标题： 使用哈勃太空望远镜/空间望远镜成像光谱仪对木卫四的光谱测绘及其表面成分的启示 显示英文标题

标题： Spectroscopic Mapping of Callisto with HST/STIS and Implications for its Surface Composition

摘要： 我们展示了利用哈勃太空望远镜空间望远镜成像光谱仪（HST/STIS）获得的木卫四全球、空间分辨的紫外-可见光谱，并探索了木卫四表面物质可能的组成。 我们绘制了从700到1000纳米波段内近紫外和近红外光谱斜率的广泛下降强度图，该强度从略微偏蓝（700到1000纳米波段反射率递减）到红色（反射率递增）变化，覆盖了木卫四整个表面。 在全球范围内，明亮且富含水冰的区域倾向于具有中性或蓝色的近红外光谱斜率以及较浅的近紫外下降，而较暗的材料则与红色近红外光谱斜率和更强的近紫外吸收相关联。 在820和930纳米附近的宽吸收带与阿斯加德和瓦尔哈拉撞击盆地的空间位置相关，可能与含铁硅酸盐有关。 在275纳米附近的吸收边缘主要映射到木卫四的后随半球，而在320纳米处的吸收主要出现在阿斯加德和瓦尔哈拉及其周围区域，可能与有机物有关。 我们在230和450纳米附近报告了两个新的吸收特征，可能归因于辐射照射的NaCl。 我们在紫外-可见波长范围内几乎没有发现含硫物种的证据，并建议在前导/拖尾半球比值光谱中仅看到的280纳米带先前被归因于SO2，但更可能是由于将无关的320纳米前导半球带除以拖尾半球的275纳米吸收边缘的结果。 光谱特征的空间变化表明，木卫四的暗色物质成分在地区间有所不同，反映了内源性和外源性来源以及辐射分解改造的混合影响。 显示英文摘要

摘要： We present global, spatially resolved ultraviolet-visible spectra of Callisto obtained with HST/STIS and explore possible compositions of Callisto's surface material. We map the strength of a widespread downturn toward the near-UV and the NIR spectral slope from 700 to 1000 nm, which varies from slightly blue (reflectance decreasing from 700 to 1000 nm) to red (reflectance increasing) across Callisto's surface. Globally, bright water-ice-rich regions tend to have neutral or blue NIR slopes and a shallower near-UV downturn, while darker material is associated with red NIR slopes and stronger near-UV absorption. Broad absorptions near 820 and 930 nm are spatially correlated with the Asgard and Valhalla impact basins and may be associated with iron-bearing silicates. An absorption edge near 275 nm maps primarily to Callisto's trailing hemisphere, and a 320 nm absorption most prevalent within and surrounding Asgard and Valhalla may be related to organics. We report two new absorption features near 230 and 450 nm which might be attributed to irradiated NaCl. We find little evidence for sulfur-bearing species at UV-visible wavelengths and suggest that a 280 nm band seen only in leading/trailing hemisphere ratio spectra and previously attributed to SO2 is better explained as a consequence of dividing the unrelated 320 nm leading hemisphere band by the trailing hemisphere 275 nm absorption edge. Spatial variations in spectral features suggest that Callisto's dark material composition varies regionally, reflecting a mix of endogenic and exogenic sources and radiolytic alteration.