Heck Philipp R, Schmitz Birger, Baur Heinrich, Halliday Alex N, Wieler Rainer
ETH Zürich, Isotope Geology, NO C61, CH-8092 Zürich, Switzerland.
Nature. 2004 Jul 15;430(6997):323-5. doi: 10.1038/nature02736.
Very large collisions in the asteroid belt could lead temporarily to a substantial increase in the rate of impacts of meteorites on Earth. Orbital simulations predict that fragments from such events may arrive considerably faster than the typical transit times of meteorites falling today, because in some large impacts part of the debris is transferred directly into a resonant orbit with Jupiter. Such an efficient meteorite delivery track, however, has not been verified. Here we report high-sensitivity measurements of noble gases produced by cosmic rays in chromite grains from a unique suite of fossil meteorites preserved in approximately 480 million year old sediments. The transfer times deduced from the noble gases are as short as approximately 10(5) years, and they increase with stratigraphic height in agreement with the estimated duration of sedimentation. These data provide powerful evidence that this unusual meteorite occurrence was the result of a long-lasting rain of meteorites following the destruction of an asteroid, and show that at least one strong resonance in the main asteroid belt can deliver material into the inner Solar System within the short timescales suggested by dynamical models.
小行星带中发生的极大规模碰撞可能会暂时导致陨石撞击地球的速率大幅增加。轨道模拟预测，此类事件产生的碎片抵达地球的速度可能比如今坠落的陨石的典型渡越时间快得多，因为在一些大型撞击事件中，部分碎片会直接被转移到与木星的共振轨道上。然而，这种高效的陨石输送轨道尚未得到证实。在此，我们报告了对一组保存在约4.8亿年前沉积物中的独特化石陨石中铬铁矿颗粒内宇宙射线产生的惰性气体的高灵敏度测量结果。从惰性气体推断出的转移时间短至约10⁵年，并且它们随地层高度增加，这与估计的沉积持续时间一致。这些数据提供了有力证据，表明这种不寻常的陨石出现是小行星毁灭后长时间陨石雨的结果，并且表明主小行星带中至少有一个强共振能够在动力学模型所暗示的短时间尺度内将物质输送到内太阳系。
