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arXiv 1503.03885astro-ph.EP
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火星撞击流及其季节变化

The current impact flux on Mars and its seasonal variation

Youngmin JeongAhn, Renu Malhotra

摘要:

我们计算了现今火星上的撞击通量及其在火星年的变化,使用目前已知的火星穿越小行星的轨道分布数据。我们适应的Pik-Wetherill公式计算碰撞概率,注意到近日点经度的非均匀分布和长期行星摄动的近日点的参数。我们发现,这些以前被忽视的非均匀性有显着的影响,以及其季节变化的平均年影响通量。当火星在远日点时,撞击通量达到峰值,但火星的偏心率矢量与火星穿越者的偏心率矢量的平均方向接近一致,导致平均年撞击通量以及季节变化的幅度显着低于基于火星穿越者近日点距离均匀随机分布的估计。我们估计,在火星远日点$\pm30^\circ$内的大型撞击物(绝对星等为$H<16$)的通量大约是火星在近日点附近时的四倍。我们的结果外推到一个模型人口米大小的火星交叉表明,如果这些小的撞击有一个均匀分布的角度元素,那么他们的远日点到近日点的影响流量比将高达25。这些理论预测可以用目前在火星轨道上的航天器提供的当代撞击的观测数据来检验。

英文摘要:

We calculate the present-day impact flux on Mars and its variation over the Martian year, using the current data on the orbital distribution of known Mars-crossing minor planets. We adapt the {Ö}pik-Wetherill formulation for calculating collision probabilities, paying careful attention to the non-uniform distribution of the perihelion longitude and the argument of perihelion owed to secular planetary perturbations. We find that these previously neglected non-uniformities have a significant effect on the mean annual impact flux as well as its seasonal variation. The impact flux peaks when Mars is at aphelion, but the near-alignment of Mars' eccentricity vector with the mean direction of the eccentricity vectors of Mars-crossers causes the mean annual impact flux as well as the amplitude of the seasonal variation to be significantly lower than the estimate based on a uniform random distribution of perihelion longitudes of Mars-crossers. We estimate that the flux of large impactors (of absolute magnitude $H<16$) within $\pm30^\circ$ of Mars' aphelion is about four times larger than when the planet is near perihelion. Extrapolation of our results to a model population of meter-size Mars-crossers shows that if these small impactors have a uniform distribution of their angular elements, then their aphelion-to-perihelion impact flux ratio would be as large as 25. These theoretical predictions can be tested with observational data of contemporary impacts that is becoming available from spacecraft currently in orbit about Mars.

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