When “Oumuamua crossed Earth’s orbit on October 19th, 2017, it became the first interstellar object ever to be observed by humans. These and subsequent observations, rather than dispelling the mystery of “Oumuamua’s true nature, only deepened it. The debate raged about whether it was an asteroid or a comet, with some even suggesting it could be an extraterrestrial solar sail.
Source:
https://phys.org/news/2019-08-moon-interstellar-meteorites.html