Solar System

There is a strong consensus among astronomers[e] that the Solar System has at least nine dwarf planets: Ceres, Orcus, Pluto, Haumea, Quaoar, Makemake, Gonggong, Eris, and Sedna.

[14] As is typical of molecular clouds, this one consisted mostly of hydrogen, with some helium, and small amounts of heavier elements fused by previous generations of stars.

[14] As the contracting nebula spun faster, it began to flatten into a protoplanetary disc with a diameter of roughly 200 AU[14][16] and a hot, dense protostar at the center.

[20][21] Due to their higher boiling points, only metals and silicates could exist in solid form in the warm inner Solar System close to the Sun (within the frost line).

[23] Following the dissipation of the protoplanetary disk, the Nice model proposes that gravitational encounters between planetisimals and the gas giants caused each to migrate into different orbits.

During this period, the grand tack hypothesis suggests that a final inward migration of Jupiter dispersed much of the asteroid belt, leading to the Late Heavy Bombardment of the inner planets.

[26][27] The Solar System remains in a relatively stable, slowly evolving state by following isolated, gravitationally bound orbits around the Sun.

At that time, the core of the Sun will contract with hydrogen fusion occurring along a shell surrounding the inert helium, and the energy output will be greater than at present.

[44] The boundary in the Solar System beyond which those volatile substances could coalesce is known as the frost line, and it lies at roughly five times the Earth's distance from the Sun.

[56][57] The planets, dominated by Jupiter, account for most of the rest of the angular momentum due to the combination of their mass, orbit, and distance from the Sun, with a possibly significant contribution from comets.

Attempts have been made to determine a relationship between these orbital distances, like the Titius–Bode law[60] and Johannes Kepler's model based on the Platonic solids,[61] but ongoing discoveries have invalidated these hypotheses.

The density of cosmic rays in the interstellar medium and the strength of the Sun's magnetic field change on very long timescales, so the level of cosmic-ray penetration in the Solar System varies, though by how much is unknown.

It has a higher abundance of elements heavier than hydrogen and helium ("metals" in astronomical parlance) than the older population II stars in the galactic bulge and halo.

[84] Activity on the Sun's surface, such as solar flares and coronal mass ejections, disturbs the heliosphere, creating space weather and causing geomagnetic storms.

[89] Composed mainly of silicates and metals,[90] the objects of the inner Solar System are relatively close to the Sun; the radius of this entire region is less than the distance between the orbits of Jupiter and Saturn.

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] Asteroids except for the largest, Ceres, are classified as small Solar System bodies and are composed mainly of carbonaceous, refractory rocky and metallic minerals, with some ice.

[91] Jupiter and Saturn are composed mainly of gases with extremely low melting points, such as hydrogen, helium, and neon,[166] hence their designation as gas giants.

[167] Uranus and Neptune are ice giants,[168] meaning they are largely composed of 'ice' in the astronomical sense (chemical compounds with melting points of up to a few hundred kelvins[166] such as water, methane, ammonia, hydrogen sulfide, and carbon dioxide.

These are former Kuiper belt and scattered disc objects (SDOs) that were gravitationally perturbed closer to the Sun by the outer planets, and are expected to become comets or be ejected out of the Solar System.

[199] Members of the classical Kuiper belt are sometimes called "cubewanos", after the first of their kind to be discovered, originally designated 1992 QB1, (and has since been named Albion); they are still in near primordial, low-eccentricity orbits.

When a comet enters the inner Solar System, its proximity to the Sun causes its icy surface to sublimate and ionise, creating a coma: a long tail of gas and dust often visible to the naked eye.

Oort cloud objects move very slowly, and can be perturbed by infrequent events, such as collisions, the gravitational effects of a passing star, or the galactic tide, the tidal force exerted by the Milky Way.

[257] The Sun's Hill sphere with respect to the galactic nucleus, the effective range of its gravitational influence, is thought to extend up to a thousand times farther and encompasses the hypothetical Oort cloud.

[263] The Local Bubble is a small superbubble compared to the neighboring wider Radcliffe Wave and Split linear structures (formerly Gould Belt), each of which are some thousands of light-years in length.

[277] If it orbited close to the center, gravitational tugs from nearby stars could perturb bodies in the Oort cloud and send many comets into the inner Solar System, producing collisions with potentially catastrophic implications for life on Earth.

[277] However, according to the controversial Shiva hypothesis, the changing position of the Solar System relative to other parts of the Milky Way could explain periodic extinction events on Earth.

Up to the Late Middle Ages–Renaissance, astronomers from Europe to India believed Earth to be stationary at the center of the universe[280] and categorically different from the divine or ethereal objects that moved through the sky.

Using a heliocentric model that improved upon Copernicus by allowing orbits to be elliptical, and the precise observational data of Tycho Brahe, Kepler produced the Rudolphine Tables, which enabled accurate computations of the positions of the then-known planets.

[292] In 1838, Friedrich Bessel successfully measured a stellar parallax, an apparent shift in the position of a star created by Earth's motion around the Sun, providing the first direct, experimental proof of heliocentrism.

Diagram of the early Solar System's protoplanetary disk , out of which Earth and other Solar System bodies formed
The current Sun compared to its peak size in the red-giant phase
Animations of the Solar System's inner planets orbiting. Each frame represents 2 days of motion.
Animations of the Solar System's outer planets orbiting. This animation is 100 times faster than the inner planet animation.
To-scale diagram of distance between planets, with the white bar showing orbital variations. The size of the planets is not to scale.
White ball of plasma
The Sun in true white color
Venus and Earth about the same size, Mars is about 0.55 times as big and Mercury is about 0.4 times as big
The four terrestrial planets Mercury , Venus , Earth and Mars
Asteroid populations depicted: near-Earth asteroids, Earth trojans, Mars trojans, main asteroid belt, Jupiter trojans, Jupiter Greeks, Jupiter Hilda's triangle
Overview of the inner Solar System up to Jupiter's orbit
The four largest asteroids: Ceres , Vesta , Pallas , Hygiea . Only Ceres and Vesta have been visited by a spacecraft and thus have a detailed picture.
Jupiter and Saturn is about 2 times bigger than Uranus and Neptune, 10 times bigger than Venus and Earth, 20 times bigger than Mars and 25 times bigger than Mercury
The outer planets Jupiter , Saturn , Uranus and Neptune , compared to the inner planets Earth, Venus, Mars, and Mercury at the bottom right
Plot of objects around the Kuiper belt and other asteroid populations. J, S, U and N denotes Jupiter, Saturn, Uranus and Neptune.
Orbit classification of Kuiper belt objects. Some clusters that is subjected to orbital resonance are marked.
The orbital eccentricities and inclinations of the scattered disc population compared to the classical and resonant Kuiper belt objects
The current orbits of Sedna , 2012 VP113 , Leleākūhonua (pink), and other very distant objects (red, brown and cyan) along with the predicted orbit of the hypothetical Planet Nine (dark blue)
Diagram of the Sun's magnetosphere and helioshealth
Comet Hale–Bopp seen in 1997
The planets, zodiacal light and meteor shower (top left of image)
An artist's impression of the Oort cloud , a region still well within the sphere of influence of the Solar System, including a depiction of the much further inside Kuiper belt (inset); the sizes of objects are over-scaled for visibility.
The Solar System (left) within the interstellar medium , with the different regions and their distances on a logarithmic scale
Diagram of the Local Interstellar Cloud , the G-Cloud and surrounding stars. As of 2022, the precise location of the Solar System in the clouds is an open question in astronomy. [ 259 ]
Diagram of the Milky Way, with galactic features and the relative position of the Solar System labeled.
The motion of 'lights' moving across the sky is the basis of the classical definition of planets: wandering stars.
Solar system diagram by Emanuel Bowen in 1747, when neither Uranus, Neptune, nor the asteroid belts had yet been discovered. Orbits of planets are to scale, but the orbits of moons and the sizes of bodies are not.
The Sun, the planets, their moons, and several trans-Neptunian objects The Sun Mercury Venus The Moon Earth Mars Phobos and Deimos Ceres The main asteroid belt Jupiter Moons of Jupiter Rings of Jupiter Saturn Moons of Saturn Rings of Saturn Uranus Moons of Uranus Rings of Uranus Neptune Moons of Neptune Rings of Neptune Pluto Moons of Pluto Haumea Moons of Haumea Makemake S/2015 (136472) 1 The Kuiper Belt Eris Dysnomia The Scattered Disc The Hills Cloud The Oort Cloud