Devoted to the recovery, study, and preservation of new meteorite finds.

Home
Falls
Indian Butte
Their Origins
Types of Meteorites
Identification
Finding Meteorites
Ownership
Authentication
Values
Skip Wilson
Metal Detecting
Arizona Falls
About Me

 

The Fall of a Meteorite


 

Speeds and Elevations. In the vacuum of space, meteorites can travel at speeds of 10 to 70 kilometers per second. However, the situation changes rapidly when a incoming meteorite reaches the Earth's atmosphere as air friction exerts tremendous forces on the meteorite.  The transition from vacuum to atmosphere is analogous to doing a belly flop in a swimming pool!

The survivability of an incoming meteorite depends on the physical strength of the meteorite, the speed at which it enters Earth's atmosphere, and on the angle of entry. The chances of meteorite survival increase as entry speed and entry angle decrease thereby minimizing the destructive effects of atmospheric drag.

At 50-100 km of altitude, atmospheric drag brings the meteorite and surrounding air to luminosity. The resulting "fireball" can be brighter than the moon and momentarily turn night into day.  This frictional heating initiates melting of the meteorite's outer surface.  In contrast the interior of the meteorite remains cold because meteorites have low thermal conductivities.

The thickness of Earth's atmosphere increases toward the ground, and at 5-30 km the higher drag causes meteorites to decelerate to 3 - 8 km/s.  At these speeds, the meteoric light extinguishes and the falling meteorite enters into a phase known as "dark flight". The meteorite continues to decelerate and ultimately assumes the behavior of a free-falling object. At this point, the meteorite has lost much of its forward speed and falls nearly vertically to the ground at speeds of 125-250 m/s.

Sounds. The visual phenomena of a bright fireball is often followed by sonic booms, similar the arrival of thunder after a lightening strike. The booms are the result of shock waves that build up in front of the fast-moving meteorite. Observers near the impact site often report a whistle or buzzing sound produced during the free-falling meteorite's final descent.

THE FIREBALL AT DRAKE CREEK, TENNESSEE (MAY 9, 1827)

"On Wednesday the 9th about 4 o'clock P.M. the day being clear as usual, my son and servants were planting corn in the field, they heard a report similar to that of a cannon, which was continued in the air resembling the firing of cannon or muskets by platoons, and the beating of drums as in a battle. Some small clouds with a trail of black smoke, made a terrific appearance, and from them, without doubt, came a number of stones with a loud whizzing noise, which struck the earth with a sound like that of a ponderous body.

One of these stones my son heard fall about fifty yards from where he was. In its decent to the ground it struck a paupau tree of the size of a small hand spike, and tore it to pieces as lightening would have done. Guided by the tree, he immediately found the spot, and there he found the stone about eight or ten inches under the ground; this stone weighted five pounds and a quarter. The stone was cold but had the scent of sulphur. These stones are glazed in a think black crust and bear marks of having been through a body of fire and black smoke".

Fragmentation. Meteorites often break into smaller fragments during atmospheric flight. After fragmentation, the smallest meteorite pieces are rapidly slowed by wind resistance and quickly lose their forward speed. In contrast, the inertia of larger pieces propels them father downstream. The fragments ultimately hit ground in an elliptical pattern known as a strewnfield. This natural sorting of stones has been documented with numerous meteorite falls.

Landing Spots: Perceptions vs. Reality. Meteorite falls are spectacular events, but they can also be deceiving. It impossible for a single observer to accurately determine the size, distance, angle of trajectory, and impact location of a fireball. It is not unusual for people to insist that the fireball was a "big as a car", or landed "just over the hill". After a major fireball, reports from different observers often conflict with one another.

Most likely, a fireball that seemed to strike ground "just over the hill" has disappeared from an observer's view by passing over the horizon. The resulting meteorites, if any survived, may be hundreds of miles away.

On the other hand, sometimes fireballs seem to "burn up" or "extinguish" directly overhead. In reality, the meteor may have entered into the "dark flight" stage of its decent.  There is a chance that meteorites may have landed nearby!

 

www.MeteoritesWanted.com