发表机构
Northern Arizona University（北亚利桑那大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究量化冰相和辐射对4.14 μm HDO吸收带的影响，发现无定形冰和辐射处理会削弱该特征，导致D/H比低估，但可通过晶体部分估算修正。
AI 中文摘要
确定外星物体表面的同位素比率可以深入了解其形成条件和演化过程。最近，对4.14 μm HDO吸收带的遥感探测使天文学家能够估算外太阳系中多个冰体的D/H比。在此，我们量化了冰相和辐射处理对4.14 μm吸收带的影响。虽然该波段在含有晶体成分的H2O冰样品中可见，但在无定形H2O冰中我们无法检测到它。此外，我们发现，以10 keV电子作为代理的辐射处理，会迅速使该吸收特征变得不可检测，其速率与初始晶体样品的无定形化一致。有趣的是，我们还发现，对辐照样品进行再结晶会使该波段几乎恢复到其原始波段深度。对于土星卫星土卫一（Mimas），我们估计，在遥感光谱探测的典型深度下，HDO特征将在约1 x 10^4年内减少一半。虽然我们怀疑现有方法仍可从完全由晶体H2O冰组成的表面确定D/H比，但对于具有显著无定形部分的表面，推导D/H比可能导致对真实D/H比的严重低估。然而，鉴于样品的无定形部分与HDO波段深度之间的直接相关性，我们提出，通过使用其他吸收特征确定表面H2O冰的晶体部分，仍可估计具有混合相表面的D/H比。
英文摘要
Determining isotopic ratios on the surfaces of extraterrestrial objects can provide insight into their formation conditions and evolution. Recently, remote-sensing detections of the 4.14 μm HDO absorption band have enabled astronomers to estimate the D/H ratio on several icy objects in the outer solar system. Here, we quantify how ice phase and radiation processing affect the 4.14 μm absorption band. While the band is visible in H2O-ice samples with a crystalline component, we cannot detect it in amorphous H2O-ice. Furthermore, we find that radiation processing, using 10 keV electrons as a proxy, quickly makes this absorption feature undetectable at a rate consistent with the amorphization of an initially crystalline sample. Interestingly, we also find that recrystallizing the irradiated sample causes this band to reappear nearly to its original band depth. For the Saturnian satellite Mimas, we estimate that the HDO feature will decrease by a factor of two within ~1 x 10^4 yrs at typical depths probed by remote sensing spectroscopy. While we suspect that existing methods could still determine the D/H ratio from a surface composed entirely of crystalline H2O-ice, deriving it for surfaces with a significant amorphous fraction may lead to severe underestimation of the true D/H ratio. However, given the direct correlation between the amorphous fraction of the sample and the HDO band depth, we propose that one could still estimate the D/H ratio of a surface with mixed phases by determining the crystalline fraction of the surface H2O-ice using other absorption features.
Comments14 pages; 5 figures
