|Definition||Green fireballs and/or the Cold War|
|Signature||Green fireballs sighted in the sky from 1948 onwards|
Green fireballs are a type of unidentified flying object which have been sighted in the sky since the late 1940s. Early sightings primarily occurred in the southwestern United States, particularly in New Mexico. They were once of notable concern to the US government because they were often clustered around sensitive research and military installations, such as Los Alamos and Sandia National Laboratory, then Sandia base. Furthermore, the strange green balls of light appeared suddenly and were reported many times per month near such New Mexico installations, but hardly anywhere else.
Meteor expert Dr. Lincoln LaPaz headed much of the investigation into the fireballs on behalf of the military. LaPaz's conclusion was that the objects displayed too many anomalous characteristics to be a type of meteor and instead were artificial, perhaps secret Russian spy devices. The green fireballs were seen by many people of high repute including LaPaz, distinguished Los Alamos scientists, Kirtland AFB intelligence officers and Air Command Defense personnel. A February 1949 Los Alamos conference attended by aforementioned sighters, Project Sign, world renowned upper atmosphere physicist Dr. Joseph Kaplan, H-bomb scientist Dr. Edward Teller, other scientists and military brass concluded, though far from unanimously, that green fireballs were natural phenomena. To the conference attendees, only the green fire ball source was unknown, their existence was unquestioned. Secret conferences were convened at Los Alamos to study the phenomenon and in Washington by the U.S. Air Force Scientific Advisory Board.
In December 1949 Project Twinkle, a network of green fireball observation and photographic stations, was established but never fully implemented. It was discontinued two years later, with the official conclusion that the phenomenon was probably natural in origin.
Green fireballs have been given natural, man-made, and extraterrestrial origins and have become associated with both the Cold War and ufology. Because of the extensive government paper trail on the phenomenon, many ufologists consider the green fireballs to be among the best documented examples of unidentified flying objects (UFOs).
Early green fireballs 
Some early reports came from late November 1948, but were at first dismissed as military green flares. Then on the night of December 5, 1948, two separate plane crews, one military (Air Force C-47, Captain Goede, 9:27 p.m., 10 miles (16 km) east of Albuquerque) and one civilian (DC-3, Pioneer Flight 63, 9:35 p.m., east of Las Vegas, New Mexico), each asserted that they had seen a "green ball of fire"; the C-47 crew had seen an identical object 22 minutes before near Las Vegas. The military crew described the light as like a huge green meteor except it arched upwards and then flat instead of downwards The civilian crew described the light as having a trajectory too low and flat for a meteor, at first abreast and ahead of them but then appearing to come straight at them on a collision course, forcing the pilot to swerve the plane at which time the object appeared full moon size.
In addition, on the same night, a dozen green fireballs were seen traveling generally north to south between 7:30 p.m. and 11:30 p.m. by security guards at military installations in the vicinity of Albuquerque and Las Vegas, New Mexico. The sightings near Albuquerque were at Sandia base, a highly sensitive installation where atomic bombs were assembled near Kirtland Air Force Base. The next night, a similar green light was again spotted for a few seconds over Sandia base.
The following day, the U.S. Air Force Office of Special Investigations (AFOSI) at Kirtland AFB began an official inquiry, fearing the fireballs might be related to espionage and sabotage.
Two AFOSI investigators — both of whom were experienced pilots themselves — witnessed a green fireball while flying an aircraft the evening of December 8. They said it was about 2,000 feet (610 m) above their craft, roughly resembling the green flares commonly used by the Air Force, though "much more intense" and apparently "considerably brighter." The light seemed to burst into full brilliance almost instantaneously. Their report stated that the light was "definitely larger and more brilliant than a shooting star, meteor or flare." The light lasted only a few seconds, moving "almost flat and parallel to the earth". The light's "trajectory then dropped off rapidly" leaving "a trail of fragments reddish orange in color" which then fell towards the ground.
