The composition and origin of the C, P, and D asteroids: Water as a tracer of thermal evolution in the outer belt
The composition and origin of the C, P, and D asteroids: Water as a tracer of thermal evolution in the outer belt
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C、P 和 D 小行星的组成和起源：水作为外带热演化的示踪剂
DOI：
10.1016/0019-1035(90)90184-b
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发表时间：
1990
期刊：
影响因子：
3.2
通讯作者：
M. Marley
中科院分区：
文献类型：
--
作者：
T. Jones;L. Lebofsky;JOHN S. Lewis;M. Marley
我们介绍了对低反照率外带小行星(2.5-5.2AU)中H2O分布的广泛实验室和望远镜研究结果。水的分布是通过测量该地区小行星分子H2O和结构羟基离子的3-ωm反射吸收来确定的，3-ωm波段是陨石和小行星水化硅酸盐的光谱特征。调查中观测到的19颗小行星，加上早先的反射率数据，产生了3-ωm波段深度测量，反映了目前外带H2O的分布。在这个样本中的32颗C级小行星中，66%的小行星表面有水化的硅酸盐，这是太阳系历史早期轻微的水蚀变事件的证据。C类不是矿物学意义上的原始小行星群，但它的无水成分似乎变化很小，超过3.5AU的P和D类也是如此。除了Cs与更远的P_s和D之间明显的水化状态差异外，Cs中的水化硅酸盐丰度在2.5-3.5AU之间逐渐下降。再加上表面上无水的P和D表面，这指向了原始的外带小行星组成，由无水硅酸盐、水冰和复杂的有机物质组成。早期太阳风对原小行星的感应加热强度随着日心距离的增加而减弱，并导致观测到的水合硅酸盐丰度径向下降。外带小行星的温和热过程是2.5AU向南强烈加热和分异的延续，这两个事件都符合感应加热机制。水冰可以保存在P和D物体的内部，以及一些较大的Cs中。
We present results of an extensive laboratory and telescopic investigation of H2O distribution among the low-albedo, outer belt asteroids (2.5–5.2 AU). The water distribution was determined by surveying asteroids in that region for the 3-ωm reflectance absorption of molecular H2O and structural OH ions; the 3-ωm band is the spectral signature of meteorite and asteroid hydrated silicates. The 19 asteroids observed in the survey, augmented by earlier reflectance data, yielded 3-ωm band depth measurements that reflect the present outer belt H2O distribution. Of the 32 C-class asteroids in this sample, 66% have hydrated silicate surfaces, evidence of a mild aqueous alteration episode early in solar system history. The C class is not a primitive asteroid group in the mineralogical sense, but its anhydrous members appear little altered, as do the P and D classes beyond 3.5 AU. In addition to this pronounced hydration state difference between Cs and the more distant Ps and Ds, hydrated silicate abundance declines gradually among the Cs from 2.5–3.5 AU. Coupled with the apparently anhydrous P and D surfaces, this points to an original outer belt asteroid composition of anhydrous silicates, water ice, and complex organic material. Early solar wind induction heating of proto-asteroids declined in intensity with heliocentric distance, and produced the observed radial decrease in hydrated silicate abundance. The mild thermal processing of outer belt asteroids is a continuation of the intense heating and differentiation that occurred sunward of 2.5 AU, and both events are consistent with the induction heating mechanism. Water ice may be preserved in the interiors of P and D objects, and in some larger Cs.