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Solar System

A Solar System From Dust

A variety of planet types orbit the Sun in our solar system. Our system of one star and eight planets was born about 4.6 billion years ago. All of the pieces were created at the same time. But wait! It wasn't a big "POOF!" and everything was here. It took billions of years for the entire system to develop. All of the gases, dust, and pieces of the system were around at the start. Eventually a star, eight planets, some smaller dwarf planets (like Pluto), and an asteroid belt developed. There wasn't even a star when the Solar System started out.

Start With A Star

The system began as a spinning blob of gases. As the blob spun for millions and millions of years, it began to flatten. It probably looked like that shape for a flying saucer. It was a round, flattened disk with a bulge in the middle. That bulge was the beginning of the Sun. Scientists call that "baby" sun a protosun. The last step for the Sun was the magic that ignited it and caused it to shine. Do you remember that dust and gas swirling around that didn't become the Sun? The disk flattened even more and the planets began to develop.

Planets From The Pieces

Eight planets developed and now orbit the Sun. As you move away from the Sun, you will first find four planets, then a group of small asteroids, and four large Jovian planets. There are also objects called dwarf planets that include bodies such as Pluto and Charon. In the past few years, astronomers have started to discover smaller objects beyond Pluto in the Kuiper Belt. The distance from the Sun to the Earth is considered "1" (scientists call that distance an astronomical unit).The average distance to Pluto from the Sun is 39.5. The Voyager probes launched decades ago are just now reaching the outer edges of our Solar System. That edge, called the heliopause, is far beyond the orbit of Pluto.

Solids and Gases

As the planets developed, two types began to emerge. In our system, we have planets that are mainly made of rock and those that are mainly made of gases. The official names are terrestrial (rocklike) and Jovian (those with gases). Of the eight planets in our system, Mercury, Venus, Earth, and Mars are the terrestrial planets. The Jovian planets include Jupiter, Saturn, Uranus, and Neptune. The Jovian planets are all much larger and have a lower density when compared to terrestrial planets. Astronomers have recently decided that there are objects in the Universe that are larger that asteroids and comets, but smaller than real planets. These dwarf planets also orbit the Sun and include Pluto, Charon, and others discovered in the Kuiper Belt. You may also hear the term trans-Neptunian objects used to describe those distant dwarf planets.

Next Stop On Cosmos4Kids Tour
Next Page on the Solar System.
> Introduction
- Sun
- Mercury
- Venus
- Earth
- Mars
- Jupiter
- Saturn
- Uranus
- Neptune
- Pluto


Solar System Details


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First View of Solar System Tail (NASA/Goddard Video)
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Astronomy Quiz

Solar System Quiz

Keywords for Review

Kinetic Energy: The energy of an object related to the motion of the object. On a simple level, an object that is not moving has no kinetic energy. An object that is moving has some amount of kinetic energy. The more an object moves, the more kinetic energy it has. An object increases its kinetic energy if it accelerates and increases its velocity. For example, as you increase the temperature of a gas, the molecules become more energetic and the system has an overall increase in kinetic energy. Kinetic Energy=(0.5)* mass * (velocity)2

Exothermic: A chemical reaction that releases energy after the reaction is complete. The energy is usually released as heat, but it can also be released as light or sound. On a small scale, a burning candle releases light and heat because of exothermic reactions as the wax burns. On a large scale, an explosion might occur when blasting with sticks of dynamite (TNT).

Activation Energy: The least amount of energy needed for a chemical reaction to occur. Reactions often require some amount of energy to get moving. For example, placing hydrogen and oxygen gases in a container will not give you water. There is a certain amount of energy required to get the first reaction going. Catalysts are substances that help to lower activation energies so that reactions can proceed.

Viscosity: A term used to measure the fluidity of a liquid. As the attractions between the molecules increase, viscosity increases. Fluids with high viscosities don’t flow easily. Some substances such as honey or sap are very slow moving and have high viscosities. Other fluids such as water or mercury (Hg) have very low viscosities.

Volatile: Volatility is the likelihood that a substance will vaporize (become a gas). Volatility measurements are all about comparing two substances. Substances with a higher vapor pressure are more volatile. Alcohol is more volatile than water because it evaporates at a lower temperature.

Reference Materials

Encyclopædia Britannica:

- Cosmos4Kids: Sun
- Chem4Kids: Matter
- Chem4Kids: Astrochemistry
- Chem4Kids: Elements
- Geography4Kids: Earth Energy
- Geography4Kids: Earth Structure
- Geography4Kids: Solar Radiation
- Physics4Kids: Gravity
- Physics4Kids: Acceleration
- Physics4Kids: Magnetic Fields
- Physics4Kids: Light

- NASA: Home Page
- NASA: Kids Home Page
- ESA: Home Page
- ESA: Kids Home Page

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