Meteor Research 2

The following information is basic information on meteors in general.

When a piece of rock from outer space enters Earth's atmosphere, it encounters a lot of friction as it bumps into high-altitude air molecules at very high speed. The friction slows the rock down some, and also heats it up. When the rock passes the temperature of incandescence it begins to glow brightly and can be seen from the ground.

One of four things happens next:

(A) If the meteor approaches from a shallow angle, it can actually "skip" back out of the Earth's atmosphere, similar to what happens to a rock you skip across a puddle. Once it leaves the upper atmosphere and is no longer being heated by friction, it cools below the point of incandescence (visible light by a hot object) and fades out.

(B) Most meteors burn up (meaning they vaporize completely) long before reaching the ground. Their atoms are ripped apart by the intense heat and scattered to the wind. The dust will eventually settle to Earth, but it will be microscopic particles.

(B-1) Rather than simply vaporize, some meteors explode. It's thought that a massive meteor explosion caused the famous Tunguska blast in 1908. This is a relatively rare event, however. Tunguska blast- The Tunguska event was an enormously powerful explosion that occurred near the Podkamennaya Tunguska River in what is now Krasnoyarsk Krai, Russia.

(C) If the meteor is large enough, it can survive its plunge to the ground. At this point it is called a meteorite. Very few meteors survive all the way to the ground, since most of them are so tiny. Incidentally, a meteor that makes it to the ground won't even be that hot upon landing. Once the Earth's atmosphere slows it to its terminal velocity, it will have plenty of time to cool before it reaches the ground.

(D) Any meteor large enough that it doesn't have time to cool before reaching the Earth is going to make a pretty big impact anyway. The meteorite will probably be destroyed in the impact event, and you'll be lucky to find more than a shard. But don't worry...impacts of this magnitude are exceedingly rare. 

When a Meteoroid Becomes a Meteor 

The relative speed of a meteoroid to the Earth at the moment of collision is typically in the range of 25,000 to 160,000 miles per hour (40,000 to 260,000 kilometers per hour), and friction with the air particles in the upper atmosphere immediately begins to burn off the outer layer of the object. Small particles are usually completely consumed, but moderately sized ones may survive to the point where they completely lose their cosmic velocity and begin to fall to the ground under the force of gravity. Scientists call this the retardation point, and it is typically several miles above the ground. 

Meteorite Temperatures

The process by which a meteor glows when moving through the upper atmosphere is called ablation and it stops at the retardation point. If the meteor hasn't been completely consumed, it falls to the ground as a dark rock. Scientists believe that meteorites are probably cool when they hit the ground, because the hot outer layers have all fallen away during ablation. Approximately 10 to 50 such rocks hit the Earth every day, with about two to 12 being potentially discoverable, according to the American Meteor Society. Large ones are named after the place at which they are found. Some notable ones are the Nantan meteorite that fell in China in 1516 and the Launton meteorite that fell in England in 1830.

Potential for Catastrophe 

Meteoroids weighing more than about 10 tons (9,000 kilograms) retain some of their cosmic velocity and hit the ground with more force than smaller ones. For example, a 10-ton meteoroid can retain about 6 percent of its cosmic velocity, so if it's originally moving at a speed of 90,000 miles per hour (40 kilometers a second), it can hit the ground at a speed of 5,400 miles per hour (2.4 kilometers per second), although a considerable portion of it would have burned away. Atmospheric drag would have a negligible effect on a meteoroid with a mass of more than 100,000 tons, or 90 million kilograms.

Sounds of meteors

Sound generated by a meteor in the upper atmosphere, such as a sonic boom, is typically delayed for many seconds after the meteor disappears. Occasionally, as with the Leonid meteor shower of 2001,"crackling", "swishing", or "hissing" sounds have been reported, occurring at the same instant as a meteor flare. Similar sounds have also been reported during intense displays of Earth's auroras.

Sound recordings made under controlled conditions in Mongolia in 1998 support the contention that the sounds are real.

How these sounds could be generated, assuming they are in fact real, remains something of a mystery. It has been hypothesized by some scientists at NASA that the turbulent ionized wake of a meteor interacts with the magnetic field of the Earth, generating pulses of radio waves. As the trail dissipates, megawatts of electromagnetic energy could be released, with a peak in the power spectrum at audio frequencies. Physical vibrations induced by the electromagnetic impulses would then be heard if they are powerful enough to make grasses, plants, eyeglass frames, and other conductive materials vibrate. This proposed mechanism, although proven to be plausible by laboratory work, remains unsupported by corresponding measurements in the field.

The research was provided from the following websites;

http://en.wikipedia.org/wiki/Meteoroid

http://science.opposingviews.com/happens-meteoroid-enters-earths-atmosphere-3611.html

http://answers.yahoo.com/question/index?qid=20071214194042AAccCgB