In science, alumni include astronomers Carl Sagan, a prominent contributor to the scientific research of extraterrestrial life, and Edwin Hubble, known for "Hubble's Law", NASA astronaut John M. Grunsfeld, geneticist James Watson, best known as one of the co-discoverers of the structure of DNA, experimental physicist Luis Alvarez, popular environmentalist David Suzuki, balloonist Jeannette Piccard, biologists Ernest Everett Just and Lynn Margulis, computer scientist Richard Hamming, the creator of the Hamming Code, lithium-ion battery developer John B. Goodenough, mathematician and Fields Medal recipient Paul Joseph Cohen, and geochemist Clair Cameron Patterson, who developed the uranium-lead dating method into lead-lead dating. Nuclear physicist and researcher Stanton Friedman, who worked on some early projects involving nuclear-powered spacecraft propulsion systems, is also a graduate (M.Sc).