Solar System

## General Information

The Sun and its orbiting objects form the Solar System, which is a gravitationally bound system. The biggest of these objects make up a planetary system that consists of eight planets, numbered from the Sun in the following order: four giant planets, Jupiter and Saturn, two gas giants, Uranus and Neptune, and four terrestrial planets, Mercury, Venus, Earth, and Mars. The majority of the material on the terrestrial planets, which have distinct surfaces, is metal and rock. Whereas the ice giants are mostly composed of volatile materials like water, ammonia, and methane, the gas giants are primarily composed of hydrogen and helium. These terrestrial and massive planets are referred to as the inner and outer solar systems, respectively, in certain sources.

A massive interstellar molecular cloud collapsed due to gravity 4.6 billion years ago, creating the Solar System. The cloud eventually gave rise to the Sun and a protoplanetary disk, which later combined to create planets and other objects. This explains why the orbits of all eight planets are close to the same plane. Currently, the Sun contains 99.86% of the mass of the Solar System, with Jupiter holding the majority of the remaining mass. Natural satellites or moons orbit around six planets and numerous more bodies. Planetary rings, made of ice, dust, and occasionally moonlets, surround all big planets and a few smaller ones.

Numerous minor bodies and smaller dwarf planets orbit the Sun; the exact number is unknown. These objects can be found in the Kuiper belt, the asteroid belt between Mars and Jupiter's orbits, the dispersed disc beyond Neptune's orbit, and even further out in the Solar System (where they would be categorized as extreme trans-Neptunian objects). Astronomers generally agree that the asteroid Ceres, the scattered-disc objects Gonggong, Eris, and Sedna, and the Kuiper-belt objects Pluto, Orcus, Haumea, Quaoar, and Makemake are all nine dwarf planets. Comets, centaurs, and interplanetary dust storms are just a few of the many small-body populations that freely move around the Solar System.

The heliosphere is an area that resembles a bubble and is created by the solar wind, which is a stream of charged particles that emanates from the Sun. The heliopause, which reaches the edge of the dispersed disc, is the point where the pressure from the solar wind and the opposing pressure of the interstellar medium are equal. It is also possible that the Oort cloud, which is assumed to be the parent cloud of long-period comets, exists at a distance around a thousand times greater than that of the heliosphere. The end of the Solar System is located beyond them. The Milky Way includes the Solar System, and Proxima Centauri, which is 4.24 light-years distant, is the star nearest to the Solar System.

### History

#### Formation

When a section of a massive molecular cloud collapsed under the force of gravity, the Solar System was created 4.568 billion years ago. This original cloud probably produced multiple stars and was several light-years wide. This molecular cloud, like other molecular clouds, was mostly composed of hydrogen, with trace quantities of helium and heavier elements that had been fused by earlier star generations. The pre-solar nebula, which was the area that would eventually form the Solar System, rotated more quickly as a result of conservation of angular momentum throughout its collapse.

The majority of the mass gathered in the center, which grew hotter than the surrounding disk. The shrinking nebula flattened into a protoplanetary disk with a hot, dense protostar at its core and a diameter of around 200 AU as its rotation accelerated. The planets were created via accretion from this disc, where gas and dust were drawn to one another by gravity and combined to form ever-larger entities. In the early Solar System, there may have been hundreds of protoplanets; however, they either combined, were destroyed, or were expelled, leaving the planets, dwarf planets, and other small bodies.

Mercury, Venus, Earth, and Mars are rocky planets that formed in the heated inner Solar System near the Sun solely because metals and silicates have higher boiling temperatures than other substances. The terrestrial planets were limited in size because metallic elements made up a relatively minor portion of the solar nebula. The frost line, the area between Mars and Jupiter's orbits where material is sufficiently cool for volatile ice compounds to stay solid, is where the big planets—Jupiter, Saturn, Uranus, and Neptune—formed.

These planets were able to expand to a big enough size to absorb enormous atmospheres of the lightest and most abundant elements, helium and hydrogen, since the ices that produced them were more common than the metals and silicates that built the terrestrial inner planets. Asteroid belts, Kuiper belts, and Oort cloud are examples of locations where leftover material that never became planets gathered. The formation of these areas and the possibility that the outer planets formed in different locations and moved to their present orbits due to a variety of gravitational interactions are explained by the Nice model.

The protostar's core hydrogen density and pressure increased to the point where thermonuclear fusion might start in less than 50 million years. The temperature, response rate, density, and pressure all grew until the thermal pressure balanced the gravitational force, achieving hydrostatic equilibrium. The Sun changed into a main-sequence star at this time. The Sun's main-sequence phase will span around 10 billion years from start to finish, whereas the total duration of all other following stages of the Sun's pre-remnant existence will be roughly two billion years. The heliosphere was formed by the Sun's solar wind, which also carried the remnant gas and dust from the protoplanetary disk into interstellar space.

Until all of the hydrogen in the Sun's core has been converted to helium, which will happen in around 5 billion years, the Solar System will essentially remain as it is now. The Sun's main sequence life will finish at this point. When that happens, the Sun's core will compress, causing hydrogen to fuse along a shell that encircles the inert helium. This will result in a higher energy output than it does now. The Sun will turn into a red giant when its outer layers enlarge to almost 260 times their current diameter. The Sun's surface will be colder than it is on the main sequence due to its larger surface area.

It is predicted that the Sun will continue to grow, vaporizing Venus and Mercury and making Earth uninhabitable. The Sun will burn helium for a small portion of the time it burnt hydrogen in the core when the core temperature rises to a point where helium fusion is possible. The Sun's bulk prevents it from initiating the fusion of heavier elements, and nuclear processes within its core will eventually diminish. Its outer layers will burst out into space, revealing a dense white dwarf that is just slightly larger than Earth but has half the mass of the Sun.The outer layers that are expelled will create a planetary nebula, which will replenish the interstellar medium with part of the material that originally produced the Sun but is now enhanced with heavier elements like carbon.

### Properties

#### Orbit

The ecliptic, or plane of Earth's orbit, is where the planets and other massive objects in orbit around the Sun are located. Comets and other smaller ice objects usually orbit this plane at much larger angles. Natural satellites known as moons circle the majority of the planets in the Solar System, giving rise to secondary systems of their own. With one face always facing their parent, many of the biggest natural satellites rotate in synchrony. Planetary rings are slender bands of microscopic particles that circle the four massive planets in tandem.

The majority of other objects, including planets, circle the Sun in the same direction that it rotates due to the development of the Solar System. In other words, looking at it from above the north pole of Earth, counter-clockwise. Certain exceptions exist, like Halley's Comet. The majority of the bigger moons follow the planetary rotation and orbit their planets in a prograde direction; the biggest moon, Triton, orbits Neptune's planet in a retrograde direction. With the exception of Venus, most bigger objects revolve about their own axes in a prograde direction with respect to their orbit.

Kepler's rules of planetary motion, to a decent first approximation, define how objects circle the Sun. The body's annual distance from the Sun varies because these principles dictate that every object moves in an ellipse, with the Sun at one point. The term "perihelion" refers to a body's closest point to the Sun, while "aphelion" denotes its farthest point from the Sun. The orbits of all the planets, except Mercury, are almost exactly round, while those of numerous comets, asteroids, and objects in the Kuiper belt have extremely elliptical paths. Kepler's rules do not take into consideration the gravitational attraction that various bodies have on one another; rather, they simply explain how the gravity of the Sun affects an orbiting body.

The entire quantity of rotational and orbital momentum that each of the Solar System's moving parts possesses is known as its angular momentum. Despite being the system's mass dominant, the Sun only contributes around 2% of the angular momentum. With comets potentially making a sizable contribution, the planets—Jupiter foremost among them—account for the majority of the remaining angular momentum as a result of their mass, orbit, and separation from the Sun.

#### Composition

The Sun, four smaller inner planets encircled by a belt of primarily stony asteroids, and four massive planets encircled by the Kuiper belt of predominantly frozen objects make up the basic structure of the Solar System as it is now shown on chart. This structure is often arbitrarily divided into distinct sections by astronomers. The asteroid belt and the four terrestrial planets make up the inner Solar System. Beyond the asteroids are the four major planets and the furthest reaches of the Solar System. Ever since the Kuiper belt was discovered, the objects beyond Neptune are regarded as belonging to a separate area in the farthest sections of the Solar System.

This low-mass star, which makes up 99.86% of the known mass of the Solar System and dominates it gravitationally, is the main constituent of the system. 99% of the remaining mass of the Sun is made up of its four biggest circling components, the giant planets, of which Jupiter and Saturn combined make up more than 90%. Together, the remaining objects in the Solar System—which include the comet, asteroids, moons, four terrestrial planets, dwarf planets, and comets—make up less than 0.002% of the system's total mass.

Like Jupiter and Saturn, the Sun is mostly made of hydrogen and helium (around 98%). Since the early Sun produced heat and light pressure, there is a composition gradient in the Solar System; elements with high melting points make up objects closer to the Sun, which are more impacted by these forces. The majority of the materials that make up objects farther from the Sun have lower melting points. The frost line, which is located around five times Earth's distance from the Sun, is the limit of the Solar System beyond which those volatile materials may congregate.

Rocks like silicates, iron, and nickel make up the majority of the objects in the inner Solar System. The primary constituents of Jupiter and Saturn are gases like neon, helium, and hydrogen that have enormous vapor pressures and extremely low melting points. Ices may melt at temperatures as high as a few hundred kelvins, just as water, methane, ammonia, hydrogen sulfide, and carbon dioxide. They are distributed throughout the Solar System as gases, liquids, and ices. Sleek materials make up most of the large planets' satellites, much of Neptune and Uranus (the "ice giants"), and a plethora of minor objects outside of Neptune's orbit. Volatiles are defined as gasses and ices together.

#### Distance

If a planet's orbit were exactly round, the distance from Earth to the Sun would equal the astronomical unit. The Sun's radius, for instance, is 0.0047 AU. Because of this, the volume of the Earth is around one millionth (10−6) that of the Sun, whereas the volume of a sphere with a radius equal to the size of Earth's orbit is 0.00001% that of the Sun. Neptune, the planet with the greatest distance from the Sun, is 30 AU, whereas Jupiter, the biggest planet, is 5.2 AU away with a radius of 71,000 km.

With very few exceptions, the orbit of the next closest object to the Sun is greater than the orbit of a planet or belt the more away it is from the Sun. Venus is around 0.33 AU farther from the Sun than Mercury, for example, whereas Saturn is 4.3 AU away from Jupiter and Neptune is 10.5 AU away from Uranus. The Titius–Bode rule and Johannes Kepler's model, which is based on the Platonic solids, are two examples of attempts to establish a link between these orbital distances, however current research has disproved both theories.

#### Environment

The heliosphere, which covers a large portion of the solar planetary system, is the outermost layer of the solar atmosphere. The solar wind, which the Sun continuously emits along with light, is a stream of charged particles. Between 900,000 and 2,880,000 kilometers per hour, this stream of particles expands outward and fills the space between the Solar System's components. The ultimate consequence is the interplanetary medium, a thin, dusty atmosphere that reaches at least 100 astronomical units (AU). Large objects are still gravitationally tethered to the sun beyond the heliosphere, but the distribution of micro-scale particles is homogenized by the flow of matter in the interstellar medium.

There are at least two disc-like areas of cosmic dust in the interplanetary medium. The first is the source of the zodiacal light; it is the zodiacal dust cloud, which is located in the inner Solar System. A relatively recent theory suggests that the planet Mars is its genesis. It may have developed by collisions inside the asteroid belt caused by gravitational interactions with the planets. The second dust cloud, which ranges in size from 10 to 40 astronomical units, was most likely produced by Kuiper belt impacts.

Space weather and geomagnetic storms are produced when the heliosphere is disturbed by surface activity on the Sun, such as solar flares and coronal mass ejections. Massive amounts of material and a magnetic field are blasted off the Sun's surface by coronal mass ejections and related phenomena. When charged particles are drawn into Earth's upper atmosphere by the interaction of this material's magnetic field with Earth's magnetic field, aurorae can be observed close to the magnetic poles. The Sun's revolving magnetic field acts on the interplanetary medium to generate the spiral-shaped heliospheric current sheet, the biggest stable structure inside the heliosphere.

#### Planets

* Mercury
* Venus
* Earth
* Mars
* Jupiter
* Saturn
* Uranus
* Neptune

#### Dwarf planets

##### Asteroid Belt

Asteroids are categorized as minor Solar System bodies, with the exception of Ceres, the biggest. They are mostly made of refractory, stony, and metallic materials that are carbonaceous, along with some ice. Their sizes vary from a few meters to hundreds of kilometers. The precise distinction between meteoroids and micrometeoroids—two terms used to describe asteroids smaller than one meter—has been disputed throughout time. As of 2017, the IAU refers to smaller particles as "dust" and classifies asteroids with a diameter of between about 30 micrometers and one meter as micrometeoroids.

Between 2.3 and 3.3 AU from the Sun, the asteroid belt is located in the orbit between Mars and Jupiter. It is believed to be pieces of the Solar System's original composition that Jupiter's gravitational pull prevented from forming. Tens of thousands, if not millions, of objects larger than one kilometer can be found in the asteroid belt. In spite of this, it is improbable that the asteroid belt's overall mass exceeds a thousandth of Earth's. Because of the asteroid belt's extreme sparsity, spacecraft frequently travel through it unharmed.

* Ceres

##### Kuiper Belt

The Kuiper belt is a massive ring of debris that resembles the asteroid belt but is mostly made up of ice particles. Its distance from the Sun is between 30 and 50 AU. Though some of the biggest ones are likely big enough to qualify as dwarf planets, it is primarily made up of tiny things from the Solar System. Though the overall mass of the Kuiper belt is believed to be about a tenth or possibly a hundredth of Earth's mass, there are approximately 100,000 objects in the band with a diameter more than fifty kilometers, according to estimates. The majority of the satellites orbiting several Kuiper belt objects have a significant inclination of around 10° towards the ecliptic plane.

Resonant trans-Neptunian objects and the "classical" belt comprise the bulk of the Kuiper belt. These orbits have periods that are just a multiple of Neptune's; for instance, they round the Sun two times for every three times that Neptune does, or once every two. The classical belt, which spans around 39.4 to 47.7 AU, is made up of objects that are not in resonance with Neptune. Some members of the classical Kuiper belt are referred to as "cubewanos" in honor of the earliest known instance of them, 1992 QB1, and are still in low-eccentricity, near-primordial orbits.

* Haumea
* Makemake
* Eris
* Pluto
* 90377 Sedna
* 50000 Quaoar
* 90482 Orcus
* 225088 Gonggong
* 10 Hygiea
* 704 Interamnia
* 2060 Chiron
* 2017 FO161

#### Moons

##### Mars

* Phobos
* Deimos

##### Jupiter

* Europa
* Ganymede
* Io
* Callisto
* Amalthea
* Himalia
* Carme
* Valetudo
* Adastrea
* Thebe
* Pasiphae
* Ananke
* Elara
* Sinope
* Lysithea
* S/2003 J 2
* S/2003 J 12
* Calirrhoe
* Themisto
* Kalyke
* Eupheme
* Arche
* Cylenne
* Chaldene
* S/2003 J 4
* S/2003 J 9
* S/2003 J 10
* S/2003 J 16
* Eirene
* Eukelade
* Iocaste
* Hegemone
* Aoede
* Helike
* Harpalyke
* Herse
* Autonoe
* Erinome
* Jupiter LXI
* Philophrosyne
* Isonoe
* Hermippe
* Aitne
* Euporie
* Euanthe
* Eurydome
* Megaclite
* Metis
* Jupiter LXII
* Thyone

##### Saturn

* Titan
* Enceladus
* Mimas
* Iapetus
* Dione
* Tethys
* Pan
* Rhea
* Epimetheus
* Hyperion
* Phoebe
* Daphnis
* Pallene
* Narvi
* Janus
* Erriapus
* Ijiraq
* Kiviuq
* Telesto
* Methone
* Pandora
* Paaliaq
* Albiorix
* Mundilfari
* Bebhionn
* Hati
* Aegaeon
* Anthe
* Ymir
* Fenrir
* Bestla
* Polydeuces
* Fornjot
* Aegir
* Hyrrokkin
* Loge
* Jarnsaxa
* Farbauti
* Bergelmir
* Tarvos
* Siarnaq
* Skathi
* Thrymr
* Suttungr
* Prometheus
* Atlas
* Calypso
* S/2006 S 1
* Greip
* S/2007 S 2
* Saturn LVIII

##### Uranus

* Umbriel
* Titania
* Oberon
* Miranda
* Ariel
* Puck
* Cressida
* Desdemona
* Perdita
* Setebos
* Trinculo
* Stephano
* Sycorax
* Ophelia
* Cordelia
* Mab
* Caliban
* Prospero
* Cupid
* Rosalind
* Portia
* Bianca
* Juliet
* Belinda
* Margaret
* Francisco
* Ferdinand

##### Neptune

* Triton
* Hippocamp
* Proteus
* Nereid
* Thalassa
* Despina
* Galatea
* Neso
* Psamathe
* Halimede
* Laomedeia
* Naiad
* Larissa
* Sao

##### Haumea

* Namaka
* Hi'iaka

##### Pluto

* Charon
* Kerberos
* Nix
* Hydra
* Stix

##### Comets

Comets are tiny entities in the Solar System that are mostly made of volatile ices. They are usually only a few kilometers wide. Their orbits are very eccentric, with an aphelion that is well beyond Pluto and a perihelion that is often inside the orbits of the inner planets. A comet's ice surface sublimates and ionizes as it approaches the Sun as it enters the inner Solar System, producing a coma—a lengthy tail of gas and dust that is frequently visible to the unaided eye.

Comets with short periods have orbits that are less than 200 years. The orbits of long-period comets span thousands of years. It is believed that comets with short periods originate in the Kuiper belt, while comets with long periods, like Hale-Bopp, are believed to originate in the Oort cloud. A single parent's split led to the formation of several comet groupings, such the Kreutz sungrazers. It's hard to pinpoint the exact orbits of comets that have hyperbolic orbits, however some comets may have formed outside of our solar system. Asteroids are frequently used to describe ancient comets whose volatiles have mainly been driven out by solar heat.

## Gallery

The first solar system, seen in "The Solar System -- our home in space"A point of view of the solar system from an alien in the Asteroid Belt.