Planets as We Know Them

A planet is only one type of world which might be chosen as a setting for a geofiction. Moons are another popular setting especially in science fiction. There are many other celestial bodies that could be called a world. Planets make great earth like worlds and are the most popular setting for Geofictions.

The Planet in our Solar System

The Planets in our Solar System –  Image Credit: Lunar and Planetary Institute

IAU Definition of a Planet

In 2006 the International Astronomic Union (IAU) changed the definition of a planet. The full resolution was:

RESOLUTION 5A

The IAU therefore resolves that planets and other bodies in our Solar System, except satellites, be defined into three distinct categories in the following way:

(1) A “planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighborhood around its orbit.

(2) A “dwarf planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighborhood around its orbit, and

(d) is not a satellite.

(3) All other objects, except satellites, orbiting the Sun shall be referred to collectively as “Small Solar-System? Bodies”.

The eight recognized planets by the IAU are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

 Links for Learning

9 PlanetsThe NineEight Planets

Link to external websiteLunar and Planetary Institute

Link to external websiteSolar System Exploration

Link to external websitePluto and the solar system

Questions for World Builders

These questions can also be applied any type of world.

  1. What is the general shape of your world?
  2. How did it become this shape?
  3. What is the distance of the world from the nearest Sun?
  4. Does your world have any moons or other satellites?
  5. How old is your world?
  6. How big is your world?
  7. If you dissected your world in half, what would you find beneath its crust?
  8. What are the core compounds and chemicals that are found in your planets atmosphere.
  9. What is the gravity of your planet?
  10. Does your world tilt?
  11. If your planet has poles, where are they located?

Fun Projects

  1. Map the orbit of your world around its solar system.
  2. Draw a segmented diagram of your planet showing the various layers within.
  3. Jot down at least 10 dot points about the creation of your world in scientific terms.
  4. Make the shape of your planet out of paper mache.

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