The Solar System: Basics

The Solar System


  • Eccentricity of Orbit: measures the ellipticity of orbit (ranges 0-1, with 0 as spherical and 1 as very elliptical)
  • Density: mass per unit volume; mass in grams and volume in cubic centimeters
  • Oblateness: measures how much the middle section of the planet bulges
  • Surface Gravity: the larger the surface gravity, the thicker the atmosphere as gravity pulls in more gases
  • Albedo: measures the fraction of light reflected compared to the amount of light received from the Sun; the higher the albedo, the more reflective the surface
  • Escape Velocity: minimum speed or velocity needed to escape the planet’s gravitational pull
  • Rotation: most planets rotate in counter-clockwise direction (prograde); others rotate in the clockwise direction (retrograde)
    • Rotational period is shortest for gaseous planets and longest for Venus
  • Roche Limit: about two and a half times the radius of the planet; within the Roche Limit, matter cannot accretes to form moons because the tidal force of the planet tears matter apart to form rings

Giant Planets: Giant planets have lighter elements such as hydrogen and helium in their atmospheres. They have stronger gravity and are at larger distances from the Sun. Jupiter, Saturn, and Neptune are stormy with great spots of lasting storms and belts and zones. However, Uranus is comparatively bland and uniform. All giant planets are home to convection, or hot gases rising and cold gases falling.

Terrestrial Planets: Terrestrial planets have heavier elements such as carbon, oxygen, and nitrogen. Mercury is most heavily cratered while Earth is least cratered. Larger terrestrial planets have plate tectonics. Earth has a sizable magnetic fields that can protect it from solar wind particles and Van Allen Belts. Earth has the “Goldilocks phenomenon,” or the right conditions for the development of life.



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