米级地球撞击体的大气层前探测
Preatmospheric detection of a meter-sized Earth impactor
AI总结：
本文报告了2020年一颗3米直径流星体撞击地球前10分钟的望远镜探测，结合多传感器数据确认其为自然C-复合型近地小行星，这是迄今撞击前最近距离的初始望远镜探测。
摘要：
2020年9月18日，美国政府传感器在西太平洋上空探测到一个峰值热星等为-19的火流星。此次撞击也被GOES-17卫星上的静止闪电测绘仪（GLM）和夏威夷的次声传感器探测到。USG测量报告称，其进入角相对于水平面陡峭，为67°，辐射点位于北偏东13°，撞击速度为11.7 km s$^{-1}$。对所有能量产额的解释得出首选能量估计为0.4 kt TNT，对应一颗23000千克、直径3米的流星体。撞击后的望远镜图像搜索发现，ATLAS巡天在撞击前仅10分钟、地心距离近11900公里处捕捉到了该天体，其视星等为m=12.5。该天体表现为一条0.44°的条纹，起始于图像东边缘，在30秒曝光时间内延伸了基于USG状态向量预测的1.26°的三分之一。条纹显示出与小型小行星自转一致的亮度变化。地球阴影的位置、该天体的大小及其与报告的USG状态向量的一致性，证实该天体很可能是自然天体。这是近地小行星（NEA）撞击体的第八次大气层前探测，也是撞击前最近距离的初始望远镜探测。火流星峰值亮度的高海拔特征表明它是一个脆弱的天体，在许多方面与2008 TC3（Almahata Sitta陨石）相当，其绝对星等H=32.5且反照率可能较低。因此，我们认为该NEA是一颗C-复合型小行星。
英文摘要：
On 2020 September 18 US Government sensors detected a bolide with peak bolometric magnitude of -19 over the western Pacific. The impact was also detected by the Geostationary Lightning Mapper (GLM) instrument on the GOES-17 satellite and infrasound sensors in Hawaii. The USG measurements reported a steep entry angle of $67^{\circ}$ from horizontal from a radiant $13^{\circ}$ E of N and an impact speed of 11.7 km s$^{-1}$. Interpretation of all energy yields produces a preferred energy estimate of 0.4 kt TNT, corresponding to a $23000$ kilogram $3$ meter diameter meteoroid. A post-impact search of telescopic images found that the ATLAS survey captured the object just 10 minutes prior to impact at an Earth-centred distance of nearly $11900$ kilometers with apparent magnitude $m\text{=}12.5$. The object appears as a $0.44^{\circ}$ streak originating on the eastern edge of the image extending one-third of the USG state vector-based prediction of $1.26^{\circ}$ over the 30 second exposure. The streak shows brightness variability consistent with small asteroid rotation. The position of Earth's shadow, the object's size, and its consistency with the reported USG state vector confirm the object is likely natural. This is the eighth preatmospheric detection of a Near-Earth Asteroid (NEA) impactor and the closest initial telescopic detection prior to impact. The high altitude of peak fireball brightness suggest it was a weak object comparable in many respects with 2008 TC3 (Almahata Sitta meteorite), with absolute magnitude $H=32.5$ and likely low albedo. Therefore we suggest the NEA was a C-complex asteroid.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
