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
John Young (astronaut) Module, the Apollo Lunar Module, and the Space Shuttle. In 1965, Young flew on the first manned Gemini mission, and commanded another Gemini mission the next year. In 1969 during Apollo 10, he became the first person to fly solo around the Moon. He drove the Lunar Roving Vehicle on the Moon's surface during Apollo 16, and is one of only three people to have flown to the Moon twice. He also commanded two Space Shuttle flights, including its first launch in 1981, and served as Chief of the Astronaut Office from 1974 to 1987. Young retired from NASA in