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
Michael Collins (astronaut) astronaut who had already flown a mission, and that on flights with a LM, the CMP should also have some spaceflight experience, something Anders did not yet have. Collins was therefore moved to the CMP position on the Apollo 8 prime crew, and Anders became the LMP. The policy became that the CMP would be the next most senior member of the crew, and that they would go on to command later Apollo flights. Staff meetings were always held on Fridays in the Astronaut Office and it was here that Collins found himself on January 27, 1967. Don Gregory was