As an immediate result of this tragic accident, Air Force officials recommended that all pilots be briefed again on the use of oxygen and the effects of lack of oxygen. New orders were issued; that no pilot go above 12,000 feet without oxygen under any circumstances; that no aircraft be cleared for cross-country flight unless it had been serviced with oxygen; that classes in the use of oxygen start immediately for all pilots and crew members; that all aircraft be equipped with oxygen; and that all pilots carry mask, helmet, goggles, and gloves on all flights. The cause of the crash was known. But investigators had still to solve the problem: what was the unknown object that Mantell had been chasing? [Illustration: _Figure 5._ UFO sightings in the Mantell case. The broken line indicates the path a balloon would have followed.] An Air Force official had announced to the press that the unknown had been the planet Venus. This explanation, while not impossible, was not very probable. The position of Venus that afternoon had indeed been very close to that of the unknown object. But with a stellar magnitude of -3.4, less than half its maximum brilliance, in the daylight sky the planet would have been visible, if at all, only as an exceedingly small, bright point of light. Furthermore this answer did not fit the pattern of sightings. The accompanying map (see Figure 5) of the Ohio-Kentucky-Tennessee region illustrates the succession of events: 1:15 P.M., Maysville, Kentucky. Strange object sighted moving west. 1:35 P.M., Owensboro and Irvington, Kentucky. Circular object sighted, 250 to 300 feet in diameter, moving west. Shortly before 1:45 P.M., Godman Air Force Base, Kentucky. Circular or parachute-shaped object sighted; in view for about two hours, slowly moving south. 4:00 P.M., Madisonville, Kentucky. Strange object; through binoculars identified as a balloon. 4:45 P.M., Nashville, Tennessee. Strange object sighted; through binoculars identified as a balloon. 5:00 P.M., Lockbourne Air Force Base, Columbus, Ohio. Round glowing amber object sighted on southwest horizon in horizontal flight; in view about twenty minutes, then disappeared below the horizon.