The next day, AFOSI consulted Dr. Lincoln LaPaz, an astronomer from the University of New Mexico and a world renowned meteor expert who had previously worked on top-secret military projects. LaPaz himself saw a "green fireball" on December 12, which was also seen at Los Alamos Scientific Laboratory, enabling LaPaz to determine the trajectory using triangulation. From this LaPaz discovered that the center of the trajectory was straight over Los Alamos.
In a classified letter to the Air Force on December 20, LaPaz wrote that the object moved far too slowly to have been a meteor and left no "trail of sparks or dust cloud" as would be typical of meteors flying at low altitudes. Other anomalous characteristics were the intense lime-green color (completely unlike the Geminids meteor shower being observed at the same time), low altitude of only 8–10 miles yet exhibiting no sound, flat rather than arced trajectory, and turning on and off like a light switch. Later, he was to add that the sightings were confined almost entirely to northern New Mexico, and no fragments were ever found despite extensive searches using triangulation techniques that had previously been successful in locating meteor fragments.
LaPaz suggested that security patrols at Los Alamos should attempt to photograph the green fireballs. However, the duration of the fireballs was so brief (1–5 seconds) and the onset so unexpected that photography was unsuccessful. Other green fireball sightings occurred over Los Alamos on December 11, 13, 14, 20, 28, and January 6, 1949, raising the level of concern of security and military intelligence. The green fireball on December 20 was most remarkable in that it was seen to change direction, quite impossible for a meteor. Two security guards saw it first descending at a 45-degree angle, then leveling off at an altitude of about two miles (3 km). Even though at most only a few miles distant, no sound was heard, just as with the other green fireballs.
On January 13, 1949, the following message was sent to the Director of Army Intelligence from Fourth Army Headquarters in Texas: "Agencies in New Mexico are greatly concerned . . .Some foreign power [may be] making 'sensing shots' with some super-stratosphere device designed to be self-disintegrating . . . The phenomena [may be] the result of radiological warfare experiments by a foreign power . . . the rays may be lethal or might be . . . the cause of the plane crashes that have occurred recently . . . These incidents are of such great importance, especially as they are occurring in the vicinity of sensitive installations, that a scientific board [should] be sent . . . to study the situation."
On January 30 the brightest and most widely seen green fireball sighting occurred near Roswell, New Mexico. The next day, the FBI was informed by Army and Air Force intelligence that flying saucers and the fireballs were classified top secret. LaPaz interviewed hundreds of witnesses, with help from the FBI and military intelligence, and again tried to recover fragments by triangulating a trajectory, but was again unsuccessful.
After his own sighting and interviewing numerous witnesses, LaPaz had concluded that "green fireballs" were an artificial phenomenon. On February 8 he met with Dr. Joseph Kaplan, a UCLA geophysicist and member of the Air Force Scientific Advisory Board. Kaplan, himself a meteor expert, agreed they could not be conventional meteorite falls and informed LaPaz that he knew of no secret military projects that could explain the fireballs. He found LaPaz's data on the fireballs unsettling and felt an investigation was needed in the name of national security.
LaPaz's informal scientific study for the Air Force quickly became formal, being called the "Conference on Aerial Phenomena", convening at Los Alamos Scientific Laboratory in mid-February to review the data. The assembled people—both military personnel and civilian scientists—were informed by LaPaz that the fireballs were not the result of any secret military project, according to Dr. Kaplan. LaPaz reiterated that he was absolutely convinced the green fireballs were not conventional fireballs or meteorites. Dr. Edward Teller felt they could not be material objects because they made no sound and suggested they might be some unknown atmospheric electrical phenomena. In any event, he thought they could not be foreign probes of some kind.
The scientists felt that a network of instrument stations should be established to photograph and analyze the fireballs. Despite the recommendation and the continuation of the green fireballs at a rate of about half a dozen a month, LaPaz and AFOSI oddly encountered both resistance and apathy from Air Force authorities responsible for setting up such a network.
