撞击坑和奥尔特云
Impact cratering and the Oort cloud
摘要：
我们计算预期的流量配置文件的彗星进入行星系统的奥尔特云所产生的银河系潮汐和遇到的分子云。我们发现，周期性和零星的轰击事件，振幅一个数量级以上的背景，发生在特征的时间尺度~25-35万年。在旋臂交叉期间优先发生的轰击事件可能是生命大规模灭绝的原因，也是活微生物从轰击地球转移到扰动星云的原因。在过去2.5亿年中，理论预期与大型、日期明确的陆地撞击坑的年龄分布之间存在良好的一致性。陨石坑记录中的弱周期性约为3600万年，这与太阳最近通过银道面相一致，并意味着中心面密度约为0.15 M_Sun pc^（-3）。这使得圆盘中几乎没有空间容纳重要的暗物质成分。
英文摘要：
We calculate the expected flux profile of comets into the planetary system from the Oort cloud arising from Galactic tides and encounters with molecular clouds. We find that both periodic and sporadic bombardment episodes, with amplitudes an order of magnitude above background, occur on characteristic timescales ~25-35 Myr. Bombardment episodes occurring preferentially during spiral arm crossings may be responsible both for mass extinctions of life and the transfer of viable microorganisms from the bombarded Earth into the disturbing nebulae. Good agreement is found between the theoretical expectations and the age distribution of large, well-dated terrestrial impact craters of the past 250 million years. A weak periodicity of ~36 Myr in the cratering record is consistent with the Sun's recent passage through the Galactic plane, and implies a central plane density ~0.15 M_Sun pc^(-3). This leaves little room for a significant dark matter component in the disc.
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