Magazine article Science News

Sunstruck: Solar Hurricanes Rip Comet's Tail

Magazine article Science News

Sunstruck: Solar Hurricanes Rip Comet's Tail

Article excerpt

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.

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.

The cutting of 2P/Encke's tail was observed by one of a pair of spacecraft, called STEREO, that study the sun (SN: 3/3/07, p. 133). The images provide new insight into the magnetic interplay between comets and solar explosions, says Angelos Vourlidas of the Naval Research Laboratory in Washington, D.C. He and his colleagues describe the event in the Oct. 10 Astrophysical Journal Letters.

An amateur astronomer first discovered the cometary rip in a movie of STEREO images routinely posted online. He alerted Vourlidas and his colleagues that on April 20, the tail had been crunched, then severed. "Everyone was speechless, recalls Vourlidas.


In replaying the movie, the team saw that a coronal mass ejection (CME)--a magnetized cloud of charged particles thrown out from the sun's outer atmosphere--had swept past 2P/Encke just as the comet lost its ion tail. …

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