Comets and Asteroids

• Comets and Asteroids


  Celestial bodies that orbit around the Sun and are small bodies in the solar system
• Comets and Asteroids

  • Time capsules that contain information about the history of the solar system
  • From debris left over from the formation of the moon or other parts of the solar system
  • Occasionally change their orbital path due to gravitational disturbances, sometimes bringing them close to a planet (mostly for comets as asteroids are more stable)
  • Craters on the moon are evidence of the history of impacts of these celestial bodies (mostly from asteroids)
  • Formed 4.6 billion years ago
• Comets

  • Eccentric orbit
  • Made of rocks, hydrocarbons, and ice
  • Has a thin, temporary atmospheric tail when close to the Sun
  • Orbital period: 75 to more than 100,000 years
  • 1 to 10 kilometers in size (nucleus)
• Asteroids

  • Elliptical orbit
  • Made of metals and rocks
  • Does not produce a coma or a tail atmosphere
  • Orbital period: 1 to 100 years
  • 1 to larger than 100 kilometers in size
• Comets

  • Located in the outermost regions of the solar system
  • In the Kuiper Belt (region beyond Jupiter) or the Oort Cloud (sphere of ice objects that surrounds the solar system)
  • Made of dust, ice, and rock materials
  • Formed farther away from the sun where ice remained solid
• Comet approaching the Sun

  1. Part of its ice melts

  2. Other materials vaporize due to the Sun's heat

  3. Resulting in a glowing halo that extends outwards
• Coma

  The ice and compounds (ammonia, methane, etc.) develop a fuzzy cloud-like shell
• Famous comets

  • Halley's Comet
  • Comet Hale-Bopp
  • Comet Hyakutake
  • Comet Shoemaker-Levy 9
• Halley's Comet


  • Has an elliptical orbit and returns to the inner solar system every 75 to 76 years
  • Last time it was close to Earth was in 1986
• Comet Hale-Bopp


  • Visible to the naked eye for a record of 18 months in 1997
  • Had a long, dusty tail and a greenish coma
• Comet Hyakutake


  • Another naked-eye comet in 1996
  • Had a long, double tail, one made of dust and the other of ionized gas
• Comet Shoemaker-Levy 9


  • Broke apart into several pieces before colliding with Jupiter in 1994
• Asteroids

  • Located in a belt between Jupiter and Mars
  • Composed of rocky materials and metals
  • Made up of metals, rocks, and organic compounds
  • Formed much closer to the sun
  • Do not have a coma like a comet
  • Have shorter and elliptical orbits
  • Some measure hundreds of kilometers across while some are as small as dust particles
  • Some have orbits that take them closer to the Sun and a few even cross the Earth's orbital path (NEOs or near-Earth asteroids)
• Asteroids

  • Ceres (largest asteroid that is more like a small planet than a rock)
  • Vesta (second-largest asteroid; brightest asteroid and can sometimes be seen with the naked eye)
  • Pallas (known for its unusually shaped orbit)
  • Bennu (near-Earth asteroid)
  • Ryugu (near-Earth asteroid)