By April 1949 similar sights were reported over a nuclear-weapons storage facility at Fort Hood in Texas. The intrusions were deemed so serious that, unlike the Air Force, the Army quickly set up an observation network. Sightings continued through August, the most spectacular being on June 6 when a hovering orange light, 30 to 70 feet (21 m) across and a mile in the air, was spotted. Finally, it started moving in level flight and then burst into small particles.
On July 24 a green fireball was observed falling close to Socorro, New Mexico. Dust samples were collected at the School of Mines there and were found to contain large particles of copper. LaPaz found this highly significant, since copper burns with the same yellow-green color characteristic of the green fireballs. He also noted that if the copper particles came from the green fireballs, then they could not be conventional meteorites, since copper was never found in dust of meteoric origin. LaPaz suggested that further air and ground samples be taken in areas where the fireballs were seen.
At the same time, AFOSI informed LaPaz on investigations of "anomalous luminous phenomena" between early June and early August. Many of the green fireballs were now descending on vertical paths, whereas initially they almost always traveled horizontally.
Another Los Alamos conference convened on October 14. No one disputed the reality of the phenomena and nobody could explain it. Among the puzzles were the sudden onset and the high concentration of sightings in New Mexico, quite unlike natural phenomena. Despite this, it was decided the fireballs were probably atmospheric in origin. Instrumented observations—photographic, triangulation, and spectroscopic—were deemed essential to solving the mystery.
On November 3 Dr. Kaplan brought the plan to the Air Force Scientific Advisory Board at the Pentagon. Kaplan by this time had decided the fireballs might be a new type of rare meteor. Nonetheless, most of the scientists remained puzzled by the brightness, trajectories, and absence of sound. Seeming to contradict his meteor hypothesis, Kaplan also said, "This high selectivity of direction seems to indicate that some group was trying to pinpoint Los Alamos with a new sort of weapon." Concerns were expressed about the possibility of panic and the need for continued secrecy.
Project Twinkle 
Finally, on December 20 after nearly a year of foot-dragging, the instrument observation program was approved and Project Twinkle was born. The first instrument post (consisting of two officers) was established at Holloman Air Force Base in February 1950. Only one other instrument post was ever set up. LaPaz criticized Project Twinkle as inadequate, arguing the green fireballs were worthy of "intensive, systematic investigation". Twinkle did manage to record a few events, but the data collected were said to be incomplete in the final Twinkle report. Besides, it was stated, no funding had been provided for follow-up data analysis. In addition, the fireball activity near the observation posts seemed to virtually disappear, as noted in a report from September: "It may be considered significant that fireballs have ceased abruptly as soon as a systematic watch was set up."
Over the objections of LaPaz and others, the final report on Project Twinkle (see external links) concluded the green lights were probably a natural event, maybe sunspot activity or an unusual concentration of meteors. The report stated, "There has been no indication that even the somewhat strange observations often called 'Green Fireballs' are anything but natural phenomena." Twinkle was discontinued in December 1951.
Despite efforts of the final Twinkle report to downplay the fireballs and other studied UFO phenomena as natural, a follow-up report in February 1952 from the USAF Directorate of Intelligence disagreed:
- "The Scientific Advisory Board Secretariat has suggested that this project not be declassified for a variety of reasons, chief among which is that no scientific explanation for any of the fireballs and other phenomena was revealed by the report and that some reputable scientists still believe that the observed phenomena are man-made."
It was also stated that some of the scientists continued to believe they were Russian spy devices. Besides LaPaz, this included Dr. Anthony Mirarchi, the first director of Project Twinkle.
The following month, another letter from the Directorate of Intelligence to the Research Division of the Directorate of Research and Development again stated that the report should not be publicly released, since no real solution had been provided:
- "It is believed that a release of the information to the public in its present condition would cause undue speculation and give rise to unwarranted fears among the populace such as occurred in previous releases on unidentified flying objects. This results from releases when there has been no real solution."
