[论文解读] On the V-type asteroids outside the Vesta family. I. Interplay of nonlinear secular resonances and the Yarkovsky effect: the cases of 956 Elisa and 809 Lundia

V. Carruba, T. A. Michtchenko+3 more|ArXiv.org|Jun 27, 2005

Astro and Planetary Science参考文献 28被引用 70

一句话总结

本文提出，V型小行星956 Elisa和809 Lundia起源于灶神星族，但通过两步动力学机制向外迁移：首先通过三体共振和弱长期共振（受Yarkovsky效应驱动），随后被捕获进入强非线性长期共振$z_2$（$2(g-g_6)+s-s_6$）。模拟结果表明，只有直径大于约8公里的小行星才能在这些共振中存活足够长时间以抵达$z_2$共振，从而解释其大尺寸和共振轨道，并为灶神星族设定12亿年以上的年龄下限。

ABSTRACT

Among the largest objects in the main belt, asteroid 4 Vesta is unique in showing a basaltic crust. It is also the biggest member of the Vesta family, which is supposed to originate from a large cratering event about 1 Gyr ago (Marzari et al. 1996). Most of the members of the Vesta family for which a spectral classification is available show a V-type spectra. Before the discovery of 1459 Magnya (Lazzaro et al. 2000) and of several V-type NEA (Xu 1995), all the known V-type asteroids were members of the Vesta family. Recently two V-type asteroids, 809 Lundia and 956 Elisa, (Florczak et al. 2002) have been discovered well outside the limits of the family, near the Flora family. We currently know 22 V-type asteroids outside the family, in the inner asteroid belt. In this work we investigate the possibility that these objects are former family members that migrated to their current positions via the interplay of Yarkovsky effect and nonlinear secular resonances. The main dynamical feature of 956 Elisa and 809 Lundia is that they are currently inside the 2(g-g6)+s-s6 (z2 by Milani and Knezevic, 1993) secular resonance. Our investigations show that members of the Vesta dynamical family may drift in three-body and weak secular resonances until they are captured in the strong z2 secular resonance. Only asteroids with diameters larger than 16 km can remain in one of the three-body or secular resonances long enough to reach the region of the z2 resonance. This two-step mechanism of capture into the z2 resonance could explain: i) the current resonant orbits of 956 Elisa and 809 Lundia, ii) why their size is significantly larger than that of the typical member of the Vesta family, and iii) provide a lower limit on the Vesta family age.

研究动机与目标

• 研究位于灶神星族之外但具有辉石光谱的V型小行星956 Elisa和809 Lundia的动力学起源。
• 确定这些小行星是否可通过长期共振和非引力力从灶神星族迁移而来。
• 评估Yarkovsky效应和非线性长期共振在塑造外侧V型小行星当前轨道分布中的作用。
• 基于迁移 timescale 确定灶神星族的年龄下限。
• 识别目前可能被捕获在$z_2$长期共振中的其他V型小行星。

提出的方法

• 进行了数值N体模拟，以追踪从灶神星族中以与10亿年前撞击事件一致的初始速度弹射出的测试粒子的轨道演化。
• 将Yarkovsky效应建模为一种长期的非引力力，导致半长轴发生缓慢累积变化，通过改变热参数和粒子尺寸（10–8000米）来评估尺寸依赖性。
• 使用本征元素空间识别动力学家族和共振结构，明确追踪$z_2$长期共振（$2(g-g_6)+s-s_6$）。
• 应用层次聚类方法，在本征元素空间中识别956 Elisa和809 Lundia的潜在动力学邻近天体，使用130 m/s的速度截止值和绝对星等≤14.5。
• 通过将粒子轨道积分长达600万年，分析共振捕获和驻留时间，重点关注进入和穿越$z_2$共振的过程。
• 利用光谱分类数据和轨道接近度，评估其他V型小行星当前被捕获在$z_2$共振中的可能性。

实验结果

研究问题

• RQ1 956 Elisa和809 Lundia的当前共振轨道能否通过从灶神星族的动力学迁移来解释？
• RQ2 Yarkovsky效应在实现长期漂移进入强长期共振中起到什么作用？
• RQ3 为何956 Elisa和809 Lundia比典型的灶神星族成员大得多？
• RQ4 从迁移时间尺度推断，灶神星族的年龄下限是多少？
• RQ5 是否存在其他目前被捕获在$z_2$长期共振中的V型小行星，可能遵循相同的迁移路径？

主要发现

• 只有直径大于约8公里的小行星才能在三体共振和弱长期共振中存活足够长时间，以抵达$z_2$共振，从而解释956 Elisa和809 Lundia的大尺寸。
• 从灶神星族迁移至956 Elisa当前位置的典型时间尺度至少为12亿年，为灶神星族的年龄设定了下限。
• 小行星在$z_2$长期共振中停留约10亿年，之后被弹射至更强的平均运动共振，如7:2共振。
• $z_2$长期共振起到捕获陷阱的作用，模拟显示粒子可通过Yarkovsky效应驱动的演化，从较弱共振中漂移并被捕获进入$z_2$共振。
• 在本征元素空间中，于809 Lundia和956 Elisa附近识别出若干V型小行星候选体，全部目前位于$z_2$共振内，表明它们可能遵循相同的迁移路径。
• 4278 Harvey（一个已确认的V型小行星）位于共振附近，支持了所用识别方法的有效性。