Back in 2017 we were visited by aliens. Except no not really. But maybe? That was the year the interstellar object that came to be known as Oumuamua visited our solar system and did some very strange stuff, vectorwise. It seemed to decelerate on its approach, and accelerate as it left. Do natural bodies do that  sort of thing? Opinions vary. Here’s more from Astronomy Now:

Without the coma or dust tail of a typical comet, and with an unusual shape somewhere between a cigar and a pancake, the unresolved body resembled an asteroid of some sort more than a comet. The observed acceleration was even more mysterious, leading to widespread speculation and even suggestions the object might be some sort of alien spacecraft.

It turns out there’s a much more mundane explanation that answers most, if not all, the questions ‘Oumuamua raised: outgassing hydrogen, a mechanism likely common among icy comets moving into the warmth of the Sun. No alien technology necessary.

See more!