Harrison Schmitt credits the image to the entire Apollo 17 crew. While on the Moon's surface, Schmitt — the only geologist in the astronaut corps — collected the rock sample designated Troctolite 76535, which has been called "without doubt the most interesting sample returned from the Moon". Among other distinctions, it is the central piece of evidence suggesting that the Moon once possessed an active magnetic field. As he returned to the Lunar Module before Cernan, Schmitt is the next-to-last person to have walked on the Moon's surface. After the completion of Apollo 17, Schmitt played an active role in documenting the
Apollo 17 out to the Moon, back to Earth, and in lunar orbit. The Apollo 17 crew conducted an experiment, also conducted on Apollo 16, with the objective of linking these light flashes with cosmic rays. As part of an experiment conducted by NASA and the University of Houston, one astronaut wore a device that recorded the time, strength, and path of high-energy atomic particles that penetrated the device. Analysis of the results concluded that the evidence supported the hypothesis that the flashes occurred when charged particles travelled through the retina in the eye. Apollo 17 was the only lunar surface expedition