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arXiv 2004.00625astro-ph.EPastro-ph.IM
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小行星碰撞引起的普通球粒陨石激波变暗的实验限制

Experimental constraints on the ordinary chondrite shock darkening caused by asteroid collisions

T. Kohout, E. V. Petrova, G. A. Yakovlev, V. I. Grokhovsky, A. Penttilä, A. Maturilli, J. -G. Moreau, S. V. Berzin, J. Wasiljeff, I. A. Danilenko, D. A. Zamyati… 展开作者

T. Kohout, E. V. Petrova, G. A. Yakovlev, V. I. Grokhovsky, A. Penttilä, A. Maturilli, J. -G. Moreau, S. V. Berzin, J. Wasiljeff, I. A. Danilenko, D. A. Zamyatin, R. F. Muftakhetdinova, M. Heikkilä

摘要:

已知与撞击或行星碰撞有关的普通球粒陨石中的冲击引起的变化能够改变其光学特性。因此,我们可以假设,普通球粒陨石物质的很大一部分可能隐藏在观测到的暗C/X小行星群中。冲击波致暗化的精确压力-温度条件没有很好的约束。因此,我们实验研究的球粒陨石材料的光学性质的冲击压力的函数的逐渐变化。用车里雅宾斯克LL 5进行了球形激波实验,以研究其光学性质的变化。球形激波实验的几何形状允许激波压力从边缘处的$\sim$ 15 GPa逐渐增加到中心处的数百吉帕斯卡。随着冲击载荷的增加,观察到四个不同的区域。在高达$\sim$ 50 GPa时,光学变化最小。在$\sim$ 50- 60 GPa范围内,由于陨硫铁熔体注入硅酸盐中,发生了冲击变暗。由于硅酸盐开始熔化,该过程在$\sim$ 60 GPa的压力下突然停止。在高于$\sim$ 150 GPa的压力下,发生再结晶,并与第二阶段冲击变暗有关,这是由于细的铁镍合金-金属共晶晶粒。冲击波暗化影响紫外、可见和近红外(UV、VIS和NIR)区域,而对MIR光谱的变化很小。激波暗化是由两种具有特征压力区的不同机制引起的,这两个压力区被暗化停止的间隔所分隔。这意味着在小行星碰撞过程中产生的冲击变暗物质的数量减少。

英文摘要:

Shock-induced changes in ordinary chondrite meteorites related to impacts or planetary collisions are known to be capable of altering their optical properties. Thus, one can hypothesize that a significant portion of the ordinary chondrite material may be hidden within the observed dark C/X asteroid population. The exact pressure-temperature conditions of the shock-induced darkening are not well constrained. Thus, we experimentally investigate the gradual changes in the chondrite material optical properties as a function of the shock pressure. A spherical shock experiment with Chelyabinsk LL5 was performed in order to study the changes in its optical properties. The spherical shock experiment geometry allows for a gradual increase of shock pressure from $\sim$15 GPa at a rim toward hundreds of gigapascals in the center. Four distinct zones were observed with an increasing shock load. The optical changes are minimal up to $\sim$50 GPa. In the region of $\sim$50--60 GPa, shock darkening occurs due to the troilite melt infusion into silicates. This process abruptly ceases at pressures of $\sim$60 GPa due to an onset of silicate melting. At pressures higher than $\sim$150 GPa, recrystallization occurs and is associated with a second-stage shock darkening due to fine troilite-metal eutectic grains. The shock darkening affects the ultraviolet, visible, and near-infrared (UV, VIS, and NIR) region while changes to the MIR spectrum are minimal. Shock darkening is caused by two distinct mechanisms with characteristic pressure regions, which are separated by an interval where the darkening ceases. This implies a reduced amount of shock-darkened material produced during the asteroid collisions.

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