Harrison Schmitt cancelled in September 1970, the community of lunar geologists supporting Apollo felt so strongly about the need to land a professional geologist on the Moon, that they pressured NASA to reassign Schmitt to a remaining flight. As a result, Schmitt was assigned in August 1971 to fly on the last mission, Apollo 17, replacing Joe Engle as Lunar Module Pilot. Schmitt landed on the Moon with commander Gene Cernan in December 1972. Schmitt claims to have taken the photograph of the Earth known as "The Blue Marble", possibly one of the most widely distributed photographic images in existence. NASA officially
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