While keeping an open mind on the possibility of interplanetary travel, Tombaugh himself has never supported the spaceship interpretation so often attributed to him in print but has considered various possible explanations--insects or birds illuminated by ground lights, or reflections of ground lights against the boundary of an inversion layer in the air. Of these, the inversion theory seems the most probable. The layer in such a case must have been extremely thin or extremely weak, otherwise it would have dimmed the brightness of the faint stars he was observing. As in the Chesapeake Bay case, the mysterious rectangles were undoubtedly the special effect of some unique combination of circumstances, unlikely to be repeated. Conditions were ideal for the formation of small sharply localized inversions: the weather was clear, the day had been hot. A small temperature inversion existing at a relatively low elevation and smoke, haze, or dust collecting in a very thin layer at a relatively low altitude were the prerequisites that almost certainly existed. Some unknown cause--in the vicinity of an airfield there are many possibilities--could have produced a ripple in the thin haze layer. This ripple, tipping the haze layer at a slight angle, could have reflected the lighted windows of a house; as the ripple progressed in a wavelike motion along the layer, the reflection would have moved as did the rectangles of light. Conditions of refraction at the interface would have reflected the wave upward. Tombaugh has recently summarized his convictions on the entire UFO phenomenon as well as on his own sighting: “From my own studies of the solar system I cannot entertain any serious possibility for intelligent life on the other planets, not even for Mars (the planet to which I have devoted considerable observation and study over the past thirty-five years). The logistics of visitations from planets revolving around the nearer stars is staggering. In consideration of the hundreds of millions of years in the geologic time scale when such visitations may possibly have occurred, the odds of a single visit in a given century or millennium are overwhelmingly against such an event. “A much more likely source of explanation is some natural optical phenomenon in our own atmosphere. In my 1949 sighting the faintness of the object, together with the manner of fading in intensity as it traveled away from zenith towards the southeastern horizon, is quite suggestive of a reflection from an optical boundary or surface of slight contrast in refractive index, as in an inversion layer. “I have never seen anything like it before or since, and I have spent a lot of time where the night sky could be seen well. This suggests that the phenomenon involves a comparatively rare set of conditions or circumstances to produce it, but nothing like the odds of an interstellar visitation.” [XII-1] Air Force Files.