Physical trace UFO reports were labeled Close Encounters of the Second Kind (CE-II) by Dr. J.Allen Hynek and involve instances where there was a physical interaction between the UFO and its environment. Usually these involve a landing trace, such as depressed grass or soil, but also burned or broken vegetation, residues, and more exotic traces.
The program UFO Physical Trace Cases by Dr. Nicholas Platco presents 10 of the top physical traces cases-cases of high strangeness that involved multiple witnesses. The cases presented by Dr. Platco represent just 10 trace/landing events from a UFO database of over 4000 such events. Dr. Nicholas Platco is a retired Astronomy and Meteorology professor at Penn State University.