By Ron Cowen
Comet 2P/Encke has been looping around the sun for thousands of years. But last April, just after the comet slipped inside Mercury’s orbit, magnetic hurricanes belching from the sun chopped off its ion tail. Spacecraft images of the event provide the first clear evidence of such a curtailment.
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As a comet nears the sun, it typically sports two tails—a brilliant dust tail and a fainter ion tail. The latter comes about as the solar wind, a breeze of charged particles blowing from the sun, sweeps ionized gas molecules from the comet’s nucleus into a tail that stretches for millions of kilometers into space. The wind also carries along a magnetic field that it drapes over the comet.