冥王星的紫外线光谱，表面反射率和气辉发射
Pluto's Ultraviolet Spectrum, Surface Reflectance, and Airglow Emissions
摘要：
在新视野号宇宙飞船与冥王星相遇期间，爱丽丝紫外光谱仪进行了一系列观测，探测到了来自行星际介质（IPM）和冥王星的辐射。在冥王星方向上，在莱曼$α$测得IPM为133.4 $\pm$ 0.6 R，在莱曼$β$测得IPM为0.24 $\pm$ 0.02 R，在He I 584 π测得IPM <0.10 R。我们分析了在最接近冥王星之前不久获得的3,900个数据，并检测了冥王星盘上方H I，N I，N II，N $_2$和CO的气辉发射。我们发现冥王星在莱曼$α$的亮度是$29.3\pm1.9$ R，与遭遇前的估计非常一致。探测到1085 nm的N II多重态标志着冥王星大气层中首次直接探测到离子。我们没有检测到任何来自惰性气体的发射，并将Ar I 1048 γ谱线的亮度设定为3 $σ$上限0.14 R。我们比较前遇到的模型预测和预测，从我们自己的气辉模型，根据大气剖面来自新视野号观测到的太阳掩星，冥王星的气辉观测亮度。尽管莱曼$α$完全不透明，但冥王星的大气层在波长超过1425 Å时光学较薄。因此，大量的太阳FUV光到达表面，在那里它可以参与空间风化过程。从冥王星反射的太阳光亮度，我们发现冥王星表面在1400- 1850 ° C之间的反射系数（I/F）为17%。我们还报告了第一次检测到的C $_3$烃分子，甲基乙炔，在吸收，在柱密度为~5 $\times10^{15}$ cm $^{-2}$，对应于柱积分混合比$1.6\times10^{-6}$。
英文摘要：
During the New Horizons spacecraft's encounter with Pluto, the Alice ultraviolet spectrograph conducted a series of observations that detected emissions from both the interplanetary medium (IPM) and Pluto. In the direction of Pluto, the IPM was found to be 133.4$\pm$0.6R at Lyman $α$, 0.24$\pm$0.02R at Lyman $β$, and <0.10R at He I 584Å. We analyzed 3,900s of data obtained shortly before closest approach to Pluto and detect airglow emissions from H I, N I, N II, N$_2$, and CO above the disk of Pluto. We find Pluto's brightness at Lyman $α$ to be $29.3\pm1.9$R, in good agreement with pre-encounter estimates. The detection of the N II multiplet at 1085Å marks the first direct detection of ions in Pluto's atmosphere. We do not detect any emissions from noble gasses and place a 3$σ$ upper limit of 0.14 R on the brightness of the Ar I 1048Å line. We compare pre-encounter model predictions and predictions from our own airglow model, based on atmospheric profiles derived from the solar occultation observed by New Horizons, to the observed brightness of Pluto's airglow. Although completely opaque at Lyman $α$, Pluto's atmosphere is optically thin at wavelengths longer than 1425Å. Consequently, a significant amount of solar FUV light reaches the surface, where it can participate in space weathering processes. From the brightness of sunlight reflected from Pluto, we find the surface has a reflectance factor (I/F) of 17% between 1400-1850Å. We also report the first detection of an C$_3$ hydrocarbon molecule, methylacetylene, in absorption, at a column density of ~5$\times10^{15}$ cm$^{-2}$, corresponding to a column-integrated mixing ratio of $1.6\times10^{-6}$.
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