What is the Solar System?
The solar system is our neighborhood in space. It is a collection of planets and smaller objects, all traveling around a central star, the sun.
Click and drag on the images in this story to look around you.
The solar system is a collection of 8 planets, more than 170 moons, dwarf planets, and countless millions of comets and asteroids, all going around the sun.
The solar system is 4.6 billion years old, and is situated in one arm of the Milky Way Galaxy. On a clear night, the ribbon of stars that cuts across the sky is the Milky Way.
Accounting for 99.9% of the solar system’s mass, the sun is a vast ball of glowing hot gas. It is so big and heavy that its gravity pulls all the objects in the solar system in orbit around it.
The smallest and closest planet to the sun. Being so close to the sun, it is also the hottest.
The second planet from the sun
One million Earths could fit inside the sun. Despite its apparent proximity, in reality, it is located 90 million miles away and light from the sun takes 8 minutes to reach Earth
Mars is our neighboring planet. It has conditions that are most similar to the Earth. Mars is commonly known as the “Red Planet” due to its appearance
Jupiter is a gas giant, known for its marvelous, marbled atmosphere. The planet’s most famous feature, a gigantic storm known as the Great Red Spot, has existed since the 17th century.
Uranus is the 7th planet from the sun. Due to its distance from the Sun, it takes Uranus 84 earth-years to complete one orbit.
Another gas giant with a gorgeous ring around it is Saturn
Neptune is the farthest planet from the sun in our solar system. Due to its distance from the sun, it’s extremely cold with a mean surface temperature of -360 °F.
The Milky Way Galaxy
Our solar system is located within one of the spiral arms of the Milky Way galaxy.
The sun is optimally located in one of the outer spiral arms away from vast star clusters and potentially dangerous supernovas, resulting in a relatively stable solar system that, at least in the case of one planet, can support life.
Our solar system is located in a minor arm of the galaxy, rather than one of the 2 primary spiral arms. Our spiral arm is called Orion Arm, also known as Orion Spur.
There are an estimated 100 billion other galaxies in the observable universe. Each may consist of billions of stars, and near most stars there may be any number of planets.
Solar System Formation Part 1
For thousands of years humans were unaware of the solar system and believed that Earth was at the center of the universe.
Astronomers such as Nicolaus Copernicus, Galileo Galilei, Johannes Kepler, and Isaac Newton helped develop a new model that explained the movement of the planets with the sun at the center of the solar system.
There is no authoritative model for how the solar system was formed, but scientists have agreed on a most popular theory. They believe that the solar system evolved from a giant molecular cloud about 4.6 billion years ago.
Birth of a Star
As this dust and gas began to collapse under the weight of its own gravity, the matter contained within got squeezed tighter and tighter. At the center of the spinning cloud, a small star formed.
Solar System Formation Part 2
This star grew larger and larger as it collected more and more of the dust and gas that collapsed into it. Further away from the center of this mass where the star was forming, smaller clumps of dust and gas were also collapsing.
The star in the center eventually ignited, forming our sun, while the smaller clumps became the planets, minor planets, moons, comets, and asteroids.
Once the nuclear fusion reaction began, the sun's powerful solar winds began to blow. These winds, which are made up of atomic particles being blown outward from the sun, slowly pushed the remaining gas and dust out of the solar system.
Meanwhile, planets were forming around the sun as loose materials in space gravitated toward each other. Astronomers believe that it took millions of years for the planets to eventually form.
Asteroids and other planetesimals are “failed planets,” objects formed from the solar nebula that never got large enough to turn into planets.
Solar System Orbits
The solar system is heliocentric, meaning all solar system objects orbit the sun in a counterclockwise direction in an area called the ecliptic plane. A year describes the length it takes for a planet to complete an orbit around the sun.
Planets closer to the sun such as Mercury have shorter “years” whereas the outer planets have longer “years.” For example, it takes Neptune 164.79 Earth years to orbit the sun completely, while it takes Mercury only 88 Earth days.
An orbit is the path an object takes in space as it revolves around another object. Orbit in space is the result of gravitation pull of one large body over another.
The Inner Planets
The inner planets (Mercury, Venus, Earth, and Mars) are all relatively close together.
The Outer Planets
The outer planets (Jupiter, Saturn, Uranus, and Neptune) are much more spread out.
Need for Speed
The closer a planet is to the sun, the faster it needs to travel in order to maintain its orbit. Mercury takes 88 days to orbit the sun; Neptune takes 165 years to do the same.
Planets in the Solar System
There are 8 planets in our solar system. The 4 closest planets that orbit the sun are called the terrestrial planets, and they make up the inner planets. The other 4 are the outer planets, also known as the “gas giants.”
The Planets in Perspective
Often, graphical portrayals of planets are scaled so that the planets look similar in size. In reality, this could not be further from the truth. The sun is easily the largest object in our solar system. Here we see the planets in their actual size.
Note that the distance between the planets has been reduced, otherwise we would not be able to fit all the 8 planets in a single view.
The sun is 109 times wider than the Earth. The fact that the sun is so small in our sky shows just how far away the sun is from the Earth.
For illustration purposes, the distance between the planets has been reduced. If the distance were not reduced, Neptune wouldn’t even be in the same room as the sun.
Asteroid Belt, Kuiper Belt and the Oort Cloud
The Asteroid Belt sits between the orbits of the planets Jupiter and Mars, composed of thousands of objects too small to be considered planets. Some objects are no larger than a grain of dust, while others can be more than 100 miles across.
Farther out, near the orbit of Neptune and beyond the orbit of the minor planet Pluto, sits another belt known as the Kuiper Belt. Like the Asteroid Belt, the Kuiper Belt is also made up of objects too small to be considered planets.
The Four Largest
The 4 largest asteroids in the Asteroid Belt are Ceres, Vesta, Pallas, and Hygiea, which contain half the mass of the entire belt. There was a theory that if you combined all the asteroids they would make up the missing “Fifth” rocky planet.
The largest Kuiper Belt Objects are Pluto, Quaoar, Makemake, Haumea, Ixion, and Varuna. The ice in the Kuiper Belt dates back to the formation of the solar system. They contain clues to conditions in the early solar nebula.
Whereas the 2 other belts are like flat disks, the Oort cloud is a spherical shell of icy objects. It is located in the outermost part of the solar system.