Chapter 11Meteors, Meteoroids, MeteoritesTypes of MeteoritesAsteroidsSize, Shape, CompositionOriginKirkwood GapsCeresStar Wars vs Real LifePluto (images from NASA)PlutoidsCometsComet TailsComposition of CometsOrigin of CometsShort Period Comets and Meteor ShowersMassive ImpactsMass ExtinctionsTitleChapter 11Other stuff that orbits the Sun(Meteors, Asteroids, Comets, Pluto, etc)Meteors, Meteoroids, Meteorites•Meteors: “Shooting star,” just the streak of light•Meteoroids: The solid body before it enters the atmosphere•Meteorites: The pieces that actually make it to the Earth’s surfaceTypes of Meteorites•Stony, Iron, Stony-Iron.•Most are pieces of asteroids or comets.•Stony: Lots of “chondrules” stuck together, can be ordinary or carbonaceous.•Stony: 4.6 billion years old. Some of first material in solar nebula.•Iron: etching patterns•Stony-Iron: RarestAsteroids•Generally rocky and small.•Most in asteroid belt (2-4 AU)•“Trojan asteroids”•Total mass of asteroid belt is small, but this isn’t why it failed to become a planet.Size, Shape, Composition•Hard to measure•Irregular shape for most (other than Ceres)•Some have moons•Loose collection of rubble held together by gravity.•Carbonaceous, Silicate, or Metallic Iron/Nickel bodies•Different types in different areas of asteroid belt.Origin•How did we get separate rock / metal asteroids?Kirkwood Gaps•TextCeres•Dwarf planet•Contains 25% of asteroid belt’s mass in one object•NASA’s Dawn probe entered into orbit in March 2015•Bright spots: Ice or salts that are reflectiveStar Wars vs Real Life•Average spacing of >1km diameter asteroids is several million km.•Still 100,000s of km between most asteroids•NASA takes considerable effort to make a close fly-by of a single asteroid.Pluto (images from NASA)•Trans-Neptunian Object (TNO)•Discovered in 1930, was a planet for 75 years.•Mass is more than 20x less than Mercury•Pluto and its moon Charon are tidally locked.•Surface is ice, frozen nitrogen / methane, carbon monoxide•Incredibly varied terrain, has an atmospherePlutoids•Several hundred objects orbiting at approximately the same distance as Pluto•3:2 resonance with Neptune —> PlutinosComets•3 main parts: Tail, Coma, Nucleus•Tail: as long as 1AU•Nucleus: block of ice and frozen gas “dirty snowball”Comet Tails•2 tails: Dust tail, Ion tail•Solar wind (ions/cosmic rays) cause ion tail•Radiation pressure (photons) cause dust tail•Tails always point away from sunComposition of Comets•Dust particles fluoresce. Spectra shows water, CO2 CO, trace other gasses•Stardust and EPOXI give closer looks•Deep Impact mission probes underneath surfaceOrigin of Comets•Most from Oort Cloud•These take millions of years to orbit (wouldn’t have much warning if one were going to hit)•Sent into inner Solar System by perturbations, maybe from passing starsShort Period Comets and Meteor Showers•Take less than 200 years to orbit•Come from Kuiper Belt (objects too far apart to form a planet)•Progressively whittled away to nothing by vaporization when near Sun.•Leaves a path of dust along its orbit.Massive Impacts•Most things burn up before they reach the surface•Those that don’t…•Crater in Arizona•Tunguska Event in Russia in 1908•1994 over South PacificMass Extinctions•65 million years ago: Asteroid/comet struck Earth, causing a mass die-off of plant and animal species (most notably, the dinosaurs). •We know this based on the element Iridium.•Mammals are thankful for this.Title•Image Credit: Zach Weinersmith, author of
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