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These lists contain 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.
Three of the four inner planets (Venus, Earth, and Mars) have atmospheres substantial enough to generate weather; all have impact craters and tectonic surface features, such as rift valleys and volcanoes. [91] Mercury (0.31–0.59 AU from the Sun) [D 6] is the smallest planet in the Solar System.
Alan Stern calls these satellite planets, although the term major moon is more common. The smallest natural satellite that is gravitationally rounded is Saturn I Mimas (radius 198.2 ± 0.4 km). This is smaller than the largest natural satellite that is known not to be gravitationally rounded, Neptune VIII Proteus (radius 210 ± 7 km).
The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a young protostar orbited by a protoplanetary disk. There are eight planets within the Solar System; planets outside of the solar system are also known as exoplanets.
Earth has one Moon, the largest moon of any rocky planet in the Solar System and the largest body typically described as a moon that orbits anything in hydrostatic equilibrium in relation to the primary object by mass and diameter other than Charon and Pluto, the latter two being dwarf planets revolving around each other. Earth also has more ...
An extrasolar planet in an orbit close to its star (normally less than one astronomical unit away), with a mass similar to that of Uranus or Neptune. Inferior planets: Planets whose orbits lie within the orbit of Earth. [nb 1] Inner planet: A planet in the Solar System that have orbits smaller than the asteroid belt. [nb 2] Outer planet
On the basis of that data, scientists have a first-order understanding of the geology and history of the planet. [4] [5] Mercury's surface shows intercrater plains, basins, smooth plains, craters, and tectonic features. Mercury's oldest surface is its intercrater plains, [4] [6] which are present (but much less extensive) on the Moon.
Approximate sizes of the planets relative to each other. Outward from the Sun, the planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Jupiter's diameter is about 11 times that of the Earth's and the Sun's diameter is about 10 times Jupiter's. The planets are not shown at the appropriate distance from the Sun.