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The Solar System is the collection of astronomical objects that are within the gravitational influence of the star called the Sun. The Solar System is located in the Milky Way galaxy, in the inner rim of the Orion-Cygnus arm of said galaxy. In the Solar System contains 13 known planets, 8 known major planets and 5 known dwarf planets. Of the 8 known major planets, four of them are terrestrial planets (Mercury, Venus, Earth, and Mars). The other four known major planets are giant planets, which can be again divided into gas giant planets (Jupiter and Saturn) and ice giant planets (Uranus and Neptune). Out of all of these planets, Earth is the only one known with confirmed life and is the homeworld of humanity.
Formation[]
The Solar System formed approximately 4.6 billion years ago when a molecular cloud of gas and dust coalesced into many other stars; one of these stars being the Sun. Over time, as the Sun formed, a protoplanetary disk emerged to orbit the Sun, which later coalesced into the planets and other objects. Closer to the Sun, only high boiling point materials like iron and rock could exist in the condensed form, giving the rise of terrestrial planets orbiting close to the Sun, including the Earth. Farther away from the Sun, beyond the solar frost line, it was cold enough for volatile materials to exist in the condensed form, and so is the place where the giant planets formed, orbiting the Sun at a much farther distance. The preceding nebula in which the Sun formed in had only a small fraction of high boiling point materials, since volatile materials were more plentiful, which is the reason why the giant planets are much bigger than the terrestrial planets.
The star PDS 70 is a very young pre-main sequence star that has a protoplanetary disk with planets forming inside it. This could have been how the Sun and the Solar System formed. Credit: ESO/A. Müller et al, VLT
Because of a protoplanetary disk's almost always nature to rotate in the same direction as it's star's rotation, all of the planets and most other astronomical objects gravitationally bound to the Sun orbit the Sun in the same direction as the Sun's axial rotation. Similar to this, large or small moons orbiting the planets of the Solar System also orbit their respective planet in the same manner, because the planets themselves had or have disks of their own, called circumplanetary disks. There are exceptions tho however.
About the Solar System[]
The Sun[]
The Sun in true color. Unlike how humanity sees the Sun from Earth during a sunrise or sunset, the Sun is actually almost pure white in color to the human eye. Credit: Matúš Motlo
The Sun (⨀) is, of course, the star at the center of the Solar System, in which all of the planets and other astronomical objects of it orbit. It is a typical and relatively common type of star known as a yellow dwarf star; more specifically, it is a type of star known as a G-type main sequence star of spectral type G2V according to the Morgan-Keenan stellar classification scheme made by humanity. The "G2" means that it has an average surface temperature of approximately 5800 Kelvin and the "V" means that it is a main sequence star currently fusing hydrogen into helium in it's core through nuclear fusion; the most common stage that a star is in.
The Sun as seen in the software SpaceEngine. Notice it's very active stellar corona. Credit: Cosmographic Software
Despite being a relatively insignificant star in the universe, the Sun holds a special place to life on the terrestrial planet Earth, as almost all life on Earth depend on the Sun's heat and radiation output to sustain itself. Although it is a life-bearing star, the Sun still emits things that could be considered harmful to life on Earth, like for example ionizing radiation in the form of ultraviolet radiation and it's stellar wind. The way as to how life on Earth is protected from these harmful activity of the Sun will is discussed in the Earth section.
The Planets[]
As said before, there are 8 known major planets and 5 known dwarf planets orbiting the Sun.
Terrestrial Planets[]
Mercury[]
Mercury (☿) is the first terrestrial planet from the sun, as it is only 57.91 million kilometres (35,983,605.742 miles) away from the sun. The planet was named after a Roman god Mercurius, the Roman god of commerce. Mercury's surface is blanketed in large impact craters left behind from the countless amount of asteroids that have hit the planet due to the lack of an atmosphere, meaning there is nothing to burn up these asteroids. The largest of these craters is Caloris Planitia, which is 1,550 kilometres (960 miles) in diameter. Mercury's surface has a very large rupes system. Rupes is the Latin word for cliff. The term is used in planetary geology to refer to structures on the surface of planets generated by geologic activity. Mercury is the smallest planet in the Solar System as its equatorial radius is 2,439.7 kilometres (1,516 miles). In terms of mass, Mercury is bigger than the largest moons in the Solar System, but in terms of radius, it is smaller.
