Meteors, Meteorites, and Meteoroids

Meteors

Meteors, Meteorites, and Meteoroids

Meteoroids are debris in space from comets or asteroids; meteors are shooting stars or fire balls in air; meteorites are meteoroids that invade Earth’s atmosphere and impact the ground; micrometeorites are perfect shiny spheres microscopic in size and the major cause of small-scale erosion on the moon. The three major types of meteoroids are stony, stony iron, and iron.

  • Several meteors can be seen per hour on any given night; when this number increases dramatically, these events are called “meteor showers” that occur annually or at regular intervals as the Earth passes through the trail of dusty debris left by a comet
  • The Perseids peak around August 12 every year; each Perseid meteor part of the comet Swift-Tuttle that swings around the Sun every 135 years
  • Other meteor showers and their associated comets: Leonids (Tempe-Tuttle), the Aquarids and Orionids (Halley), and the Taurids (Encke)
  • Comet dust in meteor showers burns up in the atmosphere before reaching the ground
  • Most meteorites no bigger than an average Earth rock
  • Large meteorites can cause extensive destruction: Barringer Meteor Crater in Arizona (1,000 meters, 50,000 years old), asteroid impact which created the 300 km Chicxulub crater on Yucatan Peninsula (65 million years ago)
  • Ann Hodges of Sylacauga, Alabama was severely bruised by a 3.6 kilogram stony meteorite that crashed through her roof in November, 1954
  • Meteorites have a “burned” exterior, formed as the meteorite is melted by friction as it passes through the atmosphere
  • Three types of meteorites: “irons,” “stones,” “stony-irons”
  • More than 30,000 meteorites found on Earth, 99.8% came from asteroids
  • Evidence for an asteroid origin includes: orbits calculated from photographic observations of meteorite falls project back to the asteroid belt, spectra of several classes of meteorites match those of some asteroid classes
  • All but rare lunar and Martian meteorites are very old, 4.5-4.6 million years
  • Only one group of meteorites can be traced to a specific asteroid; eucrite, diogenite, and howardite igneous meteorites traced to third largest asteroid Vesta
  • Meteorites and asteroids that fall on Earth are of the original diverse materials from which planets formed; tells the conditions and processes during the formation and earliest history of the solar system
  • Remaining 0.2% of meteorites split equally between meteorites from the Moon and Mars
  • 35 known Martian meteorites blasted off Mars by meteoroid impacts; all igneous rocks crystallized by magma
  • Controversy of whether structures in meteorite ALH84001 might be evidence of fossil Martian bacteria
  • 36 lunar meteorites similar in mineralogy and composition to Apollo Moon rocks, but come from other parts of the Moon

TIMELINE

4.55 billion years ago: Formation age of most meteorites, age of the solar system

65 million years ago: Chicxulub impact leads to the extinction of dinosaurs and 75 percent of animals on Earth

50,000 years ago: Age of Barringer Meteor Crater in Arizona

1478 BC: First recorded observation of meteors

1794 AD: Ernst Friedrick Chladni publishes first book on meteorites

1908 (Tunguska), 1947 (Sikote Alin), 1969 (Allende and Muchison), 1976 (Jilin): Important 20th century meteor falls

1969: Discovery of meteorites in a small area of Antarctica leads to annual expeditions by US and Japanese teams

1982-1983: Meteorites from the Moon and Mars are identified in Antarctic collections

1996: A team of NASA scientists suggests that Martian meteorite ALH 84001 may contain evidence of microfossils from Mars

2005: NASA’s Mars Exploration Rover Opportunity finds an iron meteorite on Mars

References: NASA <www.nasa.gov>

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