论文标题
在1.0-1.8 $μm$的空间解决欧罗巴表面的空间分辨观察结果：上限的上限
Spatially resolved observations of Europa's surface with Subaru/IRCS at 1.0-1.8 $μm$: Upper limits to the abundances of hydrated Cl-bearing salts
论文作者
论文摘要
最近，使用大型地面望远镜的红外线观测值为1.5-4.0 $μm$，这表明含Cl的盐可能以欧罗巴的表面作为非冰材料存在。那些含Cl的盐的化学成分是了解欧罗巴的海洋化学和可居住性的关键。在这里，我们报告了在两个波长范围1.0-1.5和1.5-1.8 $μm$的欧罗巴望远镜观察结果的结果，其中前一个范围包括一些由于一些水合的CLEARGEANT盐而吸收特征。我们使用Subaru望远镜/IRC和具有高波长分辨率的自适应光学系统AO188获得了空间分辨的反射光谱（$Δλ$ 〜2 nm for 1.0-1.5 $ $ $ $ $ $和$Δλ$和$δλ$ 〜0.9 nm，对于1.5-1.8 $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ 〜6 $ 〜6 $ 〜σ 10 $^{ - 3} $）。我们发现，没有水合CL的盐引起的〜1.2 $ $ m的清晰吸收特征。我们估计，保守的上限是MGCL $ _2 $ _2 $ \ CDOT $ NH $ _2 $ O，NACLO $ _4 $ _4 $ _4 $ \ CDOT $ 2H $ _2 $ o，mg（clo $ _3 $ _ 2 $ _ 2 $ _ 2 $ _ 2 $ 6H $ _2 $ _2 $ o，和毫克（Clo $ _4 $）$ _ 2 $$ \ CDOT $ 6H $ _2 $ o o y on Europa上的17％（大多数<10％）在3 $σ$噪声水平上。这些值低于基于先前的观察结果，欧罗巴上某些水合Cl的盐（>约20％）的拟议丰度。这支持了这样一个想法，即欧罗巴上的含Cl的盐可能是NaCl和/或Naclo $ _4 $的无水Na盐，或水合的NACL $ \ cdot $ 2H $ _2 $ o。 NA盐的存在表明Na $^+$可能是欧罗巴海洋中的主要阳离子，如果海洋pH是环中或碱性的，则可能是可能的。
Recent infrared observations at 1.5-4.0 $μm$ using large ground-based telescopes have suggested that Cl-bearing salts are likely present on Europa's surface as non-ice materials. The chemical compositions of those Cl-bearing salts are key to understanding Europa's ocean chemistry and habitability. Here we report the results of ground-based telescope observations of Europa across two wavelength ranges, 1.0-1.5 and 1.5-1.8 $μm$, of which the former range includes absorption features owing to some hydrated Cl-bearing salts. We obtained spatially resolved reflectance spectra using the Subaru Telescope/IRCS and the adaptive optics system AO188 with high wavelength resolutions ($δλ$ ~ 2 nm for 1.0-1.5 $μm$ and $δλ$ ~ 0.9 nm for 1.5-1.8 $μm$) and low noise levels (1$σ$ ~ 1-2 $\times$ 10$^{-3}$). We found no clear absorption features at ~1.2 $μ$m caused by hydrated Cl-bearing salts. We estimated that conservative upper limits to the abundances of MgCl$_2$$\cdot$nH$_2$O, NaClO$_4$$\cdot$2H$_2$O, Mg(ClO$_3$)$_2$$\cdot$6H$_2$O, and Mg(ClO$_4$)$_2$$\cdot$6H$_2$O on Europa are 17% (<10% for most) at the 3$σ$ noise level. These values are lower than the proposed abundance of some hydrated Cl-bearing salts (> ~20%) on Europa based on previous observations. This supports the idea that Cl-bearing salts on Europa are likely anhydrous Na salts of NaCl and/or NaClO$_4$, or hydrated NaCl$\cdot$2H$_2$O. The presence of Na salts suggests that Na$^+$ could be the major cation in Europa's ocean, which would be possible if the oceanic pH is circumneutral or alkaline.
