433 Eros和1036 Ganymed表面存在OH或H2O的证据
Evidence for OH or H2O on the surface of 433 Eros and 1036 Ganymed
摘要：
水和羟基，曾经被认为只存在于形成于大约2.5-3天文单位之外的原始无空气天体中，最近在月球和灶神星上被发现，这两个天体的表面都由进化的非原始成分所主导。在这两种情况下，水/OH被认为是外生的，或者是通过彗星或水合小行星的撞击带来的，或者是通过太阳风与风化层中的硅酸盐相互作用产生的，或者两者兼而有之。这种外生过程也应该发生在其他无空气的物体表面。为了验证这一假设，我们使用美国宇航局红外望远镜设施（IRTF）测量了两颗大型近地小行星（NEAs）的反射光谱（2.0至4.1 μm），其组成通常被解释为无水：433 Eros和1036 Ganymed。OH在这两个物体上都以3 μm附近的吸收特征的形式被检测到。光谱包含一个较长波长的热发射成分，从中我们估计爱神星的热辐射为167+/- 98 J m-2s-1/2K-1（与以前的估计一致），Ganymed的热辐射为214+/- 80 J m-2s-1/2K-1，这是该天体首次报道的热惯性测量。这些观察结果表明，负责在大型无空气物体上产生水/OH的过程也作用于小得多的物体。
英文摘要：
Water and hydroxyl, once thought to be found only in the primitive airless bodies that formed beyond roughly 2.5-3 AU, have recently been detected on the Moon and Vesta, which both have surfaces dominated by evolved, non-primitive compositions. In both these cases, the water/OH is thought to be exogenic, either brought in via impacts with comets or hydrated asteroids or created via solar wind interactions with silicates in the regolith or both. Such exogenic processes should also be occurring on other airless body surfaces. To test this hypothesis, we used the NASA Infrared Telescope Facility (IRTF) to measure reflectance spectra (2.0 to 4.1 μm) of two large near-Earth asteroids (NEAs) with compositions generally interpreted as anhydrous: 433 Eros and 1036 Ganymed. OH is detected on both of these bodies in the form of absorption features near 3 μm. The spectra contain a component of thermal emission at longer wavelengths, from which we estimate thermal of 167+/- 98 J m-2s-1/2K-1 for Eros (consistent with previous estimates) and 214+/- 80 J m-2s-1/2K-1 for Ganymed, the first reported measurement of thermal inertia for this object. These observations demonstrate that processes responsible for water/OH creation on large airless bodies also act on much smaller bodies.
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