Mutel and co-author John Fix, professor of astronomy and dean of the College of Science at the University of Alabama in Huntsville, presented their findings at the annual meeting of the American Geophysical Union (AGU) in San Francisco.

In their paper, they described their examination of more than 2,700 photographic images taken with the Iowa Robotic Observatory (IRO), located south of Tucson, Ariz., between Sept. 24, 1998 and June 11, 1999.

"We failed to find evidence that small comets exist," Mutel said. "At the same time, no such search can entirely disprove their existence. But if the small comets do exist, they are present in far smaller numbers than previously predicted."

The small comet theory, developed by fellow UI professor Louis Frank and UI research scientist John Sigwarth, holds that about 20 snow comets weighing 20 to 40 tons each disintegrate in the Earth's atmosphere every minute.

Frank, an internationally known experimental space physicist, defended the small comet theory in a paper published in the Jan. 1, 1999 issue of the AGU Journal of Geophysical Research-Space Physics. The paper described how a mathematical formula was used to filter out instrument noise, or static, from data gathered by NASA's Polar satellite.

The results showed that the dark spots, or atmospheric holes, photographed by cameras aboard the Polar satellite vary in size and number when photographed at different times and at different altitudes. However, some researchers continued to believe that the dark spots appearing in the images are caused by instrument noise.

Mutel and Fix said that their search using the 20-inch IRO reflector telescope was designed so that expected trails would be easily seen without the need for elaborate statistical analysis of faint trails. Observations were made each month within one week of the new moon to maximize sensitivity to faint objects.

The computer-controlled IRO telescope was used to produce multiple shuttered images to distinguish cosmic ray tracks, sensor imperfections and other artifacts from potential small comet trails. The telescope searched for objects moving in the same direction and orbital plane as the Earth at a distance of about 33,000 miles from the Earth.

Out of a total of 6,148 images made, 2,718 were suitable for detection of object trails with magnitude 16.5 (about 10,000 times fainter than the faintest stars visible with the naked eye) or brighter -- easily bright enough to detect the small comets.

The images were recorded on CD ROM, analyzed at the UI, and remain available for independent analysis. Among several UI undergraduates who assisted on the project were Christopher Anson of Muscatine and William Peterson of Iowa City, both seniors. Mutel and Fix said that the search, which was conducted at Frank's suggestion, should have detected more than 80 small comets if they are present in the predicted numbers.

Frank, an experimenter, co-investigator or principal investigator on some 40 spacecraft and an AGU Fellow, first announced the small comet theory in 1986, after examining images recorded in photographs taken by Dynamics Explorer 1.

Frank and his colleagues had designed and built a special camera to take pictures of the northern lights, including the first images of the complete ring of the northern lights from above the North Pole. Some of the images contained unexplained dark spots, or atmospheric holes.

After eliminating the possibility of equipment malfunction and numerous other explanations, Frank and Sigwarth concluded that the atmospheric holes represented clouds of water vapor being released high above Earth's atmosphere by the disintegration of small comets composed mostly of snow.

They calculated that more than 25,000 comets enter the atmosphere each day. At that rate, the comets would have added about one inch of water to the Earth's oceans every 20,000 years -- enough to fill the oceans over billions of years.

Frank said that not only their small size -- 20-to-30-feet in diameter -- makes observation difficult, but also that water striking the upper atmosphere glows very faintly as compared to the bright glow of metal and rock in solid meteors.

The small comet theory was in the news again after the1996 launch of Polar, with its two sensitive visible light cameras and one far-ultraviolet light camera, offered sharper photographic images.

At the May 1997 AGU meeting Frank showed a series of Polar satellite photographs that included a picture of a small comet the size of a two-bedroom house disintegrating thousands of miles above the Atlantic Ocean.

Mutel and Fix said that they were glad to be able to contribute data to the discussion and added that the debate over the small comet theory will likely continue for many years to come.