Monday, January 29, 2007

Meteorite Madness 1


This post will begin a series of posts on meteorites. These posts will be more technical and less subjective than my others, and I hope that the jargon will not dilute the underlying message. I will attempt to make my writing as accessible as possible for everyone from veteran astrogeologists to a Boy Scout with his first telescope. Please join me and my meteorite (right)!

Meteorite Basics

All of our extraterrestrial samples, except for the Moon rocks returned by the Apollo Project, are meteorites. History has documented accounts of stones falling from the sky in every language from Chinese to Greek. Of course, these ancient peoples accounted for the phenomenon in a variety of ludicrous ways. Strong winds would supposedly blow the stones into the sky and from whence they fell back to the Earth. One of the most holy Muslim relics is the black stone (the Hadschar al Aswad) of the Kaaba (left), which is widely believed to be a fragment of a meteorite and may be the oldest preserved fragment from an observed fall. Such was the fate of a meteorite when it fall onto the ancient Earth.

But even after meteorites were recognized as genuine natural phenomena, debates raged over the places and processes of their origin. In 1879, it was seriously proposed that meteorites were terrestrial fragments that had been placed in near-Earth space by immense volcanic explosions. Since then, our understanding of meteorites has progressed slowly and is still in a rather primitive state compared with our current understanding of terrestrial rocks and even lunar samples. This is why we urgently need to divert energy and resources to the problem of meteorites. Although a vast descriptive and analytical literature of meteorites exists, the critical lack of certainty as to their places of origin has severely limited interpretations of modes of meteorite origin and possible genetic relations between different meteorite types.

More than 3600 different meteorites are preserved in collections throughout the world and that number is growing astronomically (pun intended). A meteorite fall may consist of thousands of of stone fragments or individual pieces of iron, but all of these pieces are considered part of the same meteorite. In virtually all cases, multiple falls are known to be the result of a larger individual piece into many more fragments under the immense aerodynamic pressure from the hypervelocity entry of the meteoroid into the dense portion of the Earth's atmosphere. Reported falls of meteorites are common.

If a recovered meteorite was not observed during its luminous passage through the atmosphere as a meteor or bolide, but is recognized as such by its texture, mineralogy, chemistry, surface features or unusual occurrence, it is termed a "find" (as opposed to a "fall"). By international convention, meteorites are named for the closest post office or community to the location of the fall or find that is easily located on a small scale map of the area.

3 comments:

Anonymous said...

Billy,
Your work here is very interesting, and I hope you keep up the good work, but hasn't NASA got any Mars rock? I know we've sent Rovers there.

Anonymous said...

i think the nasa has some lunar rocks but mars is very far away. if you are interested in 'rocking out' on mars, here is a cool internet link!
http://news.bbc.co.uk/2/hi/science/nature/2354533.stm

Billy Susbuck said...

Marvin,
NASA has landed on Mars with their Rovers, but never gotten back off the planet. So we've got electronic data, but no rock hard evidence (!).

Dorothy,
Thanks for the GREAT internet link!