spacetoday.net: Scientists see comets, sun interact

Posted: Tue, Oct 2, 2007, 8:03 AM ET (1203 GMT)
Comet tail detachment illustration (NASA)

A solar storm ripped away one comet's tail while another comet slowed down the solar wind far from the Sun, astronomers said on Monday. In one paper to be published this month in the Astrophysical Journal, NASA researchers reported how a coronal mass ejection collided with the comet Encke when the comet was about as far from the Sun as the planet Mercury. The collision, witnessed by the STEREO-A spacecraft in April 2007, ripped away the comet's tail. Researchers suspect that a process known as magnetic reconnection may have released enough energy to strip away the tail. Separately, University of Michigan scientists, in a paper in the same journal, reported on the interaction of the solar wind with the comet McNaught, as witnessed by instruments on the Ulysses spacecraft. Researchers found that the solar wind's velocity slowed by half after passing through the comet's ion tail, more than 250 million kilometers from the Sun. The physics of the interaction between the solar wind and comet tail remain unclear.