NOVA

For decades UFOs have captivated the public, even as many scientists saw them as too taboo to investigate. Now, after highly publicized sightings of unidentified objects by Navy pilots, UFOs are moving out of the shadows and into the light, as NASA pledges to study them scientifically. So what does science have to say? Though some are identified as balloons or drones, weather phenomena, or optical illusions, others remain mysterious. Could they be the result of secret new technology developed by other governments – or our own? And what would it take for alien engineers to traverse vast distances to send probes or visit Earth from other solar systems? Explore the evidence, as astrophysicists and engineers use new technologies to investigate the strangest objects in our skies.