Comet icon is included into Space Icons. You can view all icons here:[link]
Each artistic toolbar icon is available in sizes of 256x256, 48x48, 32x32, 24x24, 20x20, and 16x16 pixels. All images are supplied in ICO, PNG, GIF, and BMP formats. Your order will get you all icons in have 256 colors and True Color variants.
Download link: [link]