Ceres

There is a dwarf planet between Mars and Jupiter called Ceres

There is a mysterious dwarf planet between Mars and Jupiter called ‘Ceres’ which has never been visited by spacecraft or photographed in detail, however, Earth-bound telescopes reveal a large bright shining spot on the surface of this planet, the origin and nature of which are unknown.

Ceres is the largest object in the asteroid belt. The mass of Ceres has been determined by analysis of the influence it exerts on smaller asteroids. Results differ slightly between researchers. The average of the three most precise values as of 2008 is 9.4×1020 kg. With this mass Ceres comprises about a third of the estimated total 3.0 ± 0.2×1021 kg mass of the asteroid belt, which is in turn about 4% of the mass of the Moon. The surface area is approximately equal to the land area of India or Argentina. The mass of Ceres is sufficient to give it a nearly spherical shape in hydrostatic equilibrium. In contrast, other large asteroids such as 2 Pallas, 3 Juno, and in particular 10 Hygiea are known to be somewhat irregular in shape.

Ceres

Internal structure

Ceres’s oblateness is inconsistent with an undifferentiated body, which indicates that it consists of a rocky core overlain with an icy mantle. This 100-km-thick mantle (23%–28% of Ceres by mass; 50% by volume) contains 200 million cubic kilometers of water, which is more than the amount of fresh water on the Earth. This result is supported by the observations made by the Keck telescope in 2002 and by evolutionary modeling. Also, some characteristics of its surface and history (such as its distance from the Sun, which weakened solar radiation enough to allow some fairly low-freezing-point components to be incorporated during its formation), point to the presence of volatile materials in the interior of Ceres.

Alternatively, the shape and dimensions of Ceres may be explained by an interior that is porous and either partially differentiated or completely undifferentiated. The presence of a layer of rock on top of ice would be gravitationally unstable. If any of the rock deposits sank into a layer of differentiated ice, salt deposits would be formed. Such deposits have not been detected. Thus it is possible that Ceres does not contain a large ice shell, but was instead formed from low-density asteroids with an aqueous component. The decay of radioactive isotopes may not have been sufficient to cause differentiation.

Source