C17/P Holmes is now the largest object in the Solar system:
GIANT COMET: "Formerly, the sun was the largest object in the Solar System," says University of Hawaii astronomer David Jewett. "Now, Comet 17P/Holmes holds that distinction." On Nov. 9th, a team of Hawaii astronomers led by Rachel Stevenson measured the diameter of the comet's expanding debris cloud: 1.4 million kilometers, slightly larger than the sun itself.
This composite image prepared by Jewett shows a Nov. 9th photo of the comet beside the sun and Saturn for scale. To photograph the comet, Stevenson et al used the 3.6 meter Canada-France-Hawaii Telescope atop Mauna Kea, "one of the few professional instruments still capable of capturing the whole comet in one image," notes Jewett.
From
SpaceWeather.com