Los Alamos green fireball, 20 December 1948

The 20 December 1948 sighting at Los Alamos was logged in a sightings table of the 17th District Office of Special Investigations as item 14. It listed four observers rated reliable, a time of 2054, a pale green or bluish white ball of basketball size, and a duration of 1-1/2 seconds. The object was recorded as disappearing behind a mountain. An FBI copy of a similar summary carried the same type of table.

Lincoln LaPaz, director of the University of New Mexico Institute of Meteoritics, reported to Lt. Col. Doyle Rees on 30 December 1948. He wrote that two pairs of Los Alamos observers had seen the fireball at 8:54 p.m.: AESS Inspectors Wilson, Truett and Strang, and Physical Security Inspector Skipper. LaPaz took transit observations with Captain M. E. Dee on 29 December. He judged the path deserved considerably less weight than the 12 December path because the baseline was only 8 miles.

LaPaz calculated that the fireball appeared at a height of at least 10 miles and descended at about 45 degrees, then levelled off and travelled about 7.5 miles nearly horizontally. Only Truett saw the descending part. LaPaz noted that no sound was heard and stated that the object was not a falling meteorite. A separate note said that the 13 and 20 December incidents involved two red lights trailing the green fireball and a sharp change of direction in the vertical plane.

In a memo to Rees dated 20 December 1948, LaPaz listed differences between the green fireballs and genuine meteors. These included the absence of noise, instant full brightness, approach from the north half of the sky, and no train of sparks or dust cloud. He wrote that the 12 December fireball was definitely non-meteoric. At the 16 February 1949 Los Alamos conference, LaPaz said a photographic patrol was set up on 19 December and nothing was observed that night. He said the 20 December incident might have been photographed, but the equipment had been disbanded and nothing was obtained.