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No. 44: Mar-Apr 1986

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Atmospheric Footprints Of Icy Meteors

Serendipity triumphs again. From a dayglow experiment aboard NASA's satellite DE-1 (Dynamic Explorer-1) comes an unexpected discovery of considerable potential importance. Looking down on the earth, the DE-1 records the light emitted by atmospheric oxygen at altitudes of about 200-300 kilometers -- this is the so-called "dayglow." The experimenters, L. Frank, J. Sigwarth, and J. Craven, all at the University of Iowa in Iowa City, have found that their dayglow images are speckled with transitory dark spots.

"According to Sigwarth, each hole expands like a drop of dye spreading out in a glass of water; within about 30 seconds the dayglow intensity drops by about 95 percent over an area of about 3,000 square kilometers. Then, over the next 3.5 minutes, the dayglow intensity increases toward its normal value as the hole grows to an area of about 25,000 km2 ."

The Iowa group thinks that the holes or spots are created by meteors hitting the upper atmosphere because the spots follow the same time distribution as meteors. For example, they are more frequent during the well-known meteor showers. The theory is that the dark spots are formed when ice associated with the meteors is turned into water vapor, which reacts with the atmospheric oxygen producing the dayglow, in effect removing temporarily part of the light source. So far, everything seems relatively nonanomalous. But when quantities are calculated, though, jaws begin to drop. The sizes of the spots imply that the average meteor involved weighs 10 kilograms, mostly ice and far larger than has been thought. In fact, they may be characterized as small icy comets; that is, compositionally like the dirty snowballs that comets are now thought to be, but much, much smaller. The implication is that from 1,000 to 10,000 times more material is being added to the earth's atmosphere than previously believed -- most of it being water.

(Weisburd, S.; "Atmospheric Footprints of Icy Meteors," Science News, 128:391, 1985.)

Comment. From this launchpad, one's thoughts can really take off. How much water can this bombardment of icy meteors add to the earth, Mars, and other solar system bodies? In the item under GEOLOGY about the Greenland ice cores, it was indicated that the extraterrestrial dust influx during the Ice Ages might have been as high as 3 x 107 tons per year. If 10,000 times this amount of water is added to the atmosphere from icy meteors, we are approaching 1012 tons of extraterrestrial water per year -- far from an inconsiderable amount. The effects on the earth's climate could be large. If even greater fluxes of icy meteors were intercepted in the past, one might account for "pluvial episodes" on the planets. And further, comets now seem to transport "primordial organic sludge" around the solar system, as mentioned earlier under ASTRONOMY. We will leave further speculation to the reader.

From Science Frontiers #44, MAR-APR 1986. � 1986-2000 William R. Corliss