1. 1. Stage One — Formation of the Sun
  2. 2. Stage Two — Beginning Formation of the Planetary Ring and Its Occupants
  3. 3. Stage Three — Orbital Paths Designation
  1. 4. Stage Four — Basic Stability is Obtained
  2. 5. Stage Five — The End is Near
  3. 6. Video Gallery

There are many theories as to how our solar system was created but the most widely excepted idea is known as the nebular hypothesis. The nebular hypothesis was first presented to the astronomy community in the 18th century by Emanuel Swedenborg, Immanuel Kant, and Pierre-Simon Laplace. Of course, because of recent developments and discoveries this hypothesis has been brought back to the table and challenged because of the unanswered questions involved with this theory, but for now, this is the solar systems story and we're sticking to it.

Sun's life cycleSun's life cycle /

In the book Evolution of the Solar System by Professors Hannes AlfvÃѓÂ©n and Gustaf Arrhenius' provided by NASA (National Aeronautics Space Administration), they describe theorized five stages in the evolutionary process of a solar system. These five stages begin with the formation of a sun and end with the death of a sun. It is evident that the sun is an important part of the creation of a solar system such as ours. It is well known that without the sun, there could be no life on Earth, but the sun also plays a major role in the formation of planetary systems as well. As the sun is created, its gravitational field aids in the formation of the planets as the dust and debris from the molecular cloud begin to compress together. So it is only fitting that the solar system begins and ends with the sun.

Stage One - Formation of the Sun

The Ring nebula, a nebula similar to what the Sun will becomeThe Ring nebula, a nebula similar to what the Sun will become /

Approximately 4 billion years ago, in the place where our solar system now resides, a thick molecular cloud filled with dust and debris was spurred into action by an outside source causing it to collapse in on itself and spin at an astronomical rate. It is believed that this molecular cloud actually existed for billions of years before this event occurred. Some have hypothesized that this was the result of shockwaves hitting the cloud from a nearby supernova, but in truth, the source is unknown.

The best way to describe this process is for you to envision a dense cloud placed into a galactic-sized centrifuge. As the centrifuge gains momentum, pressures within this cloud begin to increase and pull the larger portion of its contents towards the center while the lesser portions of the cloud expand outward flattening in the process. The increased pressures that pulled the dust and debris towards the center would be great enough to force these elements into a single mass spinning ball within its center. It is through this spin that gravity field is formed. In the next stage of the evolution of our solar system, the field of gravity will aid in the development of other planetary bodies within the system along with their current rotation around the sun.

At the core of this sun, a chemical reaction process occurs where the extreme pressure and temperature convert hydrogen atoms into molecules of helium. This "fusion" process basically combines 4 protons into a single "alpha" particle and energy is released. The release of this energy creates what is called stellar winds, basically hot air filled with particles and metals that are pushed outward into the solar system.

Stage Two - Beginning Formation of the Planetary Ring and Its Occupants

Artist's impression of the Solar NebulaArtist's impression of the Solar Nebula /

During the formation of the sun, and then after, as the larger portion of dust and debris are pulled towards the center the outer "arms" flatten out becoming the accretion disk. The accretion disk is basically the "nursery" for celestial objects as they are forming. It provides the womb for their creation along with the nutrients they need to form and grow. The remaining elements within the accretion disk are compressed together to form the other bodies of the solar system including the planets and moons that we know today.

The spin action of the cloud during the entire process is also the reason for the "spiral" appearance that our solar system has. This spin helps to create the orbit that they settle into along with creating their own rotation developing the gravity means to draw in more material for their formation and to capture other objects into their gravitational field as moons and satellites.

During this stage, there is a lot of chaos occurring as large chunks of rock and debris collide into one another. These large chunks of rock created from the small dust and particles from the cloud begin to mesh together forming even larger objects while the spin of the cloud help to create an individual rotation in each individual object which draws more material towards themselves.

Stage Three - Orbital Paths Designation

Formation of Planets in a Protoplanetary DiskFormation of Planets in a Protoplanetary Disk /

As objects are formed (such as the planets themselves), this is the stage where orbital paths are established. During this stage, many objects end up in the same orbital paths. These objects begin to collide with one another to either create one single larger mass with smaller debris pushed outward or to be broken apart and scattered about the "ring". It is during this process that it is believed that Earth collided with another celestial object called Theia which created our Moon which influences our tides and currents on Earth. Impact sites on planets, including Earth, show that objects were actively still bombarding planetary objects during this point though they were less frequent than in the first two stages. It is also during this stage, most likely during the end, that life began to form on Earth.

When speaking of objects colliding to create larger objects, these objects can not collide violently. In order for the objects to form a single object, the right amount of pressure must be applied and the impact would need to be "gentle" otherwise, the impact will only cause for both objects to break apart. It would almost be as if watching the objects come together in slow motion but because of their size, it would have the impact equivalency of a few tons of TNT.

Stage Four - Basic Stability is Obtained

Artist's impression of the Solar SystemArtist's impression of the Solar System /

This is the stage we are currently in where everything slows down but does not stop. The cloud that is now the accretion disk is still in a slight spin but has slowed considerably. All large bodies that were to be formed now have a defined orbital path around the sun and their own rotation. However, the formation is not completely over. Smaller body objects randomly get caught in tidal forces that remove them from their station. These objects can get caught in the gravitational pull of other objects and either get pulled into those objects or get caught in an orbital path around that object. We may experience meteor showers, asteroid impacts, or (like in 1994 with Shoemaker-Levy 9) comet collisions but the chance of any astronomical collisions are not very likely.

Many impact zones from the distant past show that there was still a lot of activity during the early part of this stage from objects colliding with Earth. One such impact was believed to have been the end of the dinosaurs. In the past few thousand years, however, there has not been an impact from any large objects such as asteroids, meteors, or comets. The larger portion of objects that have entered our atmosphere was too small and disintegrated before landfall.

The mass majority of objects that come near to Earth typically do not come within a few million miles. That is not to say that a large object will not collide with Earth in the near or distant future, but overall it is a fairly quiet time in the life cycle of our solar system. But in approximately 5 billion years, that will all change.

Stage Five - The End is Near

Rendering of a rising Red GiantRendering of a rising Red Giant /

Stage five is the declining years. Our solar system has another 5 billion or so years before this will happen. The sun will have started to burn itself out at about that time and transformed into a different planetary object. As it cools it will begin to expand engulfing any nearby planets or objects becoming a red giant. A red giant still has much of its radioactive heat but the thermal fusion has or is beginning to cease. Many of the large objects in our solar system that are not engulfed during that process will be pushed from their orbits during this stage.

This could cause a bit of chaos as planets lose their orbital path and collide into one another or are sent off into the unknown and our solar system will cease to exist. The sun, however, will remain but as it "dies" it will become what is known as a white dwarf. A white dwarf is basically a sun that no longer has thermal fusion occurring at its core and has lost all its radioactive heat causing it to turn white. While a white dwarf has the density of a sun its mass is closer to that of Earth.

As stated before, there are still many questions unanswered within this theory that continues to keep this explanation on the table. However, as this is the best plausible explanation based on what little information we have to date, it is the theory that is most widely excepted. Further studies of planetary systems on the outer edges of our solar system, particularly those in the Oort Cloud and Kuiper Belt, will help us to further understand how our solar system was formed and prove whether or not this hypothesis is correct or not.