The new cameras. Images from cameras on other spacecraft which could confirm the existence of atmospheric holes were not available until the launch of the Polar spacecraft on February 24, 1996. The reasons for this were several: the images must be taken in the special ultraviolet window, provide a view of a large section of the daylit atmosphere, and have sufficient resolution to detect an atmospheric hole. The intervening interval of ten years since the report of images from Dynamics Explorer- 1 was a period of relatively quiescent activity during which the scientific community became further convinced that the atmospheric holes in the images were simply due to camera noise. In this quiet atmosphere another set of auroral cameras was being constructed at the University of Iowa for the Polar spacecraft. The capabilities for the detection of atmospheric holes, and of the small comets, were also objectives of these cameras. These cameras were the most sophisticated scientific instruments ever built at the University of Iowa. If atmospheric holes and the small comets existed, the resolutions and capabilities of these cameras would leave no doubt.
|Figure 5. University of Iowa scientist John Sigwarth viewing the cameras on the Polar spacecraft just before launch.|
These new cameras were capable of greatly extending the previous observations with Dynamics Explorer- 1 in three important, independent ways. First of all the atmospheric holes could be observed with much greater spatial resolution, which provides confirmation beyond any reasonable claims of "camera noise." Secondly, the sky in the vicinity of our planet could be monitored for bright trails due to the glow of oxygen from the disruption of some of the comets at very high altitudes of thousands of miles. Thirdly, the new cameras would allow optical detection of the fragments of water molecules as the cometary clouds plummeted into the atmosphere.
The Polar spacecraft and its cameras were successfully launched and the complex process of turning on these sophisticated cameras proceeded during the month of March 1996. John Sigwarth was at the control center at NASA's Goddard Space Flight Center in Greenbelt, Maryland during this critical period. I will always remember a telephone conversation with John during which a lengthy discussion of camera voltages, currents, and temperatures occurred. At the end of this conversation, John quietly said "Oh, yes, by the way, the atmospheric holes are clearly present in the images."
Although John and I knew that the above three confirmations were successful by late Fall of 1996, it was clear to us that we needed some "quiet time" to achieve a careful, thorough analysis. Our silence during this period of over a year after launch was greeted by most scientists with relief that the atmospheric holes and small comets must not exist. When the results were finally reported at a NASA-supported press conference at the American Geophysical Union meeting during May 1997, there was great turmoil and confusion in the scientific community and the announcements raced like a wildfire through the press.
|Figure 6. Detection of an atmospheric hole over Poland with a camera on the Polar spacecraft.|
The confirmation of the existence of atmospheric holes with the Polar cameras is demonstrated by the ultraviolet image shown in Figure 6. This atmospheric hole is positioned above Poland and was recorded on April 6, 1996. It is remarkable that the rate at which these atmospheric holes occur in the atmosphere is very similar to that previously observed with Dynamics Explorer-1, even though the cameras were greatly different.
The second independent confirmation was also provided by the camera for ultraviolet wavelengths. A few of the small comets were disrupted at much higher altitudes than for the vast majority of comets impacting the atmosphere. For those which were bursting at the higher altitudes, trails of bright glows from atomic oxygen were clearly observed. An example of such a trail is shown in Figure 7. This picture was taken on September 26, 1996. The bright trail of the gases from the disrupted comets has been superimposed upon a map of Earth generated by a commercial computer program in order to provide perspective as to the view seen by the Polar camera. The trail moves across the Atlantic Ocean and ends above Eastern Germany. Such photographs never had been taken by any previous spacecraft. Note that the images in both Figures 6 and 7 show atmospheric impacts at locations other than the North American continent. Because of the emotional reactions of a group of scientists in the United States to the amazing set of new images, we had decided that it was best to show impacts in other locations for the first press releases in order to ameliorate the situation. Indeed cometary trails above the Northern Hemisphere are observed. An example of a trail captured in a photograph on September 28, 1996 above San Diego, California is shown in Figure 8. Such pictures provide undeniable evidence that a new class of objects has been discovered in the vicinity of Earth.
|Figure 7. Discovery of the oxygen trail of a small comet as it moves across the North Atlantic toward East Germany.||Figure 8. Another oxygen trail, but over San Diego, California.|
|Figure 9. Two pictures of the large Comet Hale-Bopp, the upper picture for fragments of water molecules and the lower for sodium and dust.|
Finally, as a third independent verification of the existence of the small comets, another of the three cameras was used to search for the cometary water impacts into the atmosphere. These pictures were taken in light that was nearer to the range of our eyesight but still a little too far into the violet to see. However, this was a wavelength which is used frequently to monitor the well-known large comets. This light is emitted as the Sun illuminates the fragments of cometary water vapor, specifically the fragment produced when a hydrogen atom is stripped from a water molecule. In order to calibrate our cameras on the Polar spacecraft we pointed them toward Comet Hale-Bopp as it approached the Sun. This was very exciting and instructive for us. Images in two different colors of light are shown in Figure 9. The top picture shows this large comet as seen in the light from the fragments of water vapor as noted above. The bottom photograph is taken in the light emitted by sodium and also light scattered from cometary dust. The sodium is to be found in the remarkable thin trail at the top and the rest is due to dust. Thus the Polar cameras were shown to be very capable of detecting cometary lights.
|Figure 10. Three snapshots of the water fragments in the water cloud of a small comet impacting our atmosphere.|
But there was a surprise awaiting us when we turned the cameras to view the small comets which were impacting the Earth's upper atmosphere. The light from the water fragments was dramatically seen in the sequences for each comet, one sequence of which is shown in Figure 10. The surprise was the absence of sodium and dust in these water clouds of the disrupted small comets. This provided the explanation for one puzzling aspect of the small comets, the absence of very bright trails during the atmospheric impacts. Sodium and dust provide bright impact glows, but water and its fragments are much dimmer. Thus the composition of the small comets is significantly different than that of the well-known large comets. It was rewarding to compute the amount of water vapor in the small comets from measurements of the brightness of the light emitted by the water fragments. The mass of water in a single comet was about 20 to 40 tons, and confirmed the result obtained independently from observations of atmospheric holes. Complete closure was obtained when the measured frequency of water trails such as that shown in Figure 10 was found to be very similar to the occurrence rate of atmospheric holes such as that displayed in Figure 6.
The opinions of the scientific community greatly changed after the announcement of the Polar results in May 1997. A majority of the scientists offered congratulations on the confirmation of the earlier Dynamics Explorer results. The public was very supportive of these findings which promised to provide new insight into our origins. But a minority of scientists, very vocal and organized, fought against the breach in dogmas offered by the small comet findings. There were presentations of results and opinions which drew more than a thousand spectators at the national meetings of the American Geophysical Union. The atmosphere was extremely combative and the presentations were then based upon emotions rather than sound scientific reasoning. Of course, it was immensely entertaining for those who were merely spectators. A good characterization of these heated encounters was offered by science writer Patrick Huyghe, who has closely collaborated with me on numerous occasions in communicating with the public and the scientific community, in the [Frank Cotham New Yorker] cartoon shown in Figure 11 [Not shown. This cartoon shows two men crouched behind a speaker's table. Bullets are flying over them in the air. While one man fires back with a machine gun, the other says: "This symposium has gotten completely out of hand!"].
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