The final frontier. In a desolate place not far from Tombstone, Arizona is a robot telescope from the University of Iowa which was constructed and is operated under the guidance of Robert Mutel, a professor at our university. The building which houses the telescope is shown in Figure 26 [below, left]. The roof of this building rolls to the left to allow the telescope to view the sky. This telescope, the Iowa Robotic Telescope (IRO), is seen in the photograph of Figure 27 [below, right]. It is a matter of great coincidence, and perhaps of irony, that this telescope can play a crucial role in the final confirmations of the small comets.

Fig 26. Iowa Robotic Telescope Building Fig 27. Iowa Robotic Telescope

This will not be the first search of the sky for small comets with a ground-based telescope. About 10 years ago Clayne Yeates, a scientist at the Jet Propulsion Laboratory in Pasadena, California designed a very Fig 28. Skeet shooting the small comets clever way of detecting the small comets with the Spacewatch Telescope of the University of Arizona. His method relied upon passage of small comets by the Earth in an organized stream as inferred from the motions of atmospheric holes observed with Dynamics Explorer 1. Clayne, like so many other scientists in the 1980s, did not believe that the small comets existed. His technique to detect these small, dark, fast objects is shown in Figure 28 [left]. Telescopes are traditionally pointed so that they are staring at the stars. In order to see the small comets Clayne used the telescope in a "skeet shooting" manner. In other words, the telescope's pointing was moved in such a way as to keep the small comets in the sights of the telescope for a sufficiently long time that they would be recorded in the images.

To Clayne's surprise he in fact did find the small comets in his images and in numbers that were predicted from the observations of atmospheric holes. The small comets were clearly detected in the images. Astronomers insisted that the comets should be detected in two consecutive photographs. Clayne returned to the telescope and gained these pairs of images of each small comet. Astronomers returned with the ridiculous demand that they now needed three images. The small comets were there and the astronomers of the Spacewatch Telescope could only offer the now familiar "camera noise" as a defense. Because of his untimely death Clayne was not able to continue his brilliant applications of ground-based telescopes in the pursuit of small comets.

The Iowa telescope is now being used to verify the existence of the small comets. The initial images already are being carefully scrutinized. In Fig 29. IRO Observing Plan order to prevent any further claims of "camera noise" the image of a small comet is taken with two exposures in the same picture. This simple method is shown in Figure 29 [right]. The small comet is moving in the telescope's view. A CCD sensor is placed at the focus of the telescope in order to record the image. These sensors are found in many of the present-day video cameras although the sensor in the Iowa telescope has some special design features. In order to distinguish a real comet signal from "camera noise" two exposures are taken with a mechanical shutter. One of the exposures is twice as long as the other and these exposures are separated by a shutter closed time equal to the short exposure time. The result for detection of a single small comet is two trails, one about twice as long as the other and separated by a gap with no trail. This is shown in the lower part of Figure 29. The ratios are not quite exact because of the small blurring due to the telescope's resolution. Also you will note that the trails are shown as dark, rather than bright trails. This inversion of dark and bright is done because the human eye can detect the events more easily in the images.

Fig 30. IRO Image of Small Comet? An early candidate image of a small comet which was taken on October 19, 1998 is shown in Figure 30 [right]. The mottled appearance of the image is indeed due to camera noise. This picture is presented in order to provide the reader with an accurate accounting of the difficulties in detecting the presence of these small dark comets, and the reasons why these objects were not previously discovered by accident with ground-based telescopes. At the lower border of the photograph is the dark trail of a star. In the center of the image are the two trails of a single small comet.

The analysis of the image proceeds by verifying that the trails conform to the very demanding restraints. The results of the analysis are shown in Figure 31 [left]. It is very exciting to find the trails recorded by more than 200 individual photoelectric eyes, or "picture Fig 31. Diagram of Figure 30's Details elements", of the CCD conform to the expectations from the special shutter operation. It would take billions of such pictures before a "noise event" of this type would occur. We are well on our way for the final confirmation of the existence of small comets. A large number of such detections is necessary to complete the confirmation.

Closing comments. I would like to note that it seems almost incredible that two scientists, John Sigwarth and myself, from the University of Iowa have participated in the four major milestones in the discovery of small comets. Briefly these milestones are as follows.

1986 Initial detection of small comet impacts into the atmosphere with the Iowa camera on Dynamics Explorer 1
1989 Direct sightings of small comets with the Spacewatch Telescope of the University of Arizona
1997 Confirmation of atmospheric impacts and discovery of disrupting comets with the Iowa cameras on the Polar spacecraft
1999 Current search for small comets with the Iowa Robotic Observatory in Arizona

The scientific debate concerning the existence of small comets has been characterized by intense intellectual and emotional turmoil. I often recall the droll statement attributed to the famous physicist Max Planck who had also experienced considerable criticism from his colleagues.

"Scientists don't change their minds,
they just die."
[Next Page]


Presidential Lecture, Part 1