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Eris has been measured at 2,326 ± 12 kilometres (1,445 ± 7 mi) in diameter; [12] its mass is 0.28% that of the Earth and 27% greater than that of Pluto, [23] [24] although Pluto is slightly larger by volume. [25] Both Eris and Pluto have a surface area that is comparable to that of Russia or South America. Eris has one large known moon, Dysnomia.
Michael E. Brown, discoverer of the scattered object Eris, suggests that its paler colour could be because, at its current distance from the Sun, its atmosphere of methane is frozen over its entire surface, creating an inches-thick layer of bright white ice.
This list does not include small Solar System bodies, but it does include a sample of possible planetary-mass objects whose shapes have yet to be determined. The Sun's orbital characteristics are listed in relation to the Galactic Center , while all other objects are listed in order of their distance from the Sun.
Ceres displays such evidence of an active geology as salt deposits and cryovolcanos, while Pluto has water-ice mountains drifting in nitrogen-ice glaciers, as well as a significant atmosphere. Ceres evidently has brine percolating through its subsurface, while there is evidence that Pluto has an actual subsurface ocean.
In February 2016, Eris's distance from the Sun was 96.3 AU (14.41 billion km; 8.95 billion mi), more than three times that of Neptune or Pluto. With the exception of long-period comets , Eris and Dysnomia were the most distant known natural objects in the Solar System until the discovery of 2018 AG 37 and 2018 VG 18 in 2018.
Thus, the Sun occupies 0.00001% (1 part in 10 7) of the volume of a sphere with a radius the size of Earth's orbit, whereas Earth's volume is roughly 1 millionth (10 −6) that of the Sun. Jupiter, the largest planet, is 5.2 AU from the Sun and has a radius of 71,000 km (0.00047 AU; 44,000 mi), whereas the most distant planet, Neptune, is 30 AU ...
Triton is large enough to have achieved hydrostatic equilibrium, but, uniquely for a large moon, has a retrograde orbit, suggesting it was a dwarf planet that was captured. Neptune also has seven known inner regular satellites, and eight outer irregular satellites. Pluto, a dwarf planet, has five moons.
Consequently, the thin optical surface layer could be quite different from the regolith underneath, and not representative of the bulk composition of the body. Small TNOs are thought to be low-density mixtures of rock and ice with some organic ( carbon -containing) surface material such as tholins , detected in their spectra.