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This is a partial list of Solar System objects by size, arranged in descending order of mean volumetric radius, and subdivided into several size classes. These lists can also be sorted according to an object's mass and, for the largest objects, volume, density and surface gravity, insofar as these values are available. This list contains the Sun, the planets, dwarf planets, many of the larger small Solar System bodies (which includes the asteroids), all named natural satellites, and a number of smaller objects of historical or scientific interest, such as comets and near-Earth objects. The ordering may be different depending on whether one chooses radius or mass, because some objects are denser than others. For instance, Uranus is larger than Neptune but less massive, and although Ganymede and Titan are larger than Mercury, they have less than half Mercury's mass. This means some objects in the lower tables, despite their smaller radii, may be more massive than objects in the upper tables because they have a higher density. Many trans-Neptunian objects (TNOs) have been discovered, and their approximate locations in this list are shown, even though there can be a large uncertainty in their measurement. Solar System objects more massive than 1021 kilograms (one yottagram ()) are known or expected to be approximately spherical. Astronomical bodies relax into rounded shapes (ellipsoids), achieving hydrostatic equilibrium, when the gravity of their mass is sufficient to overcome the structural strength of their material. Objects made of ice become round more easily than those made of rock, and many icy objects are spheroidal at far lower sizes. The cutoff boundary for roundness is somewhere between 100 km and 200 km in radius. The larger objects in the mass range between 1018 kg to 1021 kg (1 to 1000 zettagrams ()), such as Tethys, Ceres, and Mimas, have relaxed to an oblate-spheroid equilibrium due to their gravity, whereas the less massive rubble piles (e.g. Amalthea and Janus) are roughly rounded, but not spherical, dubbed "irregular". Spheroidal bodies typically have some polar flattening due to the centrifugal force from their rotation, and can sometimes even have quite different equatorial diameters (scalene ellipsoids such as ). Unlike bodies such as Haumea, the irregular bodies deviate significantly from the shape of an ellipsoid. There can be difficulty in figuring out the diameter (within a factor of about 2) for typical objects beyond Saturn. (See 2060 Chiron as an example.) For TNOs there is some confidence in the diameters, but for non-binary TNOs there is no real confidence in the masses/densities. Many TNOs are often just assumed to have Pluto's density of 2.0 g/cm3, but it is just as likely that they have a comet-like density of only 0.5 g/cm3. For example, if a TNO is poorly assumed to have a mass of 3.59 kg based on a radius of 350 km with a density of 2 g/cm3 and is later discovered to only have a radius of 175 km with a density of 1 g/cm3, the mass estimate would be only 2.24 kg. The sizes and masses of many of the moons of Jupiter and Saturn are fairly well known due to numerous observations and interactions of the ''Galileo'' and ''Cassini'' orbiters. But many of the moons with a radius less than ~100 km, such as Jupiter's Himalia, still have unknown masses. Again, as we get further from the Sun than Saturn, things get less clear. There has not yet been an orbiter around Uranus or Neptune for long-term study of their moons. For the small outer irregular moons of Uranus, such as Sycorax, which were not discovered by the ''Voyager 2'' flyby, even different NASA web pages, such as the National Space Science Data Center and JPL Solar System Dynamics,〔 have somewhat contradictory size and albedo estimates depending on which research paper is being cited. Data for objects has varying reliability including uncertainties in the figures for mass and radius, and irregularities in the shape and density, with accuracy often depending on how close it is to Earth or if it has been visited by a probe. == Graphical overview == File:Sun vs planets en.svg|Relative masses of the bodies of the Solar System. Objects smaller than Saturn are not visible at this scale. File:Masses of the planets en.svg|Relative masses of the Solar planets. Jupiter at 71% of the total and Saturn at 21% dominate the system. Mercury is not visible at this scale. File:Masses of Solid Solar System bodies en.svg|Relative masses of the solid bodies of the Solar System. Earth at 48% and Venus at 39% dominate. Bodies less massive than Pluto are not visible at this scale. File:Masses of all moons.png|Relative masses of the rounded moons of the Solar System. Mimas, Enceladus, and Miranda are too small to be visible at this scale. Here, the Moon is labeled "Luna". 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「List of Solar System objects by size」の詳細全文を読む スポンサード リンク
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