![]() A comet's ion tail always points away from the sun, whether the body is traveling toward or away from the sun along the comet's elliptical orbit. The interaction between comets' tails and the solar wind has been studied for decades. In 1996, Ulysses passed through the tail of comet Hyakutake and measurements indicated its tail didn't slow the solar wind at all. It will be a serious challenge for us theoreticians and computer modelers to figure out the physics." "Way past the orbit of Mars, the solar wind felt the disturbance of this little comet. "This was very surprising to me," Combi said. The solar wind would usually be about 435 miles per second at that distance from the sun, but inside the comet's ion tail, it was less than 249 miles per second. SWICS also found that even at 160 million miles from the comet's nucleus, the tail had slowed the solar wind to half its normal speed. ![]() The comet served as a source of electrons, said Michael Combi, a U-M space science professor who is an author of the paper. ![]() This suggests that the solar wind ions, originally missing most of their electrons, picked up some of their missing electrons when they passed through McNaught's atmosphere. Not only did SWICS detect unexpected ions in the comet tail, it found that the tail had a major impact on the surrounding solar wind.įor the first time at a comet, researchers detected O 3+ oxygen ions (atoms of oxygen with a positive charge because they have five electrons instead of eight). The solar wind consists of high-speed streams of plasma that emanate from the sun's outer atmosphere. ![]() Gloeckler is the principal investigator on the Solar Wind Ion Composition Spectrometer (SWICS) aboard Ulysses, which measured the composition and speed of the comet tail and solar wind. Instrument readings showed there was "complex chemistry" at play, said U-M space science professor George Gloeckler, second author of a paper on the findings published Oct. In February, it flew through McNaught's ion tail 160 million miles from the comet's core. The NASA/European Space Agency spacecraft is on a mission to study the sun's polar regions, and it carries an instrument run by U-M professors. So a chance encounter between spacecraft Ulysses and Comet McNaught's ion tail has scientists in the University of Michigan's College of Engineering marveling at a stroke of luck and some surprising data. ![]()
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