In 1961 he began working for the NASA Planetary Quarantine Division in an exobiology program that sought to determine the presence of microbes in outer space.
He immigrated to Israel in 1986, serving as chair of epidemiology and public health and professor emeritus at Ben-Gurion University of the Negev and director of that school's Lord Jacobovitz Center for Jewish Medical Ethics until 2009.
[1] As a condition for receiving his scholarship, he then entered an officer training program, but quit after less than a year to pursue his doctorate in bacteriology at the University of Minnesota.
He later said: "I wasn't a physician, but they asked for help so I advocated a return to the old protocols of Semmelweis and Nightingale: wash your hands, wear gowns, isolate patients.
[3] When the staph outbreak spread northward, the University of Minnesota received a $1 million grant to conduct research on it, and invited Greene to join its faculty as an assistant professor.
[1][9] In 1961 Greene was hired by NASA's Planetary Quarantine Division to head an astrobiology project in conjunction with the search for life on Mars.
[3] Living in Minneapolis, the Greenes enrolled their children in a small Torah day school to ensure they received a Jewish education.
[8] When Greene began asking questions about how religious Jews reconcile the theory of evolution with the Genesis creation narrative, the shaliach introduced him to the Lubavitcher Rebbe, Rabbi Menachem Mendel Schneerson, who had studied science and mathematics at the university level in Berlin and Paris.
[2] In 2017, the Tzeirei Hashluchim produced an animation of Greene's first meeting with the Chabad shaliach for the purpose of instructing youngsters in shlichus work.
[1] In 1986, he and his wife immigrated to Israel, where he accepted a professorship in public health and epidemiology at the university and also served as director of the school's new Jewish medical ethics program.
[3][5] The latter position saw him participate in a 1989 conference organized by bioethicist Arthur Caplan, which was the first to discuss the ethics of using data from Nazi human experimentation in modern-day scientific research.
[11] Greene lectured around the world on the compatibility between Torah teachings and scientific knowledge,[2][5] and had a morning talk show program on public television.
[9] In 1983 Greene received a Bush Foundation fellowship and was named a Senior Fulbright Lecturer by the Council for International Exchange of Scholars.