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Meteorites

The long trip to Earth

Nature volume 407, pages 573–575 (2000)Cite this article

In the 1790s, European scientists accepted the once preposterous notion that meteorites — rocks that fall from the skies — were of cosmic origin and not lightning bolts, volcanic ejecta, or the eighteenth- century equivalents of ghosts or UFOs. By coincidence, the first asteroid was discovered in space in 1801. As more asteroids were found, the idea naturally developed that meteorites were fragments of asteroids. Early theories that a planet had exploded to create the asteroid belt between Mars and Jupiter gave way to the modern understanding that asteroids are the left-over building blocks of a planet that never formed. Although meteoriticists continued to assume that these exotic rocks were asteroidal, physicists increasingly doubted that rocks could be moved intact from the asteroid belt to Earth. After 200 years of disparate astronomical observations of asteroids and laboratory studies of meteorites, a quantitative model, reported by David Vokrouhlický and Paolo Farinella on page 606 of this issue1, now shows how a suite of processes bring small asteroid fragments to Earth.

From a physics perspective, the simple billiard-ball analogy of collisions between rocks knocking each other around the inner Solar System does not stand up to elementary scrutiny. It is no easier to 'bump' icy, rocky or even metallic objects, with finite material strengths, from the asteroid belt into Earth-crossing orbits than it is to hit eggs around the fairways with a golf club. Much gentler accelerations are required, such as those exerted on comets at the edge of the Solar System by the gravity of passing stars and giant molecular clouds.

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  1. Southwest Research Institute , Suite 426, 1050 Walnut Street, Boulder, 80302, Colorado, USA

    Clark R. Chapman

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  1. Clark R. Chapman
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Correspondence to Clark R. Chapman.

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Chapman, C. The long trip to Earth. Nature 407, 573–575 (2000). https://doi.org/10.1038/35036666

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