page_title: Scattered disc
section_title: Comets
hierarchical_section_title: Scattered disc / Comets
caption_attribution_description: This image shows comet Tempel 1 approximately 5 minutes before Deep Impact's probe smashed into its surface. It was taken by the probe's impactor targeting sensor. The Sun is to the right of the image and reveals terrain varying in brightness by a factor of two. Shadows and bright areas indicate surface topography. Smooth regions with no features (lower left and upper right) are probably younger than rougher areas with circular features, which are probably impact craters. The probe crashed between the two dark-rimmed craters near the center and bottom of the comet. The nucleus is estimated to be about 5 kilometers (3.1 miles) across and 7 (4.3 miles) kilometers tall.
context_page_description: The scattered disc is a distant circumstellar disc in the Solar System that is sparsely populated by icy small solar system bodies, which are a subset of the broader family of trans-Neptunian objects. The scattered-disc objects have orbital eccentricities ranging as high as 0.8, inclinations as high as 40°, and perihelia greater than 30 astronomical units. These extreme orbits are thought to be the result of gravitational "scattering" by the gas giants, and the objects continue to be subject to perturbation by the planet Neptune.
  Although the closest scattered-disc objects approach the Sun at about 30–35 AU, their orbits can extend well beyond 100 AU. This makes scattered objects among the coldest and most distant objects in the Solar System. The innermost portion of the scattered disc overlaps with a torus-shaped region of orbiting objects traditionally called the Kuiper belt, but its outer limits reach much farther away from the Sun and farther above and below the ecliptic than the Kuiper belt proper.
context_section_description: The Kuiper belt was initially thought to be the source of the Solar System's ecliptic comets. However, studies of the region since 1992 have shown that the orbits within the Kuiper belt are relatively stable, and that ecliptic comets originate from the scattered disc, where orbits are generally less stable.
  Comets can loosely be divided into two categories: short-period and long-period—the latter being thought to originate in the Oort cloud. The two major categories of short-period comets are Jupiter-family comets (JFCs) and Halley-type comets. Halley-type comets, which are named after their prototype, Halley's Comet, are thought to have originated in the Oort cloud but to have been drawn into the inner Solar System by the gravity of the giant planets, whereas the JFCs are thought to have originated in the scattered disc. The centaurs are thought to be a dynamically intermediate stage between the scattered disc and the Jupiter family.
  There are many differences between SDOs and JFCs, even though many of the Jupiter-family comets may have originated in the scattered disc. Although the centaurs share a reddish or neutral coloration with many SDOs, their nuclei are bluer, indicating a fundamental chemical or physical difference. One hypothesis is that comet nuclei are resurfaced as they approach the Sun by subsurface materials which subsequently bury the older material.
caption: Tempel 1, a Jupiter-family comet
exif: {"Image ImageWidth": "500", "Image ImageLength": "500", "Image BitsPerSample": "8", "Image Compression": "Uncompressed", "Image PhotometricInterpretation": "1", "Image FillOrder": "1", "Image DocumentName": "Standard Input", "Image ImageDescription": "converted PNM file", "Image StripOffsets": "[8, 8008, 16008, 24008, 32008, 40008, 48008, 56008, 64008, 72008, 80008, 88008, 96008, 104008, 112008, 120008, 128008, 136008, 144008, 152008, 160008, 168008, 176008, 184008, 192008, 200008, 208008, 216008, 224008, 232008, 240008, 248008]", "Image Orientation": "Horizontal (normal)", "Image SamplesPerPixel": "1", "Image RowsPerStrip": "16", "Image StripByteCounts": "[8000, 8000, 8000, 8000, 8000, 8000, 8000, 8000, 8000, 8000, 8000, 8000, 8000, 8000, 8000, 8000, 8000, 8000, 8000, 8000, 8000, 8000, 8000, 8000, 8000, 8000, 8000, 8000, 8000, 8000, 8000, 2000]", "Image PlanarConfiguration": "1", "Image ExifOffset": "2582", "Image XPTitle": "[99, 0, 111, 0, 110, 0, 118, 0, 101, 0, 114, 0, 116, 0, 101, 0, 100, 0, 32, 0, 80, 0, 78, 0, 77, 0, 32, 0, 102, 0, 105, 0, 108, 0, 101, 0, 0, 0]", "Image XPSubject": "[99, 0, 111, 0, 110, 0, 118, 0, 101, 0, 114, 0, 116, 0, 101, 0, 100, 0, 32, 0, 80, 0, 78, 0, 77, 0, 32, 0, 102, 0, 105, 0, 108, 0, 101, 0, 0, 0]", "Image Padding": "[]", "EXIF Padding": "[]"}