Solar System

The Solar System[lower-alpha 3] is the gravitationally bound system of the Sun and the objects that orbit it. The largest of such objects are the eight planets, in order from the Sun: four terrestrial planets named Mercury, Venus, Earth and Mars, two gas giants named Jupiter and Saturn, and two ice giants named Uranus and Neptune. The terrestrial planets have a definite surface and are mostly made of rock and metal. The gas giants are mostly made of hydrogen and helium, while the ice giants are mostly made of 'volatile' substances such as water, ammonia, and methane. In some texts, these terrestrial and giant planets are called the inner Solar System and outer Solar System planets respectively.

Solar System
A true-color image of the Solar System with sizes, but not distances, to scale. The order of the planets are from right to left.
The Sun, planets, moons and dwarf planets[lower-alpha 1]
(true color, size to scale, distances not to scale)
Age4.568 billion years
System mass1.0014 solar masses[citation needed]
Nearest star
Nearest known planetary system
Proxima Centauri system (4.2441 ly)
Planetary system
Semi-major axis of outer known planet (Neptune)
30.11 AU
(4.5 bill. km; 2.8 bill. mi)
Distance to Kuiper cliff~50 AU
Stars1 (Sun)
Known planets
Known dwarf planets
Known natural satellites
Known minor planets1,199,224[lower-alpha 2][2]
Known comets4,402[lower-alpha 2][2]
Identified rounded satellites19
Orbit about Galactic Center
Invariable-to-galactic plane inclination60.19° (ecliptic)
Distance to Galactic Center27,000±1,000 ly
Orbital speed220 km/s; 136 mi/s
Orbital period225–250 myr
Star-related properties
Spectral typeG2V
Frost line≈5 AU[3]
Distance to heliopause≈120 AU
Hill sphere radius≈1–3 ly

The Solar System was formed 4.6 billion years ago from the gravitational collapse of a giant interstellar molecular cloud. Over time, the cloud formed the Sun and a protoplanetary disk that gradually coalesced to form planets and other objects. That is the reason why all eight planets have an orbit that lies near the same plane. In the present day, 99.86% of the Solar System's mass is in the Sun and most of the remaining mass is contained in the planet Jupiter. Six planets, six largest possible dwarf planets and many other bodies have natural satellites or moons orbiting around them. All giant planets and a few smaller bodies are encircled by planetary rings, composed of ice, dust and sometimes moonlets.

There are an unknown number of smaller dwarf planets and innumerable small bodies orbiting the Sun.[lower-alpha 4] These objects are distributed in the asteroid belt that lies between the orbits of Mars and Jupiter, the Kuiper belt, the scattered disc that both lies beyond Neptune's orbit and at even further reaches of the Solar System which they would be classified as an extreme trans-Neptunian object. There is consensus among astronomers to these nine objects as dwarf planets: the asteroid Ceres, the Kuiper-belt objects Pluto, Orcus, Haumea, Quaoar, and Makemake, and the scattered-disc objects Gonggong, Eris, and Sedna.[lower-alpha 4] Many small-body populations, including comets, centaurs and interplanetary dust clouds, freely travel between the regions of the Solar System.

The solar wind, a stream of charged particles flowing outwards from the Sun, creates a bubble-like region of the interplanetary medium in the interstellar medium known as the heliosphere. The heliopause is the point at which pressure from the solar wind is equal to the opposing pressure of the interstellar medium; it extends out to the edge of the scattered disc. The Oort cloud, which is thought to be the source for long-period comets, may also exist at a distance roughly a thousand times further than the heliosphere. The nearest stars to the Solar System are within the Local Bubble; the closest star is named Proxima Centauri and is at a distance of 4.2441 light-years away.

Share this article:

This article uses material from the Wikipedia article Solar System, and is written by contributors. Text is available under a CC BY-SA 4.0 International License; additional terms may apply. Images, videos and audio are available under their respective licenses.