近地小行星（52768）1998 OR2的物理特性：激波1变暗/撞击熔融的证据
Physical Characterization of Near-Earth Asteroid (52768) 1998 OR2: Evidence of Shock 1 Darkening/Impact Melt
摘要：
我们在2020年4月近距离接近地球期间对近地小行星（52768）1998 OR 2进行了光度和光谱表征。我们的测光测量确认小行星的旋转周期为4.126 +/- 0.179小时，与先前公布的4.112 +/- 0.001小时的值一致。通过结合我们的可见光谱测量（0.45 - 0.93微米）与档案MITHNEOS近红外光谱（0.78 - 2.49微米），我们将小行星分类为Bus-DeMeo分类中的Xn型。组合光谱显示两个弱吸收带：带I在0.926 +/- 0.003微米，带II在2.07 +/- 0.02微米，带深分别为4.5 +/- 0.15%和4.0 +/-0.21%。带面积比为1.13 +/-0.05。这些光谱带参数位于加菲S-小行星子类型图的S（IV）区域的尖端，表明与普通球粒陨石有亲和力。我们使用带I中心计算橄榄石和辉石的化学成分为20.1 +/- 2.3 mol%铁橄榄石和18.2 +/- 1.5 mol%硅铁石，与氢氧化镁石一致。对1998年OR 2的可见-近红外组合光谱的主成分分析落在α线的C/X复合物一侧，接近激波变暗趋势的末端，与其弱吸收带（带深< 5%）一致。我们使用一个空中混合模型与实验室测量的冲击变暗的H5球粒陨石，Chergach，以限制在小行星的表面上的冲击变暗的材料的量在~63%的黑暗岩性和~37%的轻岩性。
英文摘要：
We conducted photometric and spectroscopic characterization of near-Earth asteroid (52768) 1998 OR2 during a close approach to the Earth in April of 2020. Our photometric measurements confirm the rotation period of the asteroid to be 4.126 +/- 0.179 hours, consistent with the previously published value of 4.112 +/- 0.001 hours. By combining our visible spectroscopic measurements (0.45 - 0.93 microns) with archival MITHNEOS near infrared spectra (0.78 - 2.49 microns), we classify the asteroid as an Xn-type in the Bus-DeMeo taxonomy. The combined spectrum shows two weak absorption bands: Band I at 0.926 +/- 0.003 microns and Band II at 2.07 +/- 0.02 microns with band depths of 4.5 +/- 0.15% and 4.0 +/- 0.21%, respectively. The band area ratio is 1.13 +/- 0.05. These spectral band parameters plot at the tip of the S(IV) region of the Gaffey S-asteroid subtypes plot suggesting an affinity to ordinary chondrite meteorites. We calculated the chemistry of the olivine and pyroxene using the Band I center to be 20.1 +/- 2.3 mol% fayalite and 18.2 +/- 1.5 mol% ferrosilite, consistent with H chondrites. Principal component analysis of 1998 OR2's combined visible-NIR spectrum fall on the C/X-complex side of the alpha-line, near the end of the shock darkening trend, consistent with its weak absorption bands (band depth < 5%). We use an aerial mixing model with lab measurements of the shock darkened H5 chondrite, Chergach, to constrain the amount of shock darkened material on the asteroid's surface at ~63% dark lithology and ~37% light lithology.
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