Section 3.4: Orbits in the Solar System

Orbits of Planets

• Closer the planet the shorter its orbital period and higher the orbital speed

• All planets have relatively low eccentricities 

  • An E of 1 or higher is parabolic or hyperbolic → no longer an ellipse 

  • Mercury: Greatest eccentricity of 0.21

• Planetary orbit is confined close to a common plane of the ecliptic - approx 10^o

Orbits of Asteroids

• Asteroids: Orbits with smaller semimajor axes than comets

  • Asteroid belt: Lies between 2.2 and 3.3 AU → Between the orbits of Mars and Jupiter

Comets orbits

• Comets: Larger orbits 

  • Greater eccentricity than asteroids → 0.8 or higher 

  • Move very slowly far away, then speed up close to the sun at perihelion and whips around 

n

n