We analyzed spectral cubes of Callisto’s leading and trailing hemispheres, collected with the NIRSpec Integrated Field Unit (G395H) on the James Webb Space Telescope. These spatially resolved data show strong 4.25 μm absorption bands resulting from solid-state ¹²CO₂, with the strongest spectral features at low latitudes near the center of its trailing hemisphere, consistent with radiolytic production spurred by magnetospheric plasma interacting with native H₂O mixed with carbonaceous compounds. We detected CO₂ rovibrational emission lines between 4.2 and 4.3 μm over both hemispheres, confirming the global presence of CO₂ gas in Callisto’s tenuous atmosphere. These results represent the first detection of CO₂ gas over Callisto’s trailing side. The distribution of CO₂ gas is offset from the subsolar region on either hemisphere, suggesting that sputtering, radiolysis, and geologic processes help sustain Callisto’s atmosphere. We detected a 4.38 μm absorption band that likely results from solid-state ¹³CO₂. A prominent 4.57 μm absorption band that might result from CN-bearing organics is present and significantly stronger on Callisto’s leading hemisphere, unlike ¹²CO₂, suggesting these two spectral features are spatially antiassociated. The distribution of the 4.57 μm band is more consistent with a native origin and/or accumulation of dust from Jupiter’s irregular satellites. Other, more subtle absorption features could result from CH-bearing organics, CO, carbonyl sulfide, and Na-bearing minerals. These results highlight the need for preparatory laboratory work and improved surface–atmosphere interaction models to better understand carbon chemistry on the icy Galilean moons before the arrival of NASA’s Europa Clipper and ESA’s JUICE spacecraft.

中文翻译：

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通过 JWST 揭示木卫四富含碳的表面和二氧化碳大气

我们分析了木卫四前半球和后半球的光谱立方体，这些立方体是用詹姆斯·韦伯太空望远镜上的 NIRSpec 综合现场装置 (G395H) 收集的。这些空间分辨数据显示出很强的 4.25μm 吸收带由固态¹² CO ₂产生，在其尾随半球中心附近的低纬度地区具有最强的光谱特征，这与磁层等离子体与与碳质化合物混合的天然 H ₂ O 相互作用刺激的辐射分解产生一致。我们检测到 CO ₂旋转发射线在 4.2 和 4.3 之间μ米在两个半球上空，证实了木卫四稀薄大气中全球范围内存在CO ₂气体。这些结果代表了首次在木卫四尾随侧检测到 CO _{2气体。 CO 2}气体的分布与两个半球的太阳下区域有所偏移，这表明溅射、辐射分解和地质过程有助于维持木卫四的大气层。我们检测到 4.38μm 吸收带可能由固态¹³ CO ₂产生。突出的4.57μ^与12 CO ₂不同，木卫四主半球上存在可能由含 CN 有机物产生的 m 吸收带，并且明显更强，这表明这两个光谱特征在空间上是反关联的。 4.57 的分布μm波段更符合木星不规则卫星的原生起源和/或尘埃积累。其他更微妙的吸收特征可能是由含 CH 有机物、CO、硫化羰和含 Na 矿物产生的。这些结果凸显了在美国宇航局欧罗巴快艇和欧空局 JUICE 航天器抵达之前，需要进行实验室准备工作和改进表面-大气相互作用模型，以便更好地了解冰冷的伽利略卫星上的碳化学。