1 August 2002

Planetary science: Impact factor

Meteoritic craters on Earth are poor specimens, compared with those
elsewhere in the Solar System, having been eroded by wind, rain and geological activity. But a newly discovered impact structure has apparently been protected from the elements for some 65 million years. The 20-km diameter structure, found during prospecting for oil and gas beneath the North Sea, has been mapped by seismic imaging and may now be the best three-dimensionally imaged impact structure on Earth. It is 'multiringed', a feature not previously seen at such small scale on the terrestrial planets, and is comparable to the much larger Valhalla ring structure on the icy surface of Callisto.

A 20-km-diameter multi-ringed impact structure in the North Sea
SIMON A. STEWART AND PHILIP J. ALLEN
Nature 418, 520–523 (2002); doi:10.1038/nature00914
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Planetary science: Impacts in the round
JOHN G. SPRAY
A well-preserved crater has been identified deep beneath the bed of the North Sea. It may well have been produced by the impact of an extraterrestrial body some 60 million years ago.
Nature 418, 487–488 (2002); doi:10.1038/418487a
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