Apollo 15 astronauts collected tiny green glass beads from the Moon in 1971; more than 35 years later scientists found evidence of water inside, changing what we knew about the lunar interior
In 1908, something exploded in the sky over Siberia with hundreds of times the energy of the Hiroshima bomb, flattening more than 2,000 square kilometres of forest. When scientists finally reached the site years later, they found no crater at all