Opinions of Los Alamos scientists 
Edward J. Ruppelt, director of the USAF Project Blue Book UFO study, stated he visited the Los Alamos National Laboratory in early 1952 and spoke to various scientists and technicians there, all of whom had experienced green fireball sightings. None of them believed they had a conventional explanation, such as a new natural phenomenon, secret government project, or psychologically enlarged meteors. Instead, the scientists speculated that they were extraterrestrial probes "projected into our atmosphere from a 'spaceship' hovering several hundred miles above the earth." Ruppelt commented, "Two years ago I would have been amazed to hear a group of reputable scientists make such a startling statement. Now, however, I took it as a matter of course. I'd heard the same type of statement many times before from equally qualified groups."
However, such opinions were apparently not unanimous. Immediately afterward, Ruppelt said he visited LaPaz in Albuquerque. Ruppelt reported that "LaPaz said that some people, including Dr. Joseph Kaplan and Dr. Edward Teller, thought that the green fireballs were natural meteors. But he didn't think so." LaPaz then reiterated the various anomalous characteristics which led him to believe the fireballs were artificial. Ruppelt also mentioned that he had previously met with Kaplan earlier in Los Angeles, and although Kaplan respected LaPaz professionally, he was not convinced that the fireballs were man-made.
Ruppelt further mentioned that he discussed the issue with some of the people who had been at the Los Alamos meeting in February 1949, but did not provide any names. "People who were at that meeting have told me that Dr. LaPaz's theory was very interesting and that each point was carefully considered. But evidently it wasn't conclusive enough because when the conference broke up, after two days, it was decided that the green fireballs were a natural phenomenon of some kind." However, despite what Ruppelt may have been told and then reported in his book, there is nothing in the actual transcript of the conference that indicates that such a group decision was ever reached. Instead, opinions remained divided, much puzzlement was expressed, and further research was recommended to help resolve the issue.
Astronomer sightings of green fireballs 
Other astronomers besides LaPaz known to have sighted green fireballs in New Mexico during this period were Clyde Tombaugh, who in 1956 said he had seen three, and Dr. Donald Menzel, who sighted one in May 1949 near Alamogordo. In a letter to the Air Force Scientific Advisory Board, Menzel admitted the phenomenon must be real and expressed puzzlement, wondering why the fireballs should be so confined to New Mexico if they were natural phenomena. Menzel eventually became a famous UFO debunker, and in two of his books stated he was never puzzled by his sighting, instantly identifying the object as an ordinary meteor fireball.
Green fireballs after Project Twinkle 
Despite the discontinuation of Project Twinkle, green fireballs were still occasionally sighted and LaPaz continued to comment. In early November, 1951, a month before the official termination of Twinkle, a huge flurry of green fireball sightings occurred in the Southwest and other states. LaPaz was widely quoted saying that such a concentration of fireballs was unprecedented in history, and he didn't believe they were a natural phenomenon. (more details below in Atomic testing and fallout theory) In April 1952 the green fireballs and Project Twinkle were written up in a famous Life magazine article titled "Have We Visitors From Space?" A recent green fireball incident over Arizona from November 1951 was mentioned. LaPaz again repeated why the fireballs could not be ordinary meteors. The article also described LaPaz's UFO sighting near Roswell, New Mexico, on July 10, 1947, about the same time as the famous Roswell UFO incident. LaPaz, however, remained anonymous. Also described was a 1949 UFO sighting by astronomer Clyde Tombaugh, the discoverer of Pluto (Life magazine article).
