1. Concepts 2. Solar System Origin 3. Planetary Processes 4. Earth Processes 5. Meteorites
6. Our Moon 7. Remote Sensing 8. Mercury 9. Mars 10. Venus, Our Twin
11. Jupiter & Jovian Moons 12. Saturn, Rings & Moons 13. Uranus 14. Neptune 15. Pluto, Charon & Comets

Origin of the Solar System

Read the introduction, re-read Chapter 2, read Chapter 3 in The New Solar System.

The Big Bang

Our Solar System is one of innumerable systems that comprise billions of galaxies strewn about the universe. One theory of the origin of the universe is that a tremendous release of energy (i.e. an explosion) called the "big bang" initiated the formation of matter approximately 15 billion years ago. This is partly suggested by the astronomical observation that the universe is expanding; the expansion is projected backwards in time to some initial state.


Read this article about the "Big Bang Theory" taken from the Supernova Cosmology Project from the Berkeley Lab.

Visit the project website: (http://www.lbl.gov/supernova/).

Animation by Lawrence Berkeley National Laboratory's Computer Visualization Laboratory (N. Johnston: animation) at the National Energy Research Scientific Computing Center.
Visit some or all of these pages to learn more about the Big Bang Theory:

Humans cannot comprehend such a formidable event, yet we call upon theoretical processes derived from studies of subatomic particles and the interaction of matter and energy. Part of Einstein’s legacy is a more comfortable acceptance of nuclear processes as part of nature and the way our universe works. So, we mere humans try to attach significance to the Big Bang theory, but all it really does is serve as a starting point. It is quite possible that the Big Bang, if applicable, represents one event in a never beginning, never-ending cycle.

Now, with that out of the way, let’s assume that protons, neutrons and other particles were formed in some major event. The simplest and lightest element is hydrogen (H), the most abundant element in the universe. Each atom of hydrogen contains one proton, having an atomic mass of unity, plus 0, 1 or 2 neutrons that add to the atomic mass. Each form of H is thus an isotope of that element having an atomic mass that is the sum of the number of protons and neutrons.

Hydrogen with one neutron is deuterium (D or 2H) and has the same chemical properties as H. When D combines with oxygen, it forms D2O, which is heavy water. Ice formed from pure D2O sinks in normal water. What is tritium?


Physicists believe that the lightest elements (deuterium, helium, and lithium) were produced in the first few minutes of the Big Bang. Others are produced in supernovas.



Although humans do not have any final idea of how the simplest subatomic particles of matter are actually created, we do know that matter and energy are interchangeable. We also know that matter is transformed in stars, thus we consider all matter in the universe to be created in stars or to have gone into the formation of stars. Most scientists studying the big bang generally believe that nuclei of only hydrogen and helium were created in the big bang. These two elements were the dominant components of the earliest stars. Elements heavier than He were synthesized later inside stars by nuclear fusion.

Hydrogen Fusion


The figure illustrates hydrogen fusion to form helium. Hydrogen (H) nuclei, which are just protons, collide to produce heavier nuclei. When protons collide one of them (at least) gives off some energy in the form of a positron (e+), i.e. a particle equivalent to an electron except that it has a positive charge instead of a negative charge. Since protons are positively charged, the emission of a positive charge makes the proton change into a neutron (so a neutron is a proton that has lost its charge and vice-versa). More collisions, at least the ones that stick, cause heavier elements such as D, 3H and He to form. Massive stars are capable of fusing even heavier nuclei such as C, O, Ne, etc.  Click the picture to see a larger digram.

The highest elemental mass that can be created in a star depends on the mass of the star itself. The dominant reaction in stars like our Sun is the fusion of hydrogen into helium, whereas some very massive stars are capable of producing much heavier elements.




Layering in Stars

Fusion depends on confinement pressure so heavier elements are formed deep within a massive star and lighter elements make up the outer layers. This diagram is definitely NOT scaled correctly. To learn this in more depth read this pdf version from the T. H. Huxley School earth materials modules created by Martin Palmer.

