richardben --
Let's start with three definitions, all from the American Heritage
Dictionary of the English Language, Fourth Edition (2000):
A "meteoroid" is "a solid body, moving in space, that is smaller than
an asteroid and at least as large as a speck of dust."
A "meteor" is a "bright trail or streak that appears in the sky when a
meteoroid is heated to incandescence by friction with the earth's
atmosphere." (Sometimes the term is used interchangeably with
"meteoroid" to refer to the space object itself.)
A "meteorite" is "a stony or metallic mass of matter that has fallen
to the earth's surface from outer space."
So when a rock in space (a "meteoroid") hits the earth's atmosphere it
will create a glowing streak (a "meteor") as it heats up. Any part of
that rock that survives the journey through the atmosphere and reaches
the earth is called a "meteorite."
The trip through the earth's atmosphere results in the burning up of
most meteoroids. There are two versions of the exact nature of the
interaction with the atmosphere that causes the combustion of these
space objects.
The classical version holds that the primary force at work is friction
with the atmosphere (producing heat like that you feel when you rub
your hands together). The newer version, which is now widely accepted
alone or in combination with the "friction" theory, is that the
primary force at work is the compression of the atmosphere directly in
front of the meteoroid.
The simpler "friction" version is offered in this explanation at a
NASA website designed for younger children:
NASA: Kids: Meteors
http://kids.msfc.nasa.gov/SolarSystem/Meteors/Meteors.asp
A plain-English version of the more sophisticated "compression"
version is found here:
"A meteor moving through the vacuum of space typically travels at
speeds reaching tens of thousands of miles per hour. When the meteor
hits the atmosphere, the air in front of it compresses incredibly
quickly. When a gas is compressed, its temperature rises. This causes
the meteor to heat up so much that it glows. The air burns the meteor
until there is nothing left. Re-entry temperatures can reach as high
as 3,000 degrees F (1,650 degrees C)! "
How Stuff Works: Question of the Day
http://www.howstuffworks.com/question308.htm
Space.com, which is a wonderful resource for all topics related to
astronomy, as well as space exploration, explains the "compression"
theory this way:
"When they plow through the atmosphere, meteors are heated to more
than 3000 degrees Fahrenheit, and they glow. Meteors are not heated by
friction, as is commonly thought. A phenomenon called ram pressure is
at work. A meteor compresses air in front of it. The air heats up, in
turn heating the meteor."
Science/Astronomy: Meteors and Meteor Showers
http://www.space.com/scienceastronomy/solarsystem/meteors-ez.ht
Space.com also adds the following interesting details about the origin
of, and the combustion of, meteor[oid]s:
"The intense heat vaporizes most meteors, creating what we call
shooting stars. (Most become visible at around 60 miles up.) Some
large meteors splatter, causing a brighter flash called a fireball,
and an explosion, which can often be heard up to 30 miles away. When
meteors hit the ground, they're called meteorites. Some meteors are
bits broken off asteroids, others -- mere cosmic dust -- are cast off
by comets."
ml
Finally. here is a link to another discussion of the "compression"
theory of the heating of meteoroids. This account states: "The
details of this [compression] process are now fairly well understood
as a result of reentry tests with ballistic-missile nose cones."
Infoplease: Meteors and Meteorites
http://www.infoplease.com/ipa/A0004503.html
Additional Site:
Your further research might be aided by reviewing the websites that
are accessible using the following Google Directories listing:
Google Web Directory: "Asteroids, Comets and Meteors"
http://directory.google.com/Top/Science/Astronomy/Solar_System/Asteroids,_Comets_and_Meteors/
Google Search Terms:
meteors OR meteoroids burn atmosphere
meteors OR meteoroids compression friction
This is a fascinating subject. If any of the information is unclear
or if any of the links don't function, please ask for clarification
before rating the answer.
markj-ga |
