A ground-based observation of the LCROSS impact events using the Subaru Telescope
A ground-based observation of the LCROSS impact events using the Subaru Telescope
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使用斯巴鲁望远镜对 LCROSS 撞击事件进行地面观测
DOI：
10.1016/j.icarus.2011.05.008
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发表时间：
2011
期刊：
影响因子：
3.2
通讯作者：
Rei
中科院分区：
文献类型：
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作者：
Peng K.Hong;Seiji Sugita;Natsuko Okamura;Yasuhito Sekine;Hiroshi Terada;Naruhisa Takatoh;Yutaka Hayano;Tetsuharu Fuse;Tae-Soo Pyo;Hideyo Kawakita;Diane H.Wooden;Eliot F.Young;Paul G.Lucey;Kosuke Kurosawa;Hidenori Genda;Junichi Haruyama;Rei
月球陨石坑观测和遥感卫星(LCROSS)任务是一次撞击勘探，通过挖掘近地表物质在永久阴影区域(PSR)寻找挥发性矿藏。我们使用斯巴鲁望远镜对LCROSS撞击进行了从第一次碰撞前15分钟到第二次碰撞后2分钟的红外光谱和成像观测，以测量喷出的尘埃和水。这种地面观测很重要，因为观测几何和波长覆盖范围与LCROSS航天器非常不同。我们使用光谱分辨率为λ/Δλ∼~10,000的Echelle光谱仪观测了2.9 m附近的非共振H2O旋转发射线，并使用带有AK滤光片的狭缝观察器对喷出的羽流进行了成像观测。使用均匀弹丸进行的撞击前计算预测，分别有2000千克的喷射物和10千克的水被挖掘并扔进紧邻Thek成像仪视场(FOV)和光谱仪狭缝的视场(FOV)内狭缝上方的分析区域。然而，没有检测到明确的H2O或粉尘发射线。对于成像器视野内和狭缝视野内分析区域的3σ噪声，主要半人马撞击产生的尘埃和H2O的估计上限分别为800亿公斤和40亿公斤。如果以1σ为检测限，上限分别为300千克和14千克。尽管水质量的上限与标准理论预测的结果相当，但尘埃质量的上限明显小于标准撞击理论的预测。抛射尘埃质量的理论预测与我们的观测结果之间的差异表明，LCROSS撞击引起的陨石坑过程可能与标准陨石坑理论有很大不同，可能是因为它是中空的弹丸结构。
The Lunar Crater Observation and Sensing Satellite (LCROSS) mission was an impact exploration searching for a volatile deposit in a permanently shadowed region (PSR) by excavating near-surface material. We conducted infrared spectral and imaging observations of the LCROSS impacts from 15 min before the first collision through 2 min after the second collision using the Subaru Telescope in order to measure ejecta dust and water. Such a ground-based observation is important because the viewing geometry and wavelength coverage are very different from the LCROSS spacecraft. We used the Echelle spectrograph with spectral resolutionλ/Δλ∼ 10,000 to observe the non-resonant H2O rotational emission lines near 2.9 μm and the slit viewer with aK′ filter for imaging observation of ejecta plumes. Pre-impact calculations using a homogeneous projectile predicted that 2000 kg of ejecta and 10 kg of H2O were excavated and thrown into the analyzed area immediately above the slit within the field of view (FOV) of theK′ imager and the FOV of spectrometer slit, respectively. However, no unambiguous emission line of H2O or dust was detected. The estimated upper limits of the amount of dust and H2O from the main Centaur impact were 800 kg and 40 kg for the 3σof noise in the analyzed area within the imager FOV and in the slit FOV, respectively. If we take 1σas detection limit, the upper limits are 300 kg and 14 kg, respectively. Although the upper limit for water mass is comparable to a prediction by a standard theoretical prediction, that for dust mass is significantly smaller than that predicted by a standard impact theory. This discrepancy in ejecta dust mass between a theoretical prediction and our observation result suggests that the cratering process induced by the LCROSS impacts may have been substantially different from the standard cratering theory, possibly because of its hollow projectile structure.