Libourel Guy, Nakamura Akiko M, Beck Pierre, Potin Sandra, Ganino Clément, Jacomet Suzanne, Ogawa Ryo, Hasegawa Sunao, Michel Patrick
Université Côte d'Azur, Observatoire de la Côte d'Azur, CNRS, Laboratoire Lagrange, Boulevard de l'Observatoire, CS 34229, 06304 Nice Cedex 4, France.
Hawai'i Institute of Geophysics and Planetology, School of Ocean, Earth Science and Technology, University of Hawai'i at Mānoa, Honolulu, HI 96821, USA.
Sci Adv. 2019 Aug 28;5(8):eaav3971. doi: 10.1126/sciadv.aav3971. eCollection 2019 Aug.
Several arguments point to a larger proportion of metal-rich asteroids than that derived from spectral observations, as remnants of collisional disruptions of differentiated bodies. We show experimentally that this apparent deficit may result from the coating of metallic surfaces by silicate melts produced during impacts of hydrated or dry projectiles at typical asteroid impact speeds. Spectral analysis of steel and iron meteorite targets after impact shows a profoundly modified optical signature. Furthermore, hydrated projectiles leave a 3-μm absorption hydration feature. This feature is thus consistent with a metallic surface and does not require an unusual low-speed impact. Unless systematizing radar measurements, ground-based spectral observations can be deceptive in identifying iron-rich bodies. The NASA Psyche mission rendezvous with Psyche will offer the unique opportunity both to measure the relative abundances of regolith and glassy coated surfaces and to substantially increase our understanding of impact processes and signatures on a metal-rich asteroid.
有几个论据表明，富金属小行星的比例比光谱观测得出的比例更大，它们是分异天体碰撞破裂的残余物。我们通过实验表明，这种明显的不足可能是由于水合或干燥抛射体以典型小行星撞击速度撞击时产生的硅酸盐熔体覆盖了金属表面所致。对撞击后的钢和铁陨石靶进行光谱分析，显示出光学特征发生了深刻变化。此外，水合抛射体会留下一个3微米吸收的水合特征。因此，这个特征与金属表面一致，并不需要异常的低速撞击。除非对雷达测量进行系统化，否则地面光谱观测在识别富铁天体时可能会产生误导。美国国家航空航天局（NASA）的“心灵号”任务与小行星“心灵号”交会，将提供独特的机会，既能测量风化层和玻璃涂层表面的相对丰度，又能大幅增进我们对富金属小行星撞击过程和特征的理解。
