Solar System

The Sun is a huge star. It sits in the middle.

Most of the weight in our system is in the Sun. Eight planets move around it.

Four planets are rocky and close to the Sun. These are Mercury, Venus, Earth, and Mars. Four more are giant planets made of gas and ice. They live far away.

Many moons also spin around these big planets. Small rocks like asteroids float in space too. It is a very busy place!

The Solar System is a family of objects held by gravity.

The Sun sits at the center. It holds 99.86% of all the mass. This means the Sun is almost everything in our system. Inside the Sun, hydrogen turns into helium. This process, called fusion, lets out huge power.

Eight planets orbit the Sun. The four inner planets are rocky. They are Mercury, Venus, Earth, and Mars. Earth and Mars sit in the habitable zone. This is a place where sunlight can keep water liquid. The four outer planets are giants. Jupiter and Saturn are gas giants. Uranus and Neptune are ice giants.

Many other things orbit the Sun too. Dwarf planets like Pluto are small. They do not own their own orbits. Small rocks like asteroids live in a belt between Mars and Jupiter.

Some objects are moons. They orbit planets instead of the Sun. Far away, the Oort cloud holds many icy objects. This marks the outer edge of our home.

The Solar System is a huge family of objects held together by gravity.

Everything in this system orbits around the Sun. The Sun is a massive star that holds 99.86% of all the mass in the system. This means the Sun is almost everything there is. Inside its core, a process called fusion happens. In this process, hydrogen turns into helium. This releases the energy that makes the Sun shine.

This energy creates the heliosphere, which is a bubble around our system.

Our system formed about 4.6 billion years ago. It began when a dense part of a molecular cloud collapsed.

As this cloud collapsed, it started to spin faster. This spinning caused it to flatten into a disc shape. This disc is called a protoplanetary disc. Small bits of dust and gas began to stick together. This sticking process is called accretion. Over time, these bits grew into planets and other large bodies. Some early planets were destroyed or pushed away during this time.

There are eight main planets in our Solar System. The four inner planets are called terrestrial planets. They are Mercury, Venus, Earth, and Mars. These planets are mostly made of rock and metal. Earth and Mars sit in the habitable zone. In this zone, sunlight can keep water liquid on the surface. The four outer planets are much larger. Jupiter and Saturn are gas giants. Uranus and Neptune are ice giants.

These giants formed far past the frost line where it is cold enough for ice to stay solid.

Many other smaller things orbit the Sun as well. Dwarf planets are objects that are large but do not dominate their orbits. The International Astronomical Union lists Ceres, Pluto, Eris, Makemake, and Haumea as dwarf planets. Other objects like Orcus and Sedna are also called dwarf planets. Small rocks called asteroids live in a belt between Mars and Jupiter. Other icy objects live in the Kuiper belt or the distant Oort cloud. Many objects also orbit planets as moons.

Some moons, like Ganymede, are even larger than the planet Mercury.

Our Solar System is not alone in space. It moves through a cloud called the Local Cloud. The nearest star to us is Proxima Centauri. It is about 269,000 AU away. The Sun will stay a stable star for about 10 billion years. In about 5 billion years, the Sun will change. It will grow much larger and become a red giant.

This expansion might destroy the inner planets. Eventually, the Sun will leave behind a small, dense core called a white dwarf.

The Solar System is a gravitationally bound system of celestial bodies. It consists of the Sun and all the masses that orbit it. This includes the eight major planets and many other smaller objects. The Sun is the most important part of this system. It contains 99.86% of the total mass of the entire Solar System. Because the Sun is so massive, its gravity holds everything else in place.

Our system formed about 4.6 billion years ago. It began when a dense region of a molecular cloud collapsed. As this nebula contracted, it began to rotate faster due to the conservation of angular momentum. This spinning motion caused the material to flatten into a protoplanetary disc. At the center, a hot and dense protostar began to form. Within 50 million years, the pressure in the center became high enough for thermonuclear fusion. This is the process where hydrogen atoms fuse into helium. This reaction releases the massive amounts of energy that make the Sun shine.

The structure of the Solar System is divided into distinct regions. The inner Solar System contains the terrestrial planets. These are Mercury, Venus, Earth, and Mars. These planets are composed mostly of metals and silicates. They are relatively small because they formed inside the soot line. Heat from the early Sun prevented lighter materials from staying solid here. Beyond the frost line lies the outer Solar System. This region contains the gas giants, Jupiter and Saturn, and the ice giants, Uranus and Neptune. These massive planets formed where it was cold enough for volatile icy compounds to remain solid.

Many objects in the system do not qualify as major planets. Dwarf planets are objects with planetary mass that do not dominate their orbits. The International Astronomical Union recognizes Ceres, Pluto, Eris, Makemake, and Haumea as dwarf planets. Other objects like Orcus, Quaoar, Gonggong, and Sedna are also identified as dwarf planets. Smaller bodies include asteroids, comets, centaurs, and meteoroids. Many of these are found in the asteroid belt between Mars and Jupiter. Others reside in the Kuiper belt or the distant, theorized Oort cloud. The Oort cloud is a vast region that may extend to 227,000 AU from the Sun.

Natural satellites, or moons, are also found throughout the system. Many objects do not orbit the Sun directly but orbit larger bodies instead. These moons vary greatly in size. Some are tiny moonlets, while others are massive. For example, Jupiter's moon Ganymede and Saturn's moon Titan are larger than the planet Mercury. However, they have less mass than Mercury. The seven most massive moons in the system are larger and more massive than any dwarf planet.

The Sun's influence creates a protective bubble called the heliosphere. The solar wind, which is a stream of charged plasma particles, flows outward from the Sun. This wind creates an interplanetary medium filled with dust, gas, and cosmic rays. At about 70 to 90 AU from the Sun, the solar wind hits the interstellar medium. This boundary is known as the heliopause. The entire Solar System is currently moving through a region called the Local Cloud. Our closest neighboring star is Proxima Centauri, located 269,000 AU away.

The Solar System is currently in a stable state, but it will change in the future. The Sun's main-sequence life will last about 10 billion years. In roughly 5 billion years, the Sun will run out of hydrogen in its core. It will then expand into a red giant, growing to 260 times its current diameter.

This expansion may vaporize Mercury and Venus. It could also make Earth and Mars uninhabitable. Eventually, the Sun will eject its outer layers and leave behind a white dwarf. This is a dense core about the size of Earth. The ejected material may form a planetary nebula, returning elements to space.