Solar System Facts

To know exactly what we mean when we say "solar system" it is important to break it down into the two words that comprise the expression. Firstly, the term "solar" is simply a word that means "of the Sun." Secondly, a system is just a collection of objects that interact to form a whole. Thus, putting the two words together provides the following definition:

The solar system is a group of objects that interact with one another, the fundamental interaction for each object being the one it has with the Sun.

Solar System Profile

Age:4.6 Billion Years
Number of Planets:8
Number of Dwarf Planets:5
Number of Moons:181
Number of Asteroids:552,894
Number of Comets:3,083
Diameter:18.75 trillion kilometers
(11.65 trillion miles)

The Objects in Our Solar System

The planets, dwarf planets and other objects in our solar system
The planets, dwarf planets and other objects in our solar system

There are many different types of objects found in the solar system: a star, planets, moons, dwarf planets, comets, asteroids, gas, and dust. In terms of the numbers of each of these objects, our current knowledge is as follows:

In terms of mass, the Sun comprises over 99.8% of the Solar System, with the planet Jupiter accounting for most of the remaining mass.

How the objects in the Solar System interact

All objects in the Solar System orbit the Sun; that is, they move around the Sun in elliptical paths. Moreover, the orbits of these objects lie roughly in the same plane, called the ecliptic plane.

The mechanism that causes the orbit of objects in the Solar System is one of the fundamental forces in nature: gravity. While the natural tendency for objects in the Solar System is to continue in a straight line of motion, the Sun exerts a force (gravity) on each object and therefore “bends” the straight path into a curved one. Additionally, other objects in the Solar System are massive enough to exert gravitational forces significant enough to alter the orbit of smaller objects. For example, the Earth’s gravity is strong enough to keep the Moon in orbit around the Earth.

The size of the Solar System

Though it is common for most people to believe that the edge of the Solar System is that of Pluto’s orbit, this is far from the truth.

Over the course of the the 20th century scientists not only hypothesized the size of the Solar System extends to almost 2 light years – that’s 125,000 times the distance from the Sun to the Earth – but also that there are many objects beyond Pluto.

Scientist now believe that there are two major regions beyond Pluto. The first is
the Kuiper Belt, a region of asteroids similar to the asteroid belt between Mars and Jupiter, and the Oort Cloud, a spherical region that contains numerous comets.

Visit the planets or dwarf planets pages for more information or browse the various objects of the solar system by clicking the images below.

The formation of the solar system

Although there is some debate as to the Solar System’s formation, the following outline is currently the best known explanation of how the Solar System developed.

  • Approximately 4.6 billion years ago a large cloud of gas and dust was disturbed by some force. (Scientists have theorized that this force was a nearby supernova.)
  • As a result of this disturbance and the energy introduced to the cloud, the cloud began to move.
  • Once the movement began, the cloud started to collapse in on itself due to its own gravity.
  • During the process of collapsing, the cloud began to rotate and heat up.
  • As the cloud continued to collapse, the cloud’s temperature continued to rise and its rotation became faster and faster. As a result, the cloud eventually began to flatten out into a disk shape with most of the mass located at its center.
  • At some point the pressure and temperature became so great at the cloud’s center that nuclear fusion began to take place. It was then that the Sun was born.
  • After the Sun was born, the gases and dust further out from the disk’s center began to cool and condense into tiny particles.
  • As more and more particles formed they began to collide with one another and stick together, thus creating particles as large as rocks and boulders.
  • Like the smaller particles that collided, the boulder-sized particles began to impact and join together. These larger bodies are known as planetisimals.
  • Eventually, enough planetisimals joined together to form planetary embryos. However, unlike the small particles, boulders, and planetisimals, planetary embryos were massive enough to exert significant gravitational force on surrounding objects. Hence, instead of random collisions between objects, planetary embryos pulled objects in the surrounding area to itself.
  • Once all of the material in the area of each planetary embryo was pulled in, the planets were born.
  • All other significant material in the solar system that did not join to form the Sun or the planets condensed to form the moons, asteroids, or comets.
  • Over time, the orbits of the planets and other bodies stabilized into the solar system that we know today.