阋神星和鸟神星上甲烷冰中D/H和13C/12C比率的测量：内部活动的证据
Measurement of D/H and 13C/12C Ratios in Methane Ice on Eris and Makemake: Evidence for Internal Activity
AI总结：
詹姆斯·韦伯空间望远镜首次观测了阋神星和鸟神星甲烷冰重同位素体吸收带，测得的D/H和13C/12C比率表明其甲烷氢原子源自水，揭示了内部存在过去或现在的地球化学热活动。
摘要：
詹姆斯·韦伯空间望远镜的NIRSpec红外成像光谱仪在1至5微米的波长范围内，观测了反射阳光下的外太阳系矮行星阋神星和鸟神星。这两个天体都具有富含甲烷冰的高反照率表面，其纹理允许太阳光子在冰中经历长光程。有证据表明阋神星上4.2微米附近存在N2冰吸收，但鸟神星上没有。在4.67微米处，两个天体均未观察到CO冰吸收。首次在2.615微米（13CH4）、4.33微米（12CH3D）和4.57微米（12CH3D）处观测到甲烷两种重同位素体的吸收带。这些谱带使我们能够测量阋神星和鸟神星表面甲烷冰中的D/H比率分别为(2.5 +/- 0.5) x 10-4和(2.9 +/- 0.6) x 10-4，以及13C/12C比率分别为0.012 +/- 0.002和0.010 +/- 0.003。测得的D/H比率远低于彗星67P/Churyumov-Gerasimenko中假定原初甲烷的D/H比率，但与许多彗星和较大外太阳系天体水中D/H比率相似。这种相似性表明，阋神星和鸟神星上甲烷中的氢原子源自水，表明其内部深处过去甚至现在存在热环境中的地球化学过程。13C/12C比率与通常观测到的太阳系数值一致，表明没有出现13C的大量富集，如果它们表面目前的甲烷是大部分已逃逸到太空的更大储库的残留物，就会出现这种富集。可能的解释包括地质上近期来自内部的排气，以及循环表面甲烷储库以保持最表层焕然一新的过程。
英文摘要：
James Webb Space Telescope's NIRSpec infrared imaging spectrometer observed the outer solar system dwarf planets Eris and Makemake in reflected sunlight at wavelengths spanning 1 through 5 microns. Both objects have high albedo surfaces that are rich in methane ice, with a texture that permits long optical path lengths through the ice for solar photons. There is evidence for N2 ice absorption around 4.2 um on Eris, though not on Makemake. No CO ice absorption is seen at 4.67 um on either body. For the first time, absorption bands of two heavy isotopologues of methane are observed at 2.615 um (13CH4), 4.33 um (12CH3D), and 4.57 um (12CH3D). These bands enable us to measure D/H ratios of (2.5 +/- 0.5) x 10-4 and (2.9 +/- 0.6) x 10-4, along with 13C/12C ratios of 0.012 +/- 0.002 and 0.010 +/- 0.003 in the surface methane ices of Eris and Makemake, respectively. The measured D/H ratios are much lower than that of presumably primordial methane in comet 67P/Churyumov-Gerasimenko, but they are similar to D/H ratios in water in many comets and larger outer solar system objects. This similarity suggests that the hydrogen atoms in methane on Eris and Makemake originated from water, indicative of geochemical processes in past or even ongoing hot environments in their deep interiors. The 13C/12C ratios are consistent with commonly observed solar system values, suggesting no substantial enrichment in 13C as could happen if the methane currently on their surfaces was the residue of a much larger inventory that had mostly been lost to space. Possible explanations include geologically recent outgassing from the interiors as well as processes that cycle the surface methane inventory to keep the uppermost surfaces refreshed.
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