Ultra-low-frequency microphone

From Correspondent Rick Lockridge

LOS ALAMOS, New Mexico (CNN) -- Current movies like "Deep Impact" and "Armageddon" would have you believe Earth has become a magnet for Texas-sized asteroids and comets hurtling through space.

Actually, most of the rocks and iceballs that pepper the planet burn up high in the atmosphere. Only a few last long enough to give people on the ground a few oohs and ahhs.

Such fireballs are easy enough to spot at night but often pass unseen during the light of day. Unseen, perhaps, but not unheard.

While you can't always see the asteroids and meteors headed our way, scientists at the Los Alamos National Laboratory can hear them with the help of a strange-looking microphone.

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The apparatus, sprawled on the ground of a New Mexico forest, looks like an octopus with hoses for tentacles. Attached to the arms are sensors capable of detecting extremely low pressure, says Los Alamos scientist Douglas ReVelle.  ( 85 K/5 sec. AIFF or WAV sound)

ReVelle uses the ultra-low-frequency microphone to pick up sound waves made by space debris as it slams into the Earth's upper atmosphere at hypersonic speed. ( 145 K/11 sec. AIFF or WAV sound)

Speeded up for the human ear, those sonic booms sound like this: ( 34 K/2 sec. AIFF or WAV sound)

The Earth is constantly invaded by space rocks but most burn up in the atmosphere

Most meteors are tiny but, says ReVelle, some explode high above us with the force of the nuclear bombs dropped on Japan. ( 68 K/4 sec. AIFF or WAV sound)

In such cases the passing fireball can be heard by the human ear alone. The frequency of the sound is so intense it spikes the measuring meter attached to ReVelle's ultra-low-frequency microphone.

While it may sound scary, only Hollywood is preoccupied with the prospect of killer rocks from outer space. Scientists say a truly Armageddon-like impact only happens about once every million years.

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