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Ceres' shape is controlled mainly by gravity and spin, with only a 3% departure from hydrostatic equilibrium. Its best-fit shape is a triaxial ellipsoid with dimensions a = 483.1 km, b = 481.0, km and c = 445.9 km, with c being the north-south axis and a and b the semimajor and semiminor equatorial axes.
The largest of these may have a hydrostatic-equilibrium shape, but most are irregular. Most of the trans-Neptunian objects (TNOs) listed with a radius smaller than 200 km have " assumed sizes based on a generic albedo of 0.09" since they are too far away to directly measure their sizes with existing instruments.
Ceres (minor-planet designation: 1 Ceres) is a dwarf planet in the middle main asteroid belt between the orbits of Mars and Jupiter. It was the first known asteroid , discovered on 1 January 1801 by Giuseppe Piazzi at Palermo Astronomical Observatory in Sicily , and announced as a new planet .
For planet Earth, which can be approximated as an oblate spheroid with radii 6 378.1 km and 6 356.8 km, the mean radius is = (( ) ) / = .The equatorial and polar radii of a planet are often denoted and , respectively.
Ceres is saturated with impact craters.Many have a central pit or bright spot. In the first batch of 17 names approved by the IAU, craters north of 20° north latitude had names beginning with A–G (with Asari being the furthest north), those between 20° north and south latitude beginning with H–R, and those further south beginning with S–Z (with Zadeni being the furthest south).
Only one of them – Pluto – has been observed in enough detail to verify that its current shape fits what would be expected from hydrostatic equilibrium. [53] Ceres is close to equilibrium, but some gravitational anomalies remain unexplained. [54] Eris is generally assumed to be a dwarf planet because it is more massive than Pluto.
Size comparison between the Moon, Neptune's moon Triton, Pluto, several large TNOs, and the dwarf planet Ceres. Their respective shapes are not represented. Characteristically, big (bright) objects are typically on inclined orbits, whereas the invariable plane regroups mostly small and dim objects. [21] It is difficult to estimate the diameter ...
The number of dwarf planets in the Solar System is unknown. Estimates have run as high as 200 in the Kuiper belt [1] and over 10,000 in the region beyond. [2] However, consideration of the surprisingly low densities of many large trans-Neptunian objects, as well as spectroscopic analysis of their surfaces, suggests that the number of dwarf planets may be much lower, perhaps only nine among ...