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(meteorobs) Caltech Question of the Week
Ron Baalke posted the following message about Fireballs on the meteorite
mailing list...just thought you folks would appreciate reading it too.
George Zay
==========
>News Release
>Caltech Media Relations
>Pasadena, CA 91125
>818/395-3227
>
>Caltech Question of the Week
> January 16, 1997
>
>Question: How often do meteors and meteorites fall to Earth?
>Submitted by Bob and Pat Gaskill, Orange County.
>Answered by Dr. William Bottke, Texaco Prize Fellow, Division of Geological
>and Planetary Sciences, Caltech
>
>Meteors and meteorites are small rocky fragments of other planetary bodies
>that fall to Earth. When they do so, they often produce spectacular audible
>and visual effects that can be seen from the ground. Meteorites, objects
>that survive their fiery passage through Earth's atmosphere, are of
>particular interest to scientists, since they are pieces of planetary
>bodies (mostly asteroids) for which samples have not yet been obtained
>through either manned or unmanned space missions. The oldest meteorites are
>remnants of the very first processes to occur in our solar system 4.6
>billion years ago, giving us a glimpse into what conditions were when Earth
>was formed.
>
>One common class of meteor is called a "fireball," named for the bright,
>streaming orbs produced when the surface of a fist-sized or larger body is
>boiled away by friction as it enters Earth's atmosphere. Fireballs
>decelerate from speeds of about 60,000 m.p.h. to 200 m.p.h. during this
>passage, often slowing enough at the end so that they literally drop to the
>ground. Their flight path is similar to a golf ball thrown at an angle
>into a swimming pool; once the water stops the forward momentum of the
>ball, it sinks to the bottom of the pool. The meteor is often not strong
>enough to survive this passage intact, which can make recovery of the
>fragments difficult.
>
>Fireballs are mostly seen crossing the sky at night, though some are so
>bright they can be seen during the day. When a fireball is seen, it is
>usually several miles high. If any surviving meteoritic pieces were to
>survive to reach the ground, they would probably be over 500 miles from the
>observer. If enough people see the fireball from separate locations,
>however, scientists may be able to calculate where the fragments should
>strike Earth.
>
>Studies indicate that about 25 meteorites weighing more than a fifth of a
>pound fall on California (or an area of equal size) each year. Three or
>four of these samples weigh about two pounds and are the size of your fist.
> Using these values, we can estimate that between 300 and 400 of these
>larger meteorites have fallen on California since the turn of the century.
>Most of these rocks, though, have not been found, leaving open the
>possibility that you yourself may discover one someday.
>
>