Isotopes of the heaviest elements, up to atomic number ninety-two, are produced when a cataclysmic explosion, such as a supernova, destroys a star. This is a fundamental aspect of nucleosynthesis, the formation of elements that could later become involved in construction of a new solar system. Since it is a normal part of the stellar life cycle, we expect that our Sun will someday terminate with an explosion and perhaps yield essential components for another star system.


Fusion depends on confinement pressure so heavier elements are formed deep within a massive star and lighter elements make up the outer layers. This diagram is definitely NOT scaled correctly (see previous page.)

What is a Supernova?

Studies of the Great Supernova on February 23, 1987 allowed the first closeup view of a star explosion since the year 1604. For a detailed discussion see the article "The Great Supernova of 1987" by Stan Woosley and Tom Weaver, in Scientific American, August, 1989. They show that new theories and observations lead to a better understanding of the most likely processes and structure of such a star immediately before its death. The presupernova star was structured like a "cosmic onion" made up of concentric shells of elements with the heavier ones closer to the center:

Structure of the Cosmic Onion (pre-supernova star):

Radius of Shell Composition of Shell
(degrees K)
30 million km
#1 H + He
18 solar masses
500,000 km
#2 He
#3 He + C
20 million
1 g per cm3
6.1 solar masses
50,000 km
#4 C + O
#5 O + Ne + Mg
250 million
1000 g per cm3
3.9 solar masses
5,000 km
#6 Si + S
#7 Fe
3 billion
1 million g per cm3
1.9 solar masses

(after Woosley and Weaver, 1989)

Onion-like Star Structure

onionstar onionstar2



This diagram illustrates the approximate thickness of each compositional layer in the cosmic onion. It is obvious that the greatest bulk in any star is comprised of H with minor He and relatively miniscule amounts of heavier elements! (after Woosley and Weaver, 1989)


The Search For Evidence

Humans will always try to discover more about the origins of the universe, planets, life, etc. The NASA program "Cosmic Origins" offers educational outreach materials and tutorials.




Our Galaxy . . .

. . . The Milky Way, is somewhere around 14 billion years old, but our Solar System is "only" about 4.5 billion years old. Assuming that all of the matter in our system was derived from dying stars or interstellar gas clouds within the galaxy, then several star systems probably preceded our current star and so our solar system, therefore, contains many recycled elements. The relative abundances of elements in our Solar System give clues to its history.

The following table of cosmic abundances lists the major elements in our system relative to every 1 million hydrogen atoms. The list also shows the percentage of each element in the Sun.

You should be somewhat familiar with all of these common elements because part of planetary geology is understanding the composition of planetary interiors…. which are made up of rocks….. which are made up of minerals….. which are made up of atoms……

Solar System (Cosmic) Abundances of the Major Elements

Adapted from Beatty and Chaiken, 1990 (chapter 2 by Robert W. Noyes); and Morrison and Owen, 1987.

Element Symbol Atomic Number Atoms per 106 Hydrogen Atoms Percent in Sun
Hydrogen H 1 1,000,000 92.1
Helium He 2 68,000 7.8
Carbon C 6 420 0.030
Nitrogen N 7 87 0.0084
Oxygen O 8 690 0.061
Neon Ne 10 98 0.0076
Sodium Na 11 2 (trace)*
Magnesium Mg 12 40 0.0024
Aluminum Al 13 3 (trace)*
Silicon Si 14 38 0.0031
Sulfur S 16 19 0.0015
Argon Ar 18 4 (trace)*
Calcium Ca 20 2 (trace)*
Iron Fe 26 34 0.0037
Nickel Ni 28 2 (trace)*
      *All Others 0.0015

Ninety-nine percent of the mass of the Solar System is made up of hydrogen and helium. Obviously, relative to H and He, there doesn’t seem to be much matter left to form rocky and icy planets. What processes would enable the formation of a sun and various types of planetary bodies from a large nebulous cloud of gas and dust? Materials that formed planets and other objects condensed from the solar nebula as it collapsed and cooled.


