Origins of the Solar System- The Solar Nebula Theory

There are lots of theories about the origin of our solar system. According to the presently accepted theory, our solar system is 5 billion years old.

The Solar System
The Solar System

Simple Outline of the Solar Nebula Theory

  1. Once upon a time, about 5 billion years ago, there was a very large nebula (nebula= cloud of stuff). This nebula was 25X the present size of solar system and had a temperature of about 50 K.
  2. Gravity pulled particles together. As the size increased, temperature increased. Most of the material clumped up in center, forming a proto-sun.
  3. Eddy currents formed at different distances, resulting in proto-planets
  4. Close to center, the high melting point elements formed inner planets: Mercury, Venus, Earth, and Mars, pictured below.


The Inner Terrestrial Planets
The Inner Terrestrial Planets

5. Far away, the low melting point materials formed outer planets: Jupiter, Saturn, Uranus and Neptune.

The Gas Giants, Outer Planets of Solar System
The Gas Giants, Outer Planets of Solar System

6. At a temperature of about 10 million K in the center, thermo-nuclear fusion began in sun and blew away most debris.

The Asteroid Belt

The Asteroid Belt is in orbit between Mars and Jupiter. It is very sparsly populated, and spacecraft can pass through without any problems. It contains thousands of objects, but the combined mass of these objects is smaller than the Earth's mass. The image below shows the Asteroid Belt's place among the planets.

The Inner Solar System, the Asteroid Belt
The Inner Solar System, the Asteroid Belt

The Kuiper Belt

The Kuiper belt occupies the Trans-Neptunian region, the area beyond Neptune that remains largely unexplored. It is similar to the Asteroid Belt, but its objects are mainly made of ice.

The image below shows a plot of known Kuiper belt objects in relation to the outer planets.

Out Solar System, Kuiper Belt
Out Solar System, Kuiper Belt

The Oort Cloud

There might to be more to this thing than its awesome, science-fictiony name, but if there is, we haven't found it yet. This is a hypothetical cloud of comets. Pretty cool, right? The Oort cloud is believed to be a spherical cloud that is the source of all of the long-term comets that enter the solar system. It is considered to be the "outer bounds" of the Solar System.

Only four known objects are considered to be part of the Oort Cloud. Below I've included a drawing of what the Oort Cloud is believed to look like.

The Outer Solar System, Kuiper Belt and Oort Cloud
The Outer Solar System, Kuiper Belt and Oort Cloud

All photos were taken from Wikimedia commons.

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Comments 4 comments

carcro profile image

carcro 5 years ago from Winnipeg

I find space to be the most interesting of subjects, likley because its the unknown and seemingly infinite. Anything infinite just facinates me. Thanks for sharing this very interesting hub! Voted Up and Awesome!


stephaniedas profile image

stephaniedas 5 years ago from Miami, US Author

You're right, it is fascinating. We know so little, and will never know it all. I'm glad you enjoyed this, thank you for the feedback.


lone77star profile image

lone77star 5 years ago from Cebu, Philippines

Nice article. Thanks!

When I first thought about the dark sea separating our system from the others around us, I had no idea of the nature of such things as Kuiper and Oort, but that was mid-50's science with a smattering of science fiction. It was Chesley Bonestell paintings of other planets and other star systems. We've come a long way in our understanding.


stephaniedas profile image

stephaniedas 5 years ago from Miami, US Author

We sure have come a long way since the 50s...the moon landings, using space for our everyday activities like cell phones and the internet. Someday I'll be looking back and thinking, "When I was young, Pluto was a planet...". Thanks for the great comment.

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