In January 1953 LaPaz was quoted in newspaper articles saying the green fireballs were artificial devices and might be a Soviet missile scouting the U.S. and other parts of the world. According to Ruppelt, the green fireballs reappeared in September 1954. One the size of a full moon was seen streaking southeast across Colorado, lighting up Denver, and into northern New Mexico. It was seen by thousands at a football stadium in Santa Fe. LaPaz was called back in to investigate, but told a reporter that he did not expect to find anything. From April 3 to 9, 1955, five green fireballs were reported in New Mexico and two in northern California. At least three were reported within minutes of one another midmorning of April 5. LaPaz stated, "This is a record . . . I'm sure the yellow-green fireballs aren't ordinary meteorite falls. I've been observing the skies since 1914, and I've never seen any meteoritic fireballs like them." In a visit by astronomer Dr. J. Allen Hynek in March 1965, LaPaz told Hynek that one had been reported as recently as the previous Christmas (Steiger, p. 132).
Atomic testing and fallout theory 
A recent theory of the green fireballs was introduced in Robert Hastings' 2008 book UFOs and Nukes. Although it had been a concern from the beginning to military intelligence that the sightings seemed concentrated near sensitive nuclear facilities such as Los Alamos and Kirtland AFB, researcher Dan Wilson discovered that later heavy concentrations of sightings might also be correlated with atomic tests that began in Nevada in January 1951. In particular, green fireball sightings, and other reported UFO sightings, seemed to follow the drift of the fallout clouds as winds carried them into other states.
Hastings cites a number of examples from Wilson's research. Perhaps the most graphic example occurred during the "Buster series" of atomic tests on November 1 and 5, 1951, which were accompanied by so many reported green fireball sightings in states affected by fallout, that even the New York Times carried a story on November 9, "Southwest's 7 Fireballs in 11 Days Called 'Without Parallel in History'." Dr. LaPaz was widely quoted saying, "There has never been a rate of meteorite fall in history that has been one-fifth as high as the present fall. If that rate should continue, I would suspect the phenonenom is not natural... [they] don't behave like ordinary meteorites at all."
Initially the green fireballs were reported in Arizona and New Mexico as the fallout clouds left Nevada, but as the clouds spread out and drifted further east, south, and north, green fireball sightings then followed in Texas, northern Mexico, Iowa, Kansas, Indiana, Michigan, and New York. Portions of the fallout also drifted west into the Los Angeles area on November 7, followed the next day by a green fireball sighting there.
Time magazine also took note on November 19, in a somewhat satirical article titled "Great Balls of Fire." In the article, they lightheartedly speculated that the green fireballs were connected to the atomic testing.
Summarizing the rash of fireball sightings in November 1951, Wilson commented, "Some researchers imply that the radioactivity itself was producing the green fireballs, possibly as an electrostatic effect. Dr. Lincoln La Paz thought otherwise. He said that the green fireballs move too regularly and had been sighted earlier, on a number of occasions, at the Los Alamos and Sandia atomic labs, where no measurable radiation was released, as well as at Killeen Base, in Texas, where the weapons were simply stored. So it seems that the electrostatic theory doesn't stand up."
Wilson concluded, "We can make one statement of fact: the fireball sightings—green or otherwise—occurred in areas that received radioactive debris from Operation Buster. Was this just coincidence, or a planned occurrence? We simply don't know, so all we can do is to continue to collect data and see if some overwhelmingly convincing pattern emerges." Wilson nonetheless felt the evidence pointed to the fireballs being real, artificial, and those responsible having some sort of agenda." 
Hastings then noted similar comments by Project Blue Book head Edward Ruppelt, citing the opinion of a number of Los Alamos scientists on the green fireballs when he visited in early 1952, that they might be extraterrestrial probes from an orbiting spacecraft. (See Opinions of Los Alamos scientists above.)
Condon Committee theory 
In the 1969 Condon Committee UFO report, astronomer William K. Hartmann thought the green fireballs might be explained by lunar material ejected during recent meteor impacts on the Moon's surface . Hartmann's reasoning was that such ejected lunar meteors could account for the abnormally low velocities calculated for the green fireballs by LaPaz of about Earth's escape velocity, that is, much lower than normal meteor velocities. Hartmann further claimed, without explanation or elaboration, that "the predicted characteristics match those of the 'green fireball episode'."
