Major features of the Solar System (not to scale, from left to right): Pluto, Neptune, Uranus, Saturn, Jupiter, the asteroid belt, the Sun, Mercury, Venus, Earth & Moon, and Mars. A comet is also seen on the left. Solar System Portal
The Solar System or solar system[a] comprises the Sun and the retinue of celestial objects gravitationally bound to it: the eight planets, their 162 known moons,[1] three currently identified dwarf planets and their four known moons, and thousands of small bodies. This last category includes asteroids, meteoroids, comets, and interplanetary dust.
In broad terms, the charted regions of the Solar System consist of the Sun (astronomical symbol ), four rocky bodies close to it called the inner planets, an inner belt of rocky asteroids, four giant outer planets and a second belt of small icy bodies known as the Kuiper belt. In order of their distances from the Sun, the planets are Mercury (), Venus (), Earth (), Mars (), Jupiter (), Saturn (), Uranus (), and Neptune (). Six of the eight planets are in turn orbited by natural satellites (usually termed "moons" after Earth's Moon) and every planet past the asteroid belt is encircled by planetary rings of dust and other particles. All the planets, other than the Earth, are named after gods and goddesses from Greco-Roman mythology. The three dwarf planets are Pluto, (), the largest known Kuiper belt object, Ceres, (), the largest object in the asteroid belt, and Eris, which lies beyond the Kuiper belt in a region called the scattered disc.
Mercury
Mercury (0.4 AU) is the closest planet to the Sun and the smallest planet (0.055 Earth masses). Mercury has no natural satellites, and its only known geological features besides impact craters are "wrinkle ridges", probably produced by a period of contraction early in its history.[36] Mercury's almost negligible atmosphere consists of atoms blasted off its surface by the solar wind.[37] Its relatively large iron core and thin mantle have not yet been adequately explained. Hypotheses include that its outer layers were stripped off by a giant impact, and that it was prevented from fully accreting by the young Sun's energy.[38][39]
Venus
Venus (0.7 AU) is close in size to Earth (0.815 Earth masses), and, like Earth, has a thick silicate mantle around an iron core, a substantial atmosphere and evidence of internal geological activity. However, it is much drier than Earth and its atmosphere is ninety times as dense. Venus has no natural satellites. It is the hottest planet, with surface temperatures over 400 °C, most likely due to the amount of greenhouse gases in the atmosphere.[40] No definitive evidence of current geological activity has been detected on Venus, but it has no magnetic field that would prevent depletion of its substantial atmosphere, which suggests that its atmosphere is regularly replenished by volcanic eruptions.[41]
Earth
Earth (1 AU) is the largest and densest of the inner planets, and the only one known to have current geological activity. Earth is the only planet known to have life. Its liquid hydrosphere, unique among the terrestrial planets, is probably the reason Earth is also the only planet where plate tectonics has been observed, because water acts as a lubricant for subduction.[42] Earth's atmosphere is radically different from the other terrestrial planets, having been altered by the presence of life to contain 21 percent free oxygen.[43] Earth has one satellite, the Moon; the only large satellite of a terrestrial planet in the Solar System.
Mars
Mars (1.5 AU) is smaller than Earth and Venus (0.107 Earth masses). It possesses a tenuous atmosphere of carbon dioxide. Its surface, peppered with vast volcanoes such as Olympus Mons and rift valleys such as Valles Marineris, shows geological activity that may have persisted until very recently.[44] Mars has two tiny moons (Deimos and Phobos) thought to be captured asteroids.[45]
Jupiter
Jupiter (5.2 AU), at 318 Earth masses, masses 2.5 times all the other planets put together. It is composed largely of hydrogen and helium. Jupiter's strong internal heat creates a number of semi-permanent features in its atmosphere, such as cloud bands and the Great Red Spot. Jupiter has sixty-three satellites. The four largest, Ganymede, Callisto, Io, and Europa show similarities to the terrestrial planets, such as volcanism and internal heating.[52] Ganymede, the largest satellite in the Solar System, is larger than Mercury.
Saturn
Saturn (9.5 AU), famous for its extensive ring system, has similarities to Jupiter, such as its atmospheric composition. Saturn is far less massive, being only 95 Earth masses. Saturn has fifty-six moons; two, Titan and Enceladus, show signs of geological activity, though they are largely made of ice.[53] Titan is larger than Mercury and the only satellite in the solar system with a substantial atmosphere.
Uranus
Uranus (19.6 AU), at 14 Earth masses, is the lightest of the outer planets. Uniquely among the planets, it orbits the Sun on its side; its axial tilt is over ninety degrees to the ecliptic. It has a much colder core than the other gas giants, and radiates very little heat into space.[54] Uranus has twenty-seven satellites, the largest ones being Titania, Oberon, Umbriel, Ariel and Miranda.
Neptune
Neptune (30 AU), though slightly smaller than Uranus, is denser at 17 Earth masses. It radiates more internal heat, but not as much as Jupiter or Saturn.[55] Neptune has thirteen moons. The largest, Triton, is geologically active, with geysers of liquid nitrogen.[56] Triton is the only large satellite with a retrograde orbit. Neptune possesses a number of Trojan asteroids.
Pluto (39 AU average), a dwarf planet, is the largest known object in the Kuiper belt. When discovered in 1930 it was considered to be the ninth planet; this changed in 2006 with the adoption of a formal definition of planet. Pluto has a relatively eccentric orbit inclined 17 degrees to the ecliptic plane and ranging from 29.7 AU from the Sun at perihelion (within the orbit of Neptune) to 49.5 AU at aphelion.
It is unclear whether Charon, Pluto's largest moon, will continue to be classified as such or as a dwarf planet itself. Both Pluto and Charon orbit a barycenter of gravity above their surfaces, making Pluto-Charon a binary system. Two much smaller moons, Nix and Hydra, orbit Pluto and Charon.
Pluto lies in the resonant belt, having a 3:2 resonance with Neptune (it orbits twice round the Sun for every three Neptunian orbits). Kuiper belt objects which share this orbit are called Plutinos
Moon
The Moon is Earth's only natural satellite. It has no formal English name other than "the Moon", although it is occasionally called Luna (Latin for "moon") to distinguish it from the generic term "moon" (referring to any of the various natural satellites of other planets). Its symbol is a crescent (☽). The related adjective for the Moon is lunar (from the Latin root), but this is not found in combination with words using the prefix seleno- or suffix -selene (from the Greek deity Selene).
The average distance from the Earth to the Moon is 384,403 kilometres (238,857 miles), which is about 30 times the diameter of the Earth. The Moon has a diameter of 3,474 kilometres (2,159 miles)[1] – about one-third that of the Earth. It is the fifth largest moon in the Solar System behind Ganymede, Titan, Callisto, and Io. The Moon makes one complete orbit about the Earth every 27.3 days, and the periodic variations in the geometry of the Earth-Moon-Sun system are responsible for the lunar phases that repeat every 29.5 days. The gravitational attraction of the Moon is largely responsible for the tides on Earth (with a secondary contribution from the Sun).
The Moon is the only celestial body that human beings have orbited or landed on. The first man-made object to escape Earth's gravity and pass near the Moon was the Soviet Union's Luna 1, the first man-made object to impact the lunar surface was Luna 2, and the first photographs of the normally occluded far side of the Moon were made by Luna 3, all in 1959. The first spacecraft to perform a successful lunar soft landing was Luna 9 and the first unmanned vehicle to orbit the Moon was Luna 10, both in 1966.[1] The United States' Apollo program achieved the first (and only) manned missions to the Moon, culminating in 6 landings between 1969 and 1972.
Manned exploration of the Moon ceased with the conclusion of the Apollo program, although several countries have recently announced plans to send either manned or unmanned spacecraft to the Moon in the near future. On 4 December, 2006, NASA outlined plans for a permanent base on the Moon as part of preparation for a voyage to Mars. Construction of the base is scheduled to take approximately five years, with the first preliminary missions beginning by 2020.[2]
Sun
The Sun is the star at the center of the Solar System. The Earth and other matter (including other planets, asteroids, meteoroids, comets and dust) orbit the Sun, which by itself accounts for about 99.8% of the solar system's mass. Energy from the Sun—in the form of sunlight—supports almost all life on Earth via photosynthesis, and drives the Earth's climate and weather.
Its too much for a little girl like u ,but u can use it anyway.