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
NASA Astronaut Group 4 natural sciences or engineering was a prerequisite for selection), with NASA providing pilot training as necessary. Initial screening of applicants was conducted by the National Academy of Sciences, which characterized the pool as "disappointing." Of the six ultimately chosen, four had military experience, with Garriott having previously completed the USAF Pilot Training Program. Schmitt, a geologist, walked on the Moon, while Garriott, Gibson and Kerwin all flew to Skylab. Garriott also flew on the Space Shuttle. Graveline and Michel left NASA without flying in space. NASA Astronaut Group 4 Astronaut Group 4 (The Scientists) was a group of six astronauts