In 1975, UFO investigator Ted Phillips published Physical Traces Associated with UFO Sightings, a catalog of landing cases in which alleged UFO encounters were followed by measurable changes to the ground, vegetation, soil, or surrounding environment. Phillips organized the cases by trace type — including circular sites, rings, “nests,” imprints, vegetation damage, residues, craters, removed soil, and footprints — and illustrated many with photographs, sketches, site diagrams, and laboratory...