The Connection Between Asteroids and Meteorites
Chair: Nancy K. Cox, SFAA
Have you ever thought it impossible to touch a piece of an asteroid, or the early solar system, and hold one in your hand? Well, you have – if you have ever held a meteorite – especially an iron meteorite or a stony-iron one!
After much painstaking research, and first overcoming the “impossible” notion that “stones could fall from the sky”, the impossible dream is really true: bits and pieces of the leftovers from the beginnings of the formation of our solar system are delivered to our planet Earth from interplanetary space for our inspection and scientific examination, and they are called “meteorites”. The fact that these bits of metal and rock have such a connection is suggested in the aptly titled book Meteorites and Their Parent Bodies.
This NCHALADA session will review the major classification of meteorite types, and their connection (relation to asteroids), by recent research, including:
Chondrites (stony meteorites): Leftover debris from the formation of the solar system – material that is relatively unprocessed (i.e. was never melted), and are essentially “frozen” (rock) pieces of the original solar nebula!
Iron Meteorites: Due to the process called “differentiation”, wherein over time, the denser materials of a planetary or mooneary body sink to its center and the lighter material rises to the top (the surface). The iron meteorites are pieces of the cores of asteroids (i.e. the iron core, such as resides at the center of our Earth).
Stony-Iron Meteorites: Includes the beautiful pallasites. Green olivine crystals in a nickel-iron metal matrix. When you old one of these meteorites in your hand, you are holding a piece of a core/mantle boundary of an asteroid (iron mixing with the lighter olivine before complete differentiation).
Achondrites: When you see one of these meteorites, you are literally seeing “a chip off an old asteroid”. One example is the Millbillillie meteorite which fell in Australia. It’s a piece of the asteroid 4 Vesta. Studies have shown that the spectra match! HST images of asteroid 4 Vesta have even detected a huge impact crater on it, which probably produced these meteorites, and others called howardites, eucrites, and diogenites. Asteroid 4 Vesta is the third-largest asteroid, 530 km diameter, and the first asteroid to be linked to specific kinds of meteorites.
All of these pieces (in each category) are produced (and some of them reach the Earth), due to the many collisions between the asteroids and these fragments. I will bring samples from my collection of these various types of meteorites.
Far from asteroids being the “vermin of the skies”, the studies of asteroids, and the meteorites which come from them, are a rich source of information and clues to the formation of our solar system — the original materials, and the conditions of the early solar system, further probing an aspect of the never-ending question “where do we come from?”. We cannot touch the stars, but bits of the stars come to us, in the form of meteorites!
Just a few handy references:
Harry McSween: Meteorites and their Parent Bodies. 2nd edition, 2000. Cambridge University Press. The only main reference on this topic, on the relation between asteroids and meteorites, and the research on that.
R. Dodd: Thunderstones and Shooting Stars: The Meaning of Meteorites. Harvard U Press 1986.
F Heide & F Woltzka: Meteorites: Messengers from Space. Springer-Verlag 1995. These 2 have good descriptions of meteorite types.
O. Richard Norton: Rocks from Space. Mountain Press 1994. Richly illustrated, on meteorite types.
John Wasson: Meteorites: Their Record of Early Solar-System History. Freeman 1985. Focusing on interpretations of the origins of meteorites.
J. Burke: Cosmic Debris: Meteorites in History. 1986. History of Meteoritics.
Jay Melosh: Impact Cratering: A Geologic Process. Oxford U Press 1989.
Clark Chapman & David Morrison: Cosmic Catastrophes. Plenum 1989. impacts and geology
John Kerridge & Mildred Matthews, eds: Meteorites and the Early Solar System. U of Arizona Press, 1988.
3 related conference proceedings: Tom Gehrels, ed: Asteroids. U of Arizona Press 1979
Rick Binzel, Tom Gehrels, and Mildred Matthews, eds: Asteroids II. U of Arizona Press 1989
Asteroids III, U of Arizona Press, 2 or 3 years ago.
J. Kelly Beatty, Andrew Chaikin, eds: The New Solar System, 3d ed. Sky Publishing 1990. Pertinent chapters on comets and asteroids.
J. Papike, ed: Planetary Materials. Reviews in Mineralogy, vol. 36. Mineralogical Society of America 1998. Large volume. Scientific discussion of meteorite types, including nonchondritic meteorites from asteroidal bodies as well as from the Moon and Mars.