Meteor Research

Every year thousands of meteorites fall to the earth. Only a very small fraction are ever recovered, and even fewer immediately after they fall. Yet there is great value in recovering meteorites quickly, since they contain volatile chemicals that can tell us much about early conditions in the Solar System.

Meteoroids large enough to produce material that can survive to the ground produce brilliant displays called fireballs, which are seen in either the day or the night. Although these light shows may be seen by many hundreds of people, it remains difficult to determine where meteorites might have fallen. Scientists at the Denver Museum of Nature and Science over the last 75 years have perfected techniques for interviewing witnesses and determining the approximate path of fireballs. In this way, several meteorites have been recovered, but most remain lost. For example, what may have been the brightest fireball ever seen over Colorado lit up the sky at 10:44 PM on 17 August, 2001. This event was seen by hundreds of people. Many were visited by Museum researchers, their statements recorded, locations measured, and bearings taken. This produced a map of the likely fall area that narrows things down fairly well:

Meteor Map

Unfortunately, the area identified here is still over 200 square km, in rugged mountains. Although we believe that more than 10 kg of material reached the ground, it is unlikely that it will ever be found.

What is needed is a way of determining the path in the sky of the meteor that is not dependent on the memories of witnesses. The method I am using involves the use of an allsky camera, a camera with very wide angle optics that allows it to see the entire sky down to the horizons. A single such camera can only provide limited information about a fireball, but with a network of cameras, it is possible to view the meteor from different angles, and from that to accurately calculate its trajectory. Through the support of the Denver Museum of Nature and Science, a network of allsky cameras is operating in schools around the state. We hope to be able to pin the impact point of the next big fireball down to just a few square km, and make a speedy recovery. If you are interested in building your own allsky camera, I have some information here.

Leonids

In addition to helping locate fresh meteorite falls, an allsky camera can provide valuable information about the kind of meteors you can see on any clear night, and about annual meteor showers. I was operating two cameras in the Guffey area during the 2001 Leonid meteor storm. This image is a composite of a number of Leonids, including one huge fireball.

Leonid FrequencyThe two cameras between them recorded over 650 meteors. This data has been analyzed to produce a histogram that accurately shows how the meteor rate varied with time, and precisely when the peak occurred.

See my Meteor Shower page for more information about showers and for images from past showers.


Another area of research I am focusing on involves the location of meteors based on the time that low frequency sound waves are received at special listening stations intended primarily for nuclear test ban monitoring. By carefully modeling the propagation of these sounds through the atmosphere and comparing the arrival times at many stations, it is possible to very accurately determine where the meteor first began producing significant acoustic energy.

Atmospheric Model


In addition to operating an allsky camera and analyzing the data from the cameras currently in the network, I am preparing to examine an odd property of bright meteors called electrophonic noise. When meteors are seen, they are usually more than 10 km away. It takes sound some time to travel that far, and witnesses sometimes report hearing sonic booms several minutes after seeing the light. Rarely, however, a sound is heard coincident with the visible meteor. This is not a well understood phenomenon (indeed, some scientists do not believe it is real, or that it represents a psychological effect.) Personally, I believe that it has been reported by enough reputable witnesses to strongly suggest that the sound is real. It is presumably transmitted by some kind of electromagnetic energy, and converted to sound near the witness. One candidate for this is very low frequency (VLF) EM radiation generated in the ionized air produced by the meteor. This VLF energy, in the same frequency range as our hearing, may be transduced to acoustic vibrations by metal objects such as barbecue grills or garage doors. If this theory is correct, it should be possible to record the VLF energy. I am building a receiver for this band that will operate in tandem with my allsky camera. I will be looking for correlations between optically bright meteors and the VLF signals I record. Stay tuned.

If you would like to learn more about meteorites, including how tell if that odd rock you found might be one, visit my meteorite page. If you would like to learn what to do if you see a fireball, or to report one you've seen, click on over to my fireball page.


© Copyright 2007, Chris L Peterson. All rights reserved.