However, the fact is that an object coming from the moon would enter the earth's atmosphere with a speed almost as high as the escape velocity of the earth, 11 km/s. And the theory would not account for the many other anomalous characteristics of the green fireballs detailed by LaPaz, such as strong confinement to the New Mexico area, lime-green color, low altitude yet absence of sound, absence of smoke trail, and absence of meteorite fragments. Despite the entirely speculative nature of Hartmann's hypothesis, it is sometimes cited as scientific fact: for example, astronomer Carl Sagan presented it as such in his Cosmos television series in 1980[verification needed].
Other UFO Investigations of Dr. Lincoln LaPaz 
Roswell Incident (1947) 
At least three witnesses, including two involved with Army and Air Force counterintelligence, also claimed that LaPaz was brought in after the Roswell UFO incident to interview witnesses and reconstruct the trajectory of the crash object (affidavit of one witness). One counterintelligence agent claimed LaPaz told him he thought the object got into trouble, touched down for repairs, took off again, and then exploded. The two of them then speculated about possible origins. LaPaz allegedly held the opinion that the object was an unoccupied extraterrestrial probe.
However, UFO researcher Karl T. Pflock discovered some facts that might call into question some aspects of this testimony. For example, one of the purported witnesses to LaPaz's Roswell involvement claimed that LaPaz spoke fluent Spanish, but by interviewing family members, Pflock discovered that LaPaz did not speak any Spanish.
Anomalous satellites (mid-1950s) 
Besides LaPaz's consultations with the Air Force on the green fireballs, in 1954 he was also involved with astronomer Clyde Tombaugh in a search for near-Earth orbiting satellites on behalf of the Army (several years before Sputnik became the first man-made satellite). In August 1954 a story broke in the press that Tombaugh and LaPaz had found two of the satellites only 400 and 600 miles (970 km) out that had recently come into orbit. But LaPaz later denied the report. (See Clyde Tombaugh for details.)
Zamora/Socorro Incident (1964) 
In 1964 LaPaz was also involved peripherally in the investigation of the famous Socorro UFO incident, in which a Socorro policeman named Lonnie Zamora claimed to have seen a small egg-shaped object land, saw two humanoid figures near the object, and then when he approached to within 50 feet (15 m), the object blasted off and rapidly disappeared. LaPaz interviewed Zamora and vouched for him as a witness.
Green fireballs revisited (1965) 
LaPaz's last known comments on the green fireballs occurred in 1965 during a visit by astronomer Dr. J. Allen Hynek, a consultant to the Air Force's Project Blue Book. Hynek was also investigating the Socorro incident. According to Hynek, LaPaz felt the fireballs were the most important part of the UFO phenomenon. He remained convinced that the fireballs' anomalous characteristics had never been adequately explained by the official investigation. LaPaz continued to think the green fireballs were artificial, but now believed the fireballs, and also the Socorro craft, to be highly secret projects of the U.S. government. He also accused Hynek, Project Blue Book, and others of being part of "a grand cover-up for something the government does not want discussed".
Green fireballs outside the United States 
There have been reports of green fireballs outside the U.S. and long after the early days of Project Twinkle  often near sensitive government or military bases: Randles and Houghe note that a Royal Air Force pilot had a near collision with three unusual green fireballs near Manchester, England, and fireballs were also sighted near a nuclear power plant in Suffolk in 1983 (Randles and Houghe, p. 92). There was also a sighting of a green fireball in Cold Lake, Alberta, Canada in the summer of 2011. Cold Lake notably has the largest air force base in all of Canada, and after several local protests in the 1980s, Cold Lake no longer has nuclear weapons.
