On October 19, 2017, astronomers made the first-ever detection of an interstellar object (ISO) passing through our solar system. Designated 1I/2017 U1 ′Oumuamua, this object confounded astronomers who could not determine if it was an interstellar comet or an asteroid. After four years and many theories (including the controversial "ET solar sail" hypothesis), the astronomical community appeared to land on an explanation that satisfied all the observations.