ʻOumuamua: A Messenger From Afar
ʻOumuamua was discovered on October 19, 2017, by astronomer Robert Weryk at Hawaii’s Haleakalā Observatory, using the Pan-STARRS1 telescope. Initially classified as an asteroid and given the designation A/2017 U1, it was soon reclassified as a comet (C/2017 U1). However, further analysis revealed it was something entirely new—an object from outside our solar system. It was ultimately named 1I/2017 U1, with "1I" marking it as the first interstellar object ever detected passing through our solar system. At the moment of its discovery, ʻOumuamua was already speeding away from Earth, about 33 million kilometers (21 million miles) distant and headed out into space. We never saw it approaching—and it was moving so fast, we almost missed it entirely.
To grasp just how fast ʻOumuamua was moving, consider this: Voyager 1—humanity’s fastest spacecraft—travels at roughly 17km/second, fast enough to make a bullet look like it’s in slow motion. ʻOumuamua, however, was clocked at an incredible 26km/second.
As it sped through space, its brightness fluctuated dramatically—by a factor of 10—indicating it was tumbling chaotically. By analyzing these light variations, astronomers were able to estimate its size and shape. What they found was extraordinary: ʻOumuamua was likely between 100 and 400 meters long and possibly up to ten times longer than it was wide. For comparison, the most elongated object ever observed in our solar system before had a length-to-width ratio of just 3:1. ʻOumuamua's extreme, cigar-like proportions were unlike anything seen before.
Coupled with its hyperbolic trajectory—meaning it wasn’t bound to the Sun’s gravity—ʻOumuamua stood out as a genuine cosmic enigma. It came from the stