Solar System

True color of the Sun

**Sol,** or also known as **Solar System**, is the capital system and the prime administrative sector of the Galactic Confederation, a major political entity located within the Milky Way. The current population of the Solar System is estimated to be around 150 billion individuals, and is composed of many races, including humans, androids, and intragalatic species.

The Solar System is the assembly of the Sun and the objects that encircle it, coupled by gravity. This arrangement was created around 4.6 billion years ago in a gigantic interstellar cloud of gas. The Sun holds the majority of the system's mass (99.86%) while Jupiter holds the rest. The four inner planets, Mercury, Venus, Earth and Mars, are made up mostly of rock and metal. The four outer planets, Jupiter, Saturn, Uranus and Neptune, are significantly greater and heavier than the inner planets. Two of these, Jupiter and Saturn, are gas giants composed principally of hydrogen and helium, whereas the two others, Uranus and Neptune, are ice giants with their main components being substances with higher melting points than hydrogen and helium, such as water, ammonia and methane. All eight planets revolve in nearly circular trajectories close to the plane of Earth's orbit, known as the ecliptic.

## Formation

The formation of the Solar System began 4.6 billion years ago with a giant molecular cloud composed mostly of hydrogen and helium. This interstellar cloud was disturbed by a shock wave, likely caused by an exploding star in a nearby supernova event, which triggered its collapse. As it collapsed, it spun faster and flattened into what is known as a protoplanetary disk—a rotating disc of gas and dust particles from which planets would eventually form. Over time, gravity pulled clumps together to form larger bodies called planetesimals that collided with each other to create even bigger objects called **protoplanets**. These collisions also released energy that heated up the material within them until they became hot enough for nuclear fusion to occur in their cores—the process that powers stars like our Sun today. The leftover material then formed asteroids, comets and other small bodies orbiting around these newly-formed planets.

Over millions of years, this process continued until all eight planets were formed along with their moons and rings; dwarf planets such as Pluto; asteroids; comets; interplanetary dust particles; and many other small objects orbiting around them in nearly circular trajectories close to the ecliptic plane (Earth's orbital path). In addition to forming new objects, the collisions between planetesimals and protoplanets also caused some of them to be ejected from the Solar System or destroyed. This process is still ongoing today as new objects are constantly being formed and destroyed in our ever-changing system.

## Structure

The **Sun** is the center of our Solar System and contains **99.86%** of its total mass. It is a medium-sized star composed mostly of hydrogen (74%) and helium (24%), with trace amounts of other elements such as oxygen, carbon, neon and iron. The Sun's core temperature reaches up to **15 million degrees Celsius**, which allows it to produce energy through nuclear fusion reactions that convert hydrogen into helium. This energy radiates outward in all directions from the Sun's surface in what we call sunlight—the source of light and heat for all life on Earth.

The planets are divided into two categories: inner planets (**Mercury**, **Venus**, **Earth** and **Mars**) made up mostly of rock and metal; and outer planets (**Jupiter**, **Saturn**, **Uranus** and **Neptune**) composed mainly of gas or ice. All eight planets revolve around the Sun in nearly circular orbits close to the ecliptic plane at different speeds depending on their distance from it—the closer they are to the Sun, the faster they move due to its strong gravitational pull. In addition to these objects there are also dwarf planets such as Pluto; **asteroids**; **comets**; **interplanetary dust particles**; **moons orbiting some of these bodies**; **rings** surrounding some of the planets; and many other small objects.

## Environment

The Sun's atmosphere extends beyond its main part to the heliosphere, which is largely filled with a near-vacuum known as the interplanetary medium. This is where solar wind - a continuous stream of charged particles (plasma) - flows outwards at speeds ranging from **900,000 kilometres per hour** (**560,000 mph**) to **2,880,000 kilometres per hour** (**1,790,000 mph**). Activity on the Sun's surface like solar flares and coronal mass ejections can affect this heliosphere and cause space weather and geomagnetic storms. The largest structure in it is the heliospheric current sheet created by the rotating magnetic field of the Sun.

Earth has a magnetic field that helps protect its atmosphere from being stripped away by solar winds; however Venus and Mars do not have such fields so their atmospheres are gradually fading away into space. Coronal mass ejections blow material from the Sun along with a magnetic field which interacts with Earth's magnetic field to funnel charged particles into our upper atmosphere creating aurorae near our poles.

The heliosphere also shields us partially from cosmic rays coming from interstellar space while two disc-like regions of cosmic dust exist within it: one in inner Solar System causing the zodiacal light and one in outer Solar System causing the Kuiper Belt.