See also 
Green fireball sighting - Date: November 15th 2012 Time: 8:47pm PST Location: Lonsdale and West 4th st, North Vancouver,BC Seen by Michael Muise
- Page 47, Ruppelt Edward, J. (1956) Report on Unidentified Flying Objects, DoubleDay
- Ruppelt Edward, J. (1956) "report on unidentified flying objects", DoubleDay
- Jerome, Clark (1998) "The UFO Book: Encyclopedia of the Extraterrestrial", Visible Ink Press
- Maccabee, Bruce (2000) "The UFO-FBI Connection", Llewellyn Publications
- Page 50, Ruppelt Edward, J. (1956) Report on Unidentified Flying Objects, DoubleDay
- Pages 50-51, Ruppelt Edward, J. (1956) Report on Unidentified Flying Objects, DoubleDay
- Transcript of Los Alamos conference
- Ruppelt, 78–79, 81; Clark 1998, 263; Maccabee, 149–161; , 
- Page 48, Ruppelt Edward, J. (1956) Report on Unidentified Flying Objects, DoubleDay
- Pages 47-48, Ruppelt Edward, J. (1956) Report on Unidentified Flying Objects, DoubleDay
- Ruppelt, Chapter 4
- Menzel letter, May 16, 1949, cited at an Air Force Scientific Advisory Board meeting on the green fireballs in Washington, D.C., Nov. 3, 1949. The quoted section read, "Circumstances force me to conclude that the phenomena described are actually real. With regard to Dr. Kaplan's [meteor] explanation, which deserves very serious consideration, I merely raise the question as to why the phenomenon seems to be confined to the Alamogordo region."
- For example, in contrast to his 1949 private statement to the Air Force that he didn't find the meteor explanation totally adequate, Menzel later wrote in his UFO debunking book "The UFO Enigma" (1977) with Ernest Tavres that, "He and several other astronomers present observed the bright green object as it slowly traversed the northern sector of the heavens, moving from east to west: they quickly and unequivocally identified it as a meteor, or bolide..."
- Robert Hastings, UFOs and Nukes, 2008, pp. 64-84.
- Hastings, 64-70
- Hastings, 70
- Pflock, Karl T. Roswell : Inconvenient Facts and the Will to Believe Prometheus Books, 2003
- "Scientist denies space base find". New York Times. October 10, 1954.
- Steiger, pp. 132, 136
- Blog listing modern green fireball reports from witnesses
- Jerome Clark, Unexplained! 347 Strange Sightings, Incredible Occurrences, and Puzzling Physical Phenomen, Visible Ink Press, 1993.
- Jerome Clark, The UFO Book: Encyclopedia of the Extraterrestrial, Visible Ink Press, 1998.
- Edward J. Ruppelt, The Report on Unidentified Flying Objects, 1956, Chapt. 4 
- Bruce Maccabee, The UFO-FBI Connection, Llewellyn Publications, 2000
- Brad Steiger, Project Blue Book, Ballantine Books, 1976 (Contains letter from Dr. J. Allen Hynek of Dr. LaPaz expressing final opinion on green fireballs)
- Jenny Randles and Peter Houghe; The Complete Book of UFOs: An Investigation into Alien Contact and Encounters; Sterling Publishing Co, Inc, 1994; ISBN 0-8069-8132-6
- Transcript of 1949 Los Alamos conference on green fireballs
- Project Twinkle final report
- Links to more green fireball documents
- Project Twinkle chapter from Dr. Bruce Maccabee's UFO/FBI Connection book
- Maccabee's "White Sands Proof" essay, similar but more detailed discussion of the green fireballs and critical collected evidence omitted from Twinkle final report.
- Another article on green fireballs and Project Twinkle
- 1952 Life magazine article. Discusses UFO evidence, green fireballs, and LaPaz's sightings and findings.
- Photo of a meteor with a greenish tint in tail
- Skeptical witness of a green fireball