Why did Halley hiccup?

Abstract

Does anyone remember Halley's comet? It was in all the papers about five years ago, but since then not much has been heard about it. That is, not until the comet flared into brightness again in February of this year. The only problem was that the comet was over 14 astronomical units (14 AU, about 2,100 million km) from the Sun, between the orbits of Saturn and Uranus, a region of the Solar System so cold that it was believed that a comet nucleus would be totally inert there.

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