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Thu Nov 8, 2018, 08:23 PM

Comet tails blowing in the solar wind

Date:
November 2, 2018
Source:
NASA/Goddard Space Flight Center



The Sun's magnetic field, which is embedded in the solar wind, permeates the entire solar system. The current sheet
-- where the magnetic field changes polarity --spirals out from near the solar equator like a wavy skirt around a ballet dancer's waist.
Credit: NASA's Goddard Space Flight Center

Engineers and scientists gathered around a screen in an operations room at the Naval Research Laboratory in Washington, D.C., eager to lay their eyes on the first data from NASA's STEREO spacecraft. It was January 2007, and the twin STEREO satellites -- short for Solar and Terrestrial Relations Observatory -- which had launched just months before, were opening their instruments' eyes for the first time. First up: STEREO-B. The screen blinked, but instead of the vast starfield they expected, a pearly white, feathery smear -- like an angel's wing -- filled the frame. For a few panicky minutes, NRL astrophysicist Karl Battams worried something was wrong with the telescope. Then, he realized this bright object wasn't a defect, but an apparition, and these were the first satellite images of Comet McNaught. Later that day, STEREO-A would return similar observations.

Comet C/2006 P1 -- also known as Comet McNaught, named for astronomer Robert McNaught, who discovered it in August 2006 -- was one of the brightest comets visible from Earth in the past 50 years. Throughout January 2007, the comet fanned across the Southern Hemisphere's sky, so bright it was visible to the naked eye even during the day. McNaught belongs to a rarefied group of comets, dubbed the Great Comets and known for their exceptional brightness. Setting McNaught apart further still from its peers, however, was its highly structured tail, composed of many distinct dust bands called striae, or striations, that stretched more than 100 million miles behind the comet, longer than the distance between Earth and the Sun. One month later, in February 2007, an ESA (European Space Agency) and NASA spacecraft called Ulysses would encounter the comet's long tail.

"McNaught was a huge deal when it came because it was so ridiculously bright and beautiful in the sky," Battams said. "It had these striae -- dusty fingers that extended across a huge expanse of the sky. Structurally, it's one of the most beautiful comets we've seen for decades."

How exactly the tail broke up in this manner, scientists didn't know. It called to mind reports of another storied comet from long ago: the Great Comet of 1744, which was said to have dramatically fanned out in six tails over the horizon, a phenomenon astronomers then couldn't explain. By untangling the mystery of McNaught's tail, scientists hoped to learn something new about the nature of comets -- and solve two cosmic mysteries in one.

More:
https://www.sciencedaily.com/releases/2018/11/181102131952.htm

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