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Small comet controversy flares again.

Small comet controversy flares again

Atmospheric scientists report finding further evidence supporting the controversial theory that tens of thousands of small comets bombard the Earth each day. The researchers have detected apparent signs of water vapor from the comets in an extremely dry portion of the atmosphere about 80 kilometers above the Earth.

John J. Olivero and his colleagues at the Pennsylvania State University at University Park monitored the sky with a microwave radiometer that can detect extremely weak emissions from gases high in the atmosphere. Out of more than 500 days of observations, they found 111 "bursts" of water vapor--a quick rise and fall in the amount of water vapor lasting less than 20 minutes. They suggest the water comes from small comets that enter Earth's upper atmosphere and vaporize due to air friction.

The observations bring new heat to the debate over the existence of such comets. Four years ago, physicist Louis A. Frank of the University of Iowa in Iowa City and his colleagues proposed the theory to explain spots they saw on images of the upper atmosphere taken by satillites looking down on Earth. Frank postulated that 20 of these house-sized fluffy snowballs hit the atmosphere each minute. The theory incited much criticism because if true, it would force Earth and space scientists to revamp many of their long-held notions. For one, it challenges the idea that Earth acquired its supply of water early in the planet's history. If Frank's theory is correct, tiny comets would continually add water to the Earth. While the majority of scientists have reported seeing no evidence of the comets in their data, one other research team, using an optical telescope, has spotted fast-moving objects matching the comet's description (SN: 5/28/88, p.340).

Olivero says he was originally skeptical of Frank's theory, and surprised when his team's observations matched many of the predictions made by the small comet hypothesis. Just as the theory suggests, the researchers see bursts about every four days in their small patch of the sky. They calculate each burst represents about [10.sup.29] to [10.sup.34] molecules of water, a range predicted by the comet theory.

Alex Dessler, a space scientist at Rice University in Houston, says he remains skeptical that the signals in the microwave data come from small comets. The radiometer observations do not confirm some important predictions of Frank's theory, Dessler says. In particular, the bursts do not appear to have a strong daily pattern, whereas the comet theory requires that they appear most frequently between midnight and noon because the comets must approach Earth from behind.

Dessler also says that Olivero has yet to rule out the possibility that an artifact in the instrument caused the observed bursts. He suggests that stringent tests on the radiometer could determine if the bursts are real. If so, the next step is to decipher whether they represent water vapor from comets.
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Title Annotation:comets striking the atmosphere
Author:Monastersky, Richard
Publication:Science News
Date:Jun 9, 1990
Previous Article:Two new cometary molecules.
Next Article:Rivers in a greenhouse world.

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