The Air Force was not particularly worried about interplanetary visitors, but it was concerned with the possibility that the fireballs were man-made vehicles, a potential danger to the country. One scientist had suggested that the Russians might have constructed a guided missile whose nose cone, the final stage in a multistage rocket, was made of ice and various other chemicals. In re-entering the earth’s atmosphere, such a cone would burn up; the vaporizing ices would account for the green color observed, for the silent disappearance of the object, and for the lack of material traces on the ground. Whatever the true explanation, members of the Air Defense Command could not afford to guess; they had to know. In mid-February 1949 they assembled at Los Alamos a conference of military and intelligence officers, physicists, and astronomers, to discuss the problem of the green fireballs. After two days of studying the evidence, most of the members agreed that the fireballs were meteors of an unusual type and, as natural phenomena, not a threat to national security. To take care of the extremely remote chance that this conclusion might be wrong, the conference turned over the problem to the scientists at Air Force Cambridge Research Center which, in the late summer, organized Project Twinkle to equip and establish three cinetheodolite stations in New Mexico. Fitted with a diffraction grating to split the spectrum into its component colors (and thus identify the chemical elements present), the cameras were to photograph and record the altitude, size, speed, and spectrum of the luminous objects. Since the green fireballs, meanwhile, had all but vanished from the skies, enthusiasm for the research project diminished. Only one camera (designed by Dr. Menzel) was ever put into operation and it never found anything to photograph. After two months of futile searching, the Air Force finally abandoned Project Twinkle as a waste of time. In the years following, green fireballs occasionally appeared. An astronomer observed one over Lafayette, Colorado, at 7:45 P.M. on June 4, 1950. One soared over the New England states and eastern Canada on November 2, 1950, and a year later, on November 2, 1951, a plane crew over Texas sighted another which was dramatically publicized in _Life_ magazine, and described in another publication as a missile that ejected flaming balls. Few other fireballs made the headlines until the one of September 18, 1954, but even that caused only brief excitement and the Air Force expressed no alarm. _Meteors in the Records_