A nuclear chemist, Arnold worked with University of Chicago chemist Willard Libby to develop radiocarbon dating; Libby later was awarded the Nobel Prize for the process. Arnold later moved to Princeton, and then to the University of California in San Diego where, in 1960, he established the school’s chemistry department. In 1961, he heard President Kennedy announce the goal of “landing a man on the moon and returning him safely to the Earth” before the decade was out. Arnold realized that the “space race” was more political than scientific, and he (along with three colleagues — they were dubbed the “Four Horsemen”) urged NASA to pay more attention to the science of the mission — to think of the implications of the rocks and soil samples the astronauts would gather. Those would be “not just souvenirs but the subject of important scientific investigation,” said Gerald Wasserburg, emeritus professor of geology and geophysics at Caltech. “He was a sound and resolute fighter on behalf of doing science” on the trips to the moon.
NASA listened, and more care was given to Apollo’s scientific objectives. In all, more than 800 pounds of moon rocks and soil were gathered by six Apollo crews, and the last Apollo moon mission even had a geologist on board, giving the crew the knowledge to understand which rocks should be gathered. And because of that attention — and detailed analysis of those samples — we now know the moon is rich in water, as well as precious minerals. And more: the samples tell us “how to understand why our solar system got here, and ultimately perhaps whether our sun and planets are typical of the stars we see at night, or whether we are rare, or whether we are alone,” Arnold said in 1989. “Every few years some breakthrough is possible because these rocks are available to science,” said Caltech geochemistry professor Donald Burnett. Arnold died from complications of Alzheimer’s disease on January 6, but his death wasn’t made public until this week. He was 88.