Constraints on the Formation of Comets from D/H Ratios Measured in H2O and HCN
Constraints on the Formation of Comets from D/H Ratios Measured in H2O and HCN
复制标题
H2O 和 HCN 中测量的 D/H 比对彗星形成的限制
DOI：
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发表时间：
2000
期刊：
影响因子：
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通讯作者：
A. Drouart
中科院分区：
文献类型：
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作者：
O. Mousis;D. Gautier;D. Bockelée;F. Robert;B. Dubrulle;A. Drouart
这篇报告是A. Drouart et al. （1999, icarus140,129）论文的后续，该论文证明了太阳星云的适当模型允许我们根据LL3陨石和彗星中测量的原太阳D/H比来解释水中的氘富集。在本报告中，我们表明Drouart等人选择的模型也能够解释C/1995 O1彗星（Hale-Bopp）测量的HCN中的D/H。我们发现进入星云的HCN的D/H比为~ 4×10−3，这明显小于在冷暗云中测量到的值，但与在热分子核中发现的值一致。H2O和HCN冰从太阳前云落入星云盘状，在星云的湍流部分蒸发，与氢同位素交换，并与来自星云内部的水蒸气混合。随后，在海尔-波普彗星上测量到的D/H比为H2O和HCN的冰凝聚、凝聚并被纳入彗星的粒子中。根据这些结果，我们讨论了在来自奥尔特云的彗星中检测到的分子的故事。在海尔-波普彗星上发现的大多数分子都来自嵌在太阳系云中的冰。冰在进入星云或早期星云之前就蒸发了，随后又重新凝结，除了高度挥发的分子。根据A. Kouchi等人(1994,Astron。天体物理学。299,1009)，水冰凝结成晶体形式。我们讨论了最易挥发的物质以包合物水合物的形式被捕获的可能性。太阳外碳氮比和在彗星上观测到的太阳丰度中Ne/O的强烈耗竭与J. I. Lunine和D. J. Stevenson （1985, Astrophys）的笼形水合物理论一致。增刊。Ser.58, 493)。在柯伊伯带形成的彗星可能含有无定形的水冰，并保留了前太阳系云的同位素特征。新发表的天王星和海王星内部模型使我们能够计算出原天王星和原海王星水冰的D/H比与在彗星上测量到的结果一致。这证实了目前的假设，即形成天王星和海王星核心的彗星和星子具有相似的成分。
This report is the follow-up of the paper of A. Drouart et al. (1999, Icarus140, 129) in which it was demonstrated that appropriate models of the solar nebula permit us to interpret the deuterium enrichment in water with respect to the protosolar D/H ratio measured in LL3 meteorites and comets. In the present report, we show that the models selected by Drouart et al. are also able to explain D/H in HCN measured in Comet C/1995 O1 (Hale–Bopp). We find that the D/H ratio in HCN entering the nebula is ∼4×10−3, which is significantly less than values measured in cold dark clouds, but consistent with values found in hot molecular cores. Both H2O and HCN ices infalling from the presolar cloud onto the nebula discoid evaporated in the turbulent part of the nebula, isotopically exchanged with hydrogen, and mixed with water vapor coming from the inner part of the nebula. Subsequently, H2O and HCN ices with D/H ratios measured in Comet Hale–Bopp condensed, agglomerated and were incorporated in cometesimals. In the light of these results, we discuss the story of molecules detected in comets coming from Oort cloud. Most molecules detected in Comet Hale–Bopp originated from ices embedded in the presolar cloud. Ices vaporized prior to entering into the nebula or in the early nebula, and subsequently recondensed, except highly volatile molecules. According to A. Kouchi et al. (1994, Astron. Astrophys.290, 1009), water ice condensed in crystalline form. We discuss the possibility that the most volatile species were then trapped in the form of clathrate hydrates. The oversolar C/N ratio and the strong depletion of Ne/O with respect to the solar abundance observed in comets are in agreement with the theory of clathrate hydrates of J. I. Lunine and D. J. Stevenson (1985, Astrophys. suppl. Ser.58, 493). Comets formed in the Kuiper belt may contain amorphous water ice and have kept the isotopic signature of the presolar cloud. New published models of interiors of Uranus and Neptune permit us to calculate that the D/H ratios in proto-uranian and proto-neptunian water ices are in agreement with those measured in comets. This confirms the current assumption that cometesimals and planetesimals that formed the cores of Uranus and Neptune had similar compositions.