Jessup has been referred to in ufological circles as "probably the most original
extraterrestrial hypothesiser of the 1950s", and it has been said of him that he was "educated in
astronomy and
archeology and had working experience in both." Actual evidence of an educational background in archaeology or archaeological field work is absent from Jessup's resume, but
Jerome Clark reports that Jessup took part in archeological expeditions to the
Yucatan and
Peru in the 1920s. Jessup documented an expedition to
Cuzco he took part in during 1930. In 1923, along with University of Michigan botanist Carl D. LaRue and plant pathologist
James Weir, Jessup participated as a photographer in a
U.S. Department of Agriculture expedition to
Brazil to study the possibility of growing rubber in the Amazon.
Henry Ford would later draw on the expedition's findings, as well as the assistance of LaRue and Weir, when planning
Fordlandia, his rubber plantation in the Amazon. Jessup achieved some notoriety with his 1955 book
The Case for the UFO, in which he argued that
unidentified flying objects (UFOs) represented a mysterious subject worthy of further study. Jessup speculated that UFOs were "exploratory craft of 'solid' and 'nebulous' character." Jessup also "linked ancient monuments with prehistoric superscience"; years later similar claims were made by
Erich von Däniken in
Chariots of the Gods? in 1968 and other books. A copy of
The Case for the UFO unwittingly became the nexus of a whole other conspiracy theory when
Carl Meredith Allen (sometimes calling himself Carlos Miguel Allende), an ex-
merchant marine, sent it covered in scribbled notes to a US Navy research institute, and sent a series of letters to Jessup himself, laying out an incident Allen claimed to have witnessed during World War II where the US Navy made a ship invisible and accidentally teleported it through space, the so-called "
Philadelphia Experiment". Jessup wrote three further flying-saucer books,
UFOs and the Bible,
The UFO Annual (both 1956), and
The Expanding Case for the UFO (1957). The latter suggested that
transient lunar phenomena were somehow related to UFOs in the earth's skies. Jessup's main flying-saucer scenario came to resemble that of the
Shaver Hoax perpetrated by the science-fiction magazine editor
Raymond A. Palmer—namely, that "good" and "bad" groups of space aliens were/are meddling with terrestrial affairs. Like most of the writers on flying saucers and the so-called
contactees that emerged during the 1950s, Jessup displayed familiarity with the alternative
mythology of human prehistory developed by
Helena P. Blavatsky's cult of
Theosophy, which included the mythical lost continents of
Atlantis,
Mu, and
Lemuria. ==Death==