To Loeb, the most plausible explanation was as obvious as it was sensational: taken together with its possibly pancakelike shape and high reflectivity, ‘Oumuamua’s anomalous acceleration made perfect sense if the object was in fact a light sail—perhaps a derelict from some long-expired galactic culture. Primed by years spent pondering how we might someday find evidence of cosmic civilizations in the sky’s depths, he became increasingly convinced that, with ‘Oumuamua, the evidence had instead found us. In late 2018 Loeb and his co-author Shmuel Bialy, a Harvard postdoctoral fellow, published a paper in the Astrophysical Journal Letters arguing that ‘Oumuamua had been nothing less than humanity’s first contact with an artifact of extraterrestrial intelligence.

The paper has been a smash hit with journalists but has fallen flat with most of Loeb’s astrobiology-focused peers, who insist that, while strange, ‘Oumuamua’s properties still place it well within the realm of natural phenomena. To claim otherwise, Loeb’s critics say, is cavalier at best and destructive at worst for the long struggle to remove the stigma of credulous UFO and alien-abduction reports from what should unquestionably be a legitimate field of scientific inquiry.