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The structure of rocky planets is constrained by the average density of a planet and its moment of inertia. [15] The moment of inertia for a differentiated planet is less than 0.4, because the density of the planet is concentrated in the center. [16] Mercury has a moment of inertia of 0.346, which is evidence for a core. [17]
In the warmer inner Solar System, planetesimals formed from rocks and metals cooked billions of years ago in the cores of massive stars. These elements constituted only 0.6% of the material in the solar nebula. That is why the terrestrial planets could not grow very large and could not exert a strong pull on hydrogen and helium gas. [3]
Many TNOs are often just assumed to have Pluto's density of 2.0 g/cm 3, but it is just as likely that they have a comet-like density of only 0.5 g/cm 3. [ 4 ] For example, if a TNO is incorrectly assumed to have a mass of 3.59 × 10 20 kg based on a radius of 350 km with a density of 2 g/cm 3 but is later discovered to have a radius of only 175 ...
Within the Solar System, the terrestrial planets accepted by the IAU are the inner planets closest to the Sun: Mercury, Venus, Earth and Mars. Among astronomers who use the geophysical definition of a planet, two or three planetary-mass satellites – Earth's Moon, Io, and sometimes Europa – may also be considered terrestrial planets.
The outer planets Jupiter, Saturn, Uranus and Neptune, compared to the inner planets Earth, Venus, Mars, and Mercury at the bottom right The four outer planets, called giant planets or Jovian planets, collectively make up 99% of the mass orbiting the Sun. [ h ] All four giant planets have multiple moons and a ring system, although only Saturn's ...
Eventually, the Sun will likely expand sufficiently to overwhelm the inner planets (Mercury, Venus, and possibly Earth) but not the outer planets, including Jupiter and Saturn. Afterward, the Sun would be reduced to the size of a white dwarf , and the outer planets and their moons would continue orbiting this diminutive solar remnant.
Giant planets can significantly influence terrestrial planet formation. The presence of giants tends to increase eccentricities and inclinations (see Kozai mechanism) of planetesimals and embryos in the terrestrial planet region (inside 4 AU in the Solar System). [62] [66] If giant planets form too early, they can slow or prevent inner planet ...
The layers of the Earth, a differentiated planetary body. In planetary science, planetary differentiation is the process by which the chemical elements of a planetary body accumulate in different areas of that body, due to their physical or chemical behavior (e.g. density and chemical affinities).