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How Do Planets Form?
The first step in planetary formation is the collapse of giant interstellar clouds that form stars. Turbulence within these clouds gives rise to regions with sufficient mass that the gas and dust begins to collapse under its own gravitational attraction. As the cloud collapses, the material at the center begins to heat up. A hot core forms and when it heats up sufficiently, it will begin thermonuclear fusion and become a star. As the cloud shrinks, its rotation speeds up to conserve angular momentum (think spinning ice skater pulling her arms in). Once a cloud has collapsed sufficiently, a rotating disk-shaped nebula made of dust and gas, known as an accretion disk, forms. Some of the material ends up as part of the star, and some may become planets, asteroids, moons or comets.
How does the dust and gas become planets?
While the process is still somewhat unknown, many scientists believe it was a combination of two important forces, gravity and electrostatic charge. Scientists think that electrostatic charges in the spinning nebula may have resulted in cohesion forces between very tiny dust grains.
This phenomenon may be responsible for the initial aggregation of dust grains that started the formation of the planets. As dust grains stuck to other grains, the clumps got larger and became attracted to other clumps by gravity. Larger clumps of matter collided with other clumps (and some were crashed apart!) and over time the planets were born, sweeping out large regions of the solar system. Check out this neat video to see: Planet Formation Animation .
Electrostatic accretion and bonding may therefore be a process of basic importance in the solar system. How does this work?
Everything we see is made up of tiny little parts called atoms, that are made of even smaller parts called protons, electrons and neutrons. They are very different from each other in many ways. One way they are different is their "charge." Protons have a positive (+) charge. Electrons have a negative (-) charge. Neutrons have no charge. The protons and neutrons in the nucleus of the atom are held together very tightly. But some of the outer electrons are held very loosely. If you rub things together, electrons can move from one atom to another. Some atoms get extra electrons, these will then have a negative charge. Other atoms lose electrons; these will then have a positive charge. When charges are separated like this, it is called static electricity. If two things have different charges, they attract, or pull towards each other. If two things have the same charge, they repel, or push away from each other.
You can easily create and visualize an electrostatic charge on Earth by rubbing your hair against a balloon and then placing it over a plate of sugar or near small pieces of Styrofoam, which will cling and clump together.
Richard Garriott planned to demonstrate electrostatic charge build up by shaking dry coffee grinds in a plastic bag in space, however due to limited time he was unable to complete the activity. What do you think would have happened?
Essential Questions
- What two important forces helped to form the planets around the Sun?
- What causes static electricity?
Classroom Activities
Elementary
Middle/High School
Challenger Center Formation of the Solar System Lesson
Student Resources
Elementary
Bill Nye video - Static Electricity
Watch this Bill Nye video link below to see the sugar grains jump onto the balloon!
Middle/High School
Planet Formation from Stardate
Videos
Teacher Resources
Static tubes are made of clear plastic and have tiny Styrofoam balls inside that will jump and clump when you rub the tube.
Science articles on electrostatic charges and planet formation (these are college/graduate level)
Charge Transfer in Dust-Agglomerate Collisions and the Efficiency of Electrostatic Secondary Agglomeration
