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A Comet's Long Tail Tickles Ulysses

When a newly discovered comet named Hyakutake passed near Earth about 4 years ago, it made a major spectacle of itself. As well as flaunting two dust tails, it sported a ghostly bluish-white stream of charged particles, extending a third of the way across the sky (SN: 6/1/96, p. 346).

This ion tail, it now turns out, went on for an even longer stretch. A recent review of 1996 data from the Ulysses spacecraft reveals this tail as the longest ever recorded. Spanning at least 571 million kilometers—about 3.5 times the Earth-sun distance—the tail might have extended to the fringes of the solar system, researchers report in the April 6 Nature.

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