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arXiv 1611.05511astro-ph.EP
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作为球粒形成事件的星子碰撞

Planetesimal collisions as a chondrule forming event

Shigeru Wakita, Yuji Matsumoto, Shoichi Oshino, Yasuhiro Hasegawa

摘要:

球粒陨石含有独特的球形物质,称为球粒:亚毫米大小的硅酸盐颗粒,曾经在太阳星云的高温条件下熔化。我们用数值方法研究了球粒的形成过程之一--星子碰撞。先前的研究发现,当撞击速度超过2.5 km/s $^{-1}$时,通过原行星-小行星碰撞产生的撞击喷射会产生相当于撞击物质量1%的陨石球粒。根据陨石球粒的矿物学数据,未分化的星子比潜在分化的原行星更适合于形成陨石球粒的碰撞。我们使用激波物理代码研究了星子-星子碰撞,发现了两件事:一是星子-星子碰撞产生的球粒数量与原行星-星子碰撞几乎相同($\sim$ 1%)。另一种是当两个微行星相互碰撞时,产生的球粒数量随着碰撞速度的增加而增加。我们还发现,陨石球粒的祖先可以从更深的区域的大目标(微行星或原行星)比小的撞击物(微行星)。因此,目标的组成对于充分说明目前取样陨石球粒的矿物学数据十分重要。

英文摘要:

Chondritic meteorites contain unique spherical materials named chondrules: sub-mm sized silicate grains once melted in a high temperature condition in the solar nebula. We numerically explore one of chondrule forming processes, planetesimal collisions. Previous studies found that impact jetting via protoplanet-planetesimal collisions make chondrules with an amount of 1 % of impactors' mass, when impact velocity exceeds 2.5 km s$^{-1}$. Based on the mineralogical data of chondrules, undifferentiated planetesimals would be more suitable for chondrule-forming collisions than potentially differentiated protoplanets. We examine planetesimal-planetesimal collisions using a shock physics code and find two things: one is that planetesimal-planetesimal collisions produce the nearly same amount of chondrules as protoplanet-planetesimal collisions ($\sim$ 1 %). The other is that the amount of produced chondrules becomes larger as the impact velocity increases when two planetesimals collide with each other. We also find that progenitors of chondrules can be ejected from deeper regions of large targets (planetesimals or protoplanets) than small impactors (planetesimals). The composition of targets is therefore important to fully account for the mineralogical data of currently sampled chondrules.

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