Asteroid, comets, Dwarf planets and cosmic collisions

• Asteroids are leftovers of planet formation. They are mostly rocky and are found in the asteroid belt between Mars and Jupiter.
• Asteroids are cratered and not round.
• Trojan asteroids follow Jupiter's orbit.
• Why is there an asteroid belt?

  Orbital resonances with Jupiter prevented planetesimals between Jupiter and Mars from forming a planet
• Meteor: bright trails left by a meteorite.
• Meteorite: a rock from space that falls through Earth's atmosphere.
• comets:

  • form beyond the frost line, comets are icy.
  • The nucleus of a comet is a dirty snowball.
  • Most comets do not have tails (only the ones that enter the inner solar system grow tails)
  • most comets remain frozen in the outer solar system.
• Anatomy of a comet:

  A) coma

  B) nucleus

  C) ion tail

  D) dust tail

  
• coma: it is the atmosphere that comes from a comet's heated nucleus.
• Plasma/ion tail: gas escaping from the coma, pushed by solar wind.
• A dust tail is pushed by photons.
• Where do comets come from?

  Oort Cloud and Kuiper Belt
• Kuiper Belt has comets in plane of solar system. (short period)
• Comets on random orbits come from the Oort cloud. (long period)
• Is pluto a planet?

  No. Much smaller than terrestrial or jovian planets.

  • Has icy composition like a comet.
  • Has a very elliptical, inclined orbit.
  • more in common with comets than the 8 major planets.
• Eris is the same size as Pluto.

  • They are both classified as dwarf planets.
• In the asteroid belt, Ceres is also considered a dwarf planet.
• Giant impact: This stripped matter from Earth's crust. Stripped matter began to orbit and then accelerated into moon.
• giant impacts also explain the odd rotation axes of some planets.
• Origin of Earth's water: icy planetesimals.
• Evidence of an impact on Earth is Iridium; which is very rare in Earth's surface rocks but often found in meteorites.
• Dinosaur fossils lie below the iridium layer.
• Mass extinction occurred 65 million years ago; which killed the dinosaurs.