木星族彗星的升华力矩及其核上的物质坡移事件
The Sublimative Torques of Jupiter Family Comets and Mass Wasting Events on Their Nuclei
摘要：
彗星的升华释气产生的扭矩改变了其原子核的旋转状态。近年来，参数化升华力矩模型已被发展用于研究单个彗核和彗星群体的自转状态变化。然而，这些模型将逃逸气体和彗星表面之间的相互作用简化为几个参数，隐藏了这些复杂相互作用的细节。在这里，我们直接比较了X参数模型（Samarasinha & Mueller，2013）与SYORP模型（Steckloff & Jacobson，2016），以梳理出驱动升华扭矩的气体-表面相互作用的细节。我们发现，这两个模型，以准确地模拟升华扭矩，升华分子的数量，有助于净扭矩在很大程度上是独立的详细的形状和活动的核，而是主要取决于大小的核和有效的彗星的日心距离。我们认为，彗星的活动必须在很大程度上限制在陡峭的重力表面斜坡（以上的休止角），在那里的物质坡移可以通过脱落的地幔耐火材料和暴露新鲜的挥发物刷新活动。我们提出了一个新的分类方案，彗星的基础上，这种质量浪费过程的频率（相对于活动衰落的时间尺度）：准平衡，情节，准休眠和灭绝。
英文摘要：
Sublimative outgassing of comets produces torques that alter the rotation state of their nuclei. Recently, parameterized sublimative torque models have been developed to study rotation state changes of individual comet nuclei and populations of cometary bodies. However, these models simplify the interactions between the escaping gas and cometary surface into only a few parameters that hide the details of these complex interactions. Here we directly compare the X-parameter model (Samarasinha & Mueller, 2013) with the SYORP model (Steckloff & Jacobson, 2016) to tease out insights into the details of the gas-surface interactions driving sublimative torques. We find that, for both of these models to accurately model sublimative torques, the number of sublimating molecules that contribute to the net torque is largely independent of the detailed shape and activity of the nucleus, but rather depends primarily on the size of the nucleus and the effective heliocentric distance of the comet. We suggest that cometary activity must be largely restricted to regions of steep gravitational surface slopes (above the angle of repose), where mass wasting can refresh activity by shedding mantles of refractory materials and exposing fresh volatiles. We propose a new classification scheme for comets based on the frequency of this mass-wasting process (relative to the timescale of activity fading): quasi-equilibrium, episodic, quasi-dormant, and extinct.
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