Have probes of extraterrestrial origin conducted surveillance missions in Earth's atmosphere? James McDonald, co-founder of the Institute of Atmospheric Physics at the University of Arizona, one of the twentieth century's leading atmospheric physicists, presented strong evidence for this hypothesis at the annual meeting of the American Association for the Advancement of Science in December 1969. Yet, remarkably, McDonald's important conjecture has all but disappeared from the purview of scientists today. That's likely to soon change, former Science Museum (London) curator Tom Willamson argues...