April 14, 2020 By Paul Voosen Science Magazine
Late in 2018, just after its arrival in orbit, NASA’s ICESat-2 satellite passed over an iconic site from the atomic age. By chance, its laser altimeter, used mostly to measure the changing height of polar ice, bounced light off the exposed rocks of Bikini Atoll in the South Pacific Ocean, home to 23 nuclear weapons tests. Then, mission scientists looked closer: To their surprise, the laser was also generating underwater reflections.