NASA's Cassini spacecraft detected a record-breaking comet 18 years ago. The comet's tail was so long that it stretched for more than seven times the distance between Earth and the sun. Geraint Jones at University College London and his colleagues looked through data from the mission collected in 2002, when Cassini was on its way from Jupiter to Saturn. The spacecraft used its plasma instrument from 2001 to 2003 to study charged particles from the sun called the solar wind. Jones and his team found a notable increase in protons detected by the spacecraft in March 2002. The culprit appears to have been hydrogen ions pushed off a comet called 153P/lkeya-Zhang by the solar wind. "It matches up really well," says Jones.
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