Venus[]
Venus (♀) is the second terrestrial planet from the sun, as it is 108.21 million kilometres away from the sun (67,238,576.712 miles). It was named after the Roman goddess of love. Venus is sometimes called The Earth's twin because of its similar mass, diameter, gravity, and density to Earth. Venus is unique from other terrestrial planets in the Solar System because of its quite thick and dense atmosphere, which is mostly made up of carbon dioxide with thick sulfuric acid clouds blanketing the planet, and because its atmosphere causes it to rotate the opposite direction of the way it orbits the sun. This is because of the currents of its atmosphere. It takes Venus 224.7 days to complete an orbit around the sun. Venus's average surface temperature is 464 ℃ (867 ℉) and a pressure 92 times Earth's pressure at sea level. These pressures cause carbon dioxide to get compressed into a supercritical state, essentially turning it to an ocean on Venus. Venus is separated into a core, mantle, and crust like The Earth. Venus doesn't have any plate tectonics because internal heat escapes through volcanism, which causes resurfacing instead of plate tectonics.
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Earth, our home. Credit: Ron Evans/Harrison Schmitt
The Earth (♁) is the third terrestrial planet from the sun, and the planet that humanity and every other species of animal inhabits. Its tectonic plates can create earthquakes, mountain ranges, and volcanoes. The Earth is an ocean world with 70.8% of its surface (360,000,000 square kilometres) covered in water. Earth is 149,598,023 kilometres (92,955,901.908 miles) away from the sun. Earth is the only object in the Solar System that is confirmed to have life, and it may be the only one. It harbors many interesting types of lifeforms that are unique to it, and the first of these was simple single celled bacteria that developed on earth or was brought by an asteroid or Theia 4 billion years ago. Its liquid outer core generates a magnetic field that deflects most of the solar wind and cosmic rays that threaten to destroy The Earth. Earth's atmosphere burns up most meteorites and prevents UV light from hitting the ground. It is very nitrogen and oxygen rich with small amounts of argon, carbon dioxide, neon, and helium and other trace amounts of gases.
Mars as seen from Earth through a telescope. Credit: Marc Lecleire
Mars
Mars (♂) is a terrestrial planet named after the Roman god of war. It is located 227,939,366 kilometres (141,634,955 miles) from the sun. Mars's surface has a rusty brown color because of iron oxide dust, which covers it's entire surface. Mars is the second smallest rocky planet in the Solar System because of its diameter of 6,799 kilometres (4,212 miles), which makes it just a bit bigger than Mercury by 1.39%. A Martian solar day is 24.5 hours long, and it takes Mars 687 days (1.88 Earth years) to orbit around the sun. Mars has usually been associated with aliens and colonisation by most pop culture, however Mars is likely going to be used as a place strictly for research like Antarctica, and it's incredibly unlikely that it has any life because it is constantly being blasted by deadly radiation, it's incredibly cold, and it lacks liquid water, which is important for life to form. Mars's surface is denoted by large sandy dunes, and rock faces and clefts sticking out of the sand. The surface of Mars has many volcanoes, the most notable of which is Olympus Mons, standing at 21 kilometres (13 miles) tall, which is equivalent to almost two and a half Mt. Everests stacked on top of each other.
Jupiter
Jupiter (♃) is a gas giant positioned 778,479,000 kilometres (483,724,424.362 miles) from the sun, about 317x the mass of Earth. Jupiter was named after the god of sky and thunder, Jove. It is denoted by the beautiful bands in its atmosphere. Its diameter is 142,800 kilometres (88,695 miles). Jupiter is a gas giant, which means that it is a small, rocky core, shrouded and completely hidden in many dense layers of clouds made up of different gasses. Jupiter's upper atmosphere is composed of hydrocarbons such as ethane, acetylene, and diacetylene, which all are formed from methane molecules that are hit with UV-light and charged particles that originate from its large magnetosphere. There is also carbon dioxide and carbon dioxide as well as a little bit of water in the upper atmosphere, brought by comets burning up in Jupiter's atmosphere. Jupiter's lower atmosphere clouds are composed of a mix of different chemicals, like ammonia, ammonium hydrosulfide, and water. In the lower atmosphere there is an ocean of hydrogen that has been compressed to the point of becoming an almost liquid. This "ocean" goes down for miles, and at the bottom is the rocky, barren core of Jupiter.
