阿罗科斯的项链
Arrokoth's Necklace
摘要：
（486958）Arrokoth（Ultima Thule，2014 MU $_{69}$）的飞越图像显示颈部有一条相对明亮的“项链”，或其两个裂片之间的裂缝，与其通常较低的宽度形成对比。我们认为，项链可能是热控制的冰沉积的结果。项链是在其表面最（轨道平均）的阴影部分。它可能由干净的、高沸点的冰组成，这些冰是由其他地方肮脏的、低沸点的冰升华而成的;干净的冰聚集在最高温度最低的地方。氨和丙烷具有必需的中挥发蒸气压。原始太阳系周围的气体将促进分子的再沉积，这些分子被表面较温暖的部分升华到裂缝中，同时也使表面平滑，并通过流体动力学阻力解释了阿罗科斯缓慢的旋转（与其分裂速率相比）。或者，一层足够厚的白霜（$\gtrsim 0.1\,μ$）可能是最近形成的。
英文摘要：
Flyby images of (486958) Arrokoth (Ultima Thule, 2014 MU$_{69}$) show a comparatively bright "necklace" in the neck, or cleft between its two lobes, in contrast to its generally low albedo. We suggest that the necklace may be the result of thermally controlled ice deposition. The necklace is found in the most (orbitally averaged) shaded part of its surface. It may consist of clean, high albedo, ice condensed from vapor sublimed by dirty, low albedo, ice elsewhere; clean ice accumulates where the maximum temperatures are the lowest. Ammonia and propane have the necessary mesovolatile vapor pressure. Surrounding gas in the proto-Solar System would facilitate redeposition of molecules sublimed by warmer parts of the surface into the cleft, as well as smoothing the surface and explaining, by hydrodynamic drag, Arrokoth's slow (compared to its breakup rate) rotation. Alternatively, a layer of hoarfrost thick enough ($\gtrsim 0.1\,μ$) to have a high albedo could have formed more recently.
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