A Gigantic Comet

Comet McNaught, the so-called Great Comet of 2007, has been identified as the biggest comet measured to date, according to scientists, whose calculations were based on the comet's overall influence in space.

Instead of using the length of the comet's tail to measure the scale of the comet, astronomers used data from the ESA/NASA Ulysses spacecraft to determine the size of the region of space disturbed by the comet's presence – a cosmic wake across the solar system.

Through analysis of magnetometer data, scientists found evidence of a decayed shockwave surrounding the comet, which was created when ionized gas emitted from the comet's nucleus joined the fast-flowing particles of the solar wind. That, in turn, caused the solar wind around the comet to abruptly slow down.…

See SPACE.com for links to further info.