COLLISIONS BETWEEN GRAVITY-DOMINATED BODIES. I. OUTCOME REGIMES AND SCALING LAWS
COLLISIONS BETWEEN GRAVITY-DOMINATED BODIES. I. OUTCOME REGIMES AND SCALING LAWS
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DOI：
10.1088/0004-637x/745/1/79
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发表时间：
2012-01-20
影响因子：
4.9
通讯作者：
Stewart, Sarah T.
中科院分区：
文献类型：
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作者：
Leinhardt, Zoe M.;Stewart, Sarah T.
碰撞是行星形成的核心因素。在这项工作中，我们对受重力主导的天体之间的任何碰撞的动力学结果进行了分析描述。我们对小行星体之间的碰撞进行了高分辨率模拟；这些结果被用于分离不同撞击参数对碰撞结果的影响。在从小行星体到行星的成长过程中，碰撞结果涵盖多种情况：成坑、合并、瓦解、超灾难性瓦解以及撞击逃逸事件。我们推导出方程（标度律）来划分碰撞情况之间的转变，并描述碰撞后天体的大小和速度分布。这些标度律被用于计算作为质量比、撞击角度和撞击速度函数的碰撞结果图，我们还讨论了行星形成过程中每种碰撞情况的概率所产生的影响。碰撞结果是根据撞击条件和灾难性瓦解标准Q*(RD)——分散总碰撞质量一半所需的比能来描述的。所有行星形成和碰撞演化研究都假定灾难性瓦解遵循纯能量标度；然而，我们发现灾难性瓦解几乎遵循纯动量标度。因此，Q*(RD)除了与总质量和撞击角度有关外，还强烈依赖于撞击速度以及抛射体与目标的质量比。为了考虑撞击角度，我们推导出抛射体的相互作用质量分数；碰撞的结果取决于相互作用质量的动能，而非总质量的动能。我们还引入了一个新的物质参数c*，它以比引力结合能为单位定义了等质量天体之间的灾难性瓦解标准。对于各种各样的小行星体成分和内部结构，c*的值为5±2；而对于无强度的行星，我们发现c* = 1.9±0.3。我们将等质量天体的灾难性瓦解标准称为主瓦解曲线，它在任何碰撞情形下计算Q*(RD)时都被用作参考值。这项工作中提出的分析碰撞模型将显著改进行星形成和碰撞演化数值模拟中的碰撞物理过程。
Collisions are the core agent of planet formation. In this work, we derive an analytic description of the dynamical outcome for any collision between gravity-dominated bodies. We conduct high-resolution simulations of collisions between planetesimals; the results are used to isolate the effects of different impact parameters on collision outcome. During growth from planetesimals to planets, collision outcomes span multiple regimes: cratering, merging, disruption, super-catastrophic disruption, and hit-and-run events. We derive equations (scaling laws) to demarcate the transition between collision regimes and to describe the size and velocity distributions of the post-collision bodies. The scaling laws are used to calculate maps of collision outcomes as a function of mass ratio, impact angle, and impact velocity, and we discuss the implications of the probability of each collision regime during planet formation. Collision outcomes are described in terms of the impact conditions and the catastrophic disruption criteria, Q*(RD)-the specific energy required to disperse half the total colliding mass. All planet formation and collisional evolution studies have assumed that catastrophic disruption follows pure energy scaling; however, we find that catastrophic disruption follows nearly pure momentum scaling. As a result, Q*(RD) is strongly dependent on the impact velocity and projectile-to-target mass ratio in addition to the total mass and impact angle. To account for the impact angle, we derive the interacting mass fraction of the projectile; the outcome of a collision is dependent on the kinetic energy of the interacting mass rather than the kinetic energy of the total mass. We also introduce a new material parameter, c*, that defines the catastrophic disruption criteria between equal-mass bodies in units of the specific gravitational binding energy. For a diverse range of planetesimal compositions and internal structures, c* has a value of 5 +/- 2; whereas for strengthless planets, we find c* = 1.9 +/- 0.3. We refer to the catastrophic disruption criteria for equal-mass bodies as the principal disruption curve, which is used as the reference value in the calculation of Q*(RD) for any collision scenario. The analytic collision model presented in this work will significantly improve the physics of collisions in numerical simulations of planet formation and collisional evolution.