Imagine a low-density cloud of interstellar dust and gas that became increasingly more dense under gravitational contraction. Eventually the cloud began to collapse and rotate as it contracted to higher and higher density. The rotation rate increased in order to conserve angular momentum and the cloud flattened out into a pancake-like disk.

The disk developed two major components: the central part, or core, and the rapidly spinning cloud of dust and gas surrounding the core. The core eventually became hot and dense enough to sustain thermonuclear reactions as discussed above. Planetary bodies formed in the surrounding disk as small dust particles accreted into larger rocky ones which, in turn, collided and grew into even larger ones.

Compression generated heat so that the nebula developed a temperature gradient like the one shown in the graph. Regions closer to the core were much hotter than regions in the outer part of the disk. Distance from the proto-Sun was a major factor in determining the temperature of the cloud. The significance of the temperature gradient is inherent in the compositions and physical properties of the planets. Terrestrial planets, Mercury to Mars and the Asteroids, formed in the hottest part of the nebula; whereas the large "gaseous" planets, Jupiter to Neptune, formed in the cooler regions.

Within each of these two groups (the inner and outer planets) there exists compositional changes derived from the temperature gradient. For example, water ice could condense at 5 astronomical units (AU)*, but not at 2 AU. Some silicate molecules, the building blocks of rock-forming minerals, could condense at 1 AU, but not at the center of the nebula. Inside approximately 0.2 AU the temperatures were never low enough to allow condensation of solids of any kind (Morrison and Owen, 1987).

*An astronomical unit is the average distance of the Earth from the Sun.


This chart (click to see a larger version) illustrates the sequence of mineral condensation within the approximate temperature regime of a cooling solar nebula gas cloud.

Study the chart and compare it to what you know about planetary compositions. This will become more important later in the term. In this sequence, minerals that formed at high temperatures became restructured and incorporated into different compounds at lower temperatures as they reacted with the cooling gas.

This means that a mineral that existed in the earliest stages of condensation was eliminated later as long as there was sufficient time for reaction. Some high-temperature minerals, like perovskite and melilite, actually were preserved in parts of the nebula that cooled rapidly. These were trapped into bodies that could not have sustained a high temperature and thus were quite small, such as CAI’s (Calcium-Aluminum Inclusions) found in some meteorites.

Words and People to know:     Glossary
Big Bang
atomic particle
white dwarf
cosmic onion, onion star
Black Hole
mass spectroscopy
globular cluster
T-tauri stage
Large Magellanic Cloud
B2FH paper
George Gamow
Georges Lemaitre
Arno Penzias & Robert Wilson
brown dwarf
red giant
Doppler effect
red shift
background radiation
dark matter
periodic table
atomic number
atomic mass
stellar life cycle

Assignments 1, 2 and 3 in .doc format.

The following are some good websites that might be helpful. They are not required reading.  

What other websites can you find to help you understand the UNIVERSE?

References for Further Reading:

Hartmann, William K., Moons and Planets, 3rd edition. Belmont, CA: Wadsworth Publishing Company, 1993.

Morrison, David, and Tobias Owen, The Planetary System, Addison-Wesley Publishing Company, Reading MA, 519 p., 1987 (ISBN 0-201-10487-3, a bit dated, but still an excellent textbook with lots of fundamental concepts.)

Osterbrock, Donald E., editor, Stars and Galaxies -- Citizens of the Universe, Readings from Scientific American Magazine. W.H. Freeman and Company, New York, 184 p., 1994. (ISBN 0-7167-2069-8, a collection of articles dealing with pioneers in astronomy, galaxies, luminous stars, supernovas, and more)

End Of The Module
On to Module 3