User:Paul Bajande/sandbox

This topic is about the Solar System

= Solar System = The Solar System is the gravitationally bound system that includes the Sun and its orbiting objects. The Solar System was created by the gravitational collapse of a massive interstellar molecular cloud 4.6 billion years ago. The Sun contains 99.86 percent of the mass of the system, with Jupiter holding the majority of the remaining mass. Mercury, Venus, Earth, and Mars, the four inner system planets, are terrestrial planets made mostly of rock and metal. The outer system's four enormous planets are far larger and more massive than our own.

There are an unknown number of smaller dwarf planets and numerous minor Solar System bodies circling the Sun.[d] Natural satellites orbit six of the main planets, the six biggest potential dwarf planets, and many of the smaller worlds, which are referred to as "moons" after the Moon. Jupiter's moon Ganymede and Saturn's moon Titan are both bigger than Mercury, the smallest terrestrial planet, although not more massive, while Jupiter's moon Calisto is almost as huge. Planetary rings of ice, dust, and moonlets surround each of the main planets and certain smaller things. The asteroid belt, which sits between Mars and Jupiter's orbits, is made up of objects made of rock, metal, and ice. The Kuiper belt and dispersed disc reside beyond Neptune's orbit.

Mercury
is the closest planet to the Sun. The smallest planet in the Solar System (0.055 M Earth), Mercury has no natural satellites. The dominant geological features are impact craters or basins with ejecta blankets, the remains of early volcanic activity including magma flows, and lobed ridges or rupes that were probably produced by a period of contraction early in the planet's history. Mercury's very tenuous atmosphere consists of solar-wind particles trapped by Mercury's magnetic field, as well as atoms blasted off its surface by the solar wind. 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, or that it was prevented from fully accreting by the young Sun's energy.

Venus
Venus (0.7 AU (100 million km; 65 million mi) from the Sun) is close in size to Earth (0.815 M Earth) and, like Earth, has a thick silicate mantle around an iron core, a substantial atmosphere, and evidence of internal geological activity. 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 (752 °F), mainly due to the amount of greenhouse gases in the atmosphere. The planet has no magnetic field that would prevent depletion of its substantial atmosphere, which suggests that its atmosphere is being replenished by volcanic eruptions. A relatively young planetary surface displays extensive evidence of volcanic activity, but is devoid of plate tectonics. It may undergo resurfacing episodes on a time scale of 700 million years.

Earth
Earth (1 AU (150 million km; 93 million mi) from the Sun) is the largest and densest of the inner planets, the only one known to have current geological activity, and the only place where life is known to exist. Its liquid hydrosphere is unique among the terrestrial planets, and it is the only planet where plate tectonics has been observed. Earth's atmosphere is radically different from those of the other planets, having been altered by the presence of life to contain 21% free oxygen. The planetary magnetosphere shields the surface from solar and cosmic radiation, limiting atmospheric stripping and maintaining habitability. It has one natural satellite, the Moon, the only large satellite of a terrestrial planet in the Solar System.

Mars
Mars (1.5 AU (220 million km; 140 million mi) from the Sun) is smaller than Earth and Venus (0.107 M Earth). It has an atmosphere of mostly carbon dioxide with a surface pressure of 6.1 millibars (0.088 psi; 0.18 inHg); roughly 0.6% of that of Earth but sufficient to support weather phenomena. Its surface, peppered with volcanoes, such as Olympus Mons, and rift valleys, such as Valles Marineris, shows geological activity that may have persisted until as recently as 2 million years ago. Its red colour comes from iron oxide (rust) in its soil. Mars has two tiny natural satellites (Deimos and Phobos) thought to be either captured asteroids, or ejected debris from a massive impact early in Mars's history.