy satellites of the Jovian Planets. The starting materials were the aqueous ammonia solutions containing ammonia up to 26.8 wt%. Determination of the phase relations was conducted by microscopic observation of the sample at high pressure, while identification of the phases was made by in situ X-ray diffraction at high pressure.The pressure of the liquidus in the H_2O-14wt%NH_3 composition, which is the composition of the cosmic ratio of H_2O and NH_3, was 1.2 Gpa at 295 K, where Ice VI begins to crystallize as the liquidus phase. The solidus locates at around 2 GPa at 295 GPa, where Ice VI and an ammonia hydrate are stable. The ammonia hydrate seems to transform into unknown phase at around 4 GPa at 295 K. The structures of the unknown ammonia hydrates are not identified due to lack of quality of the X-ray diffraction data.On the basis of the present results, the estimated temperature distributions in the icy satellites, and the density relationship between polymorphs of ice and the aqueous ammonia solution, it is suggested that the ammonia enriched liquid formed by partial melting in the interior of the satellites tends to move upwards and to disperse into the space. Thus highly volatile components such as NH_3 could be depleted in the present icy satellites of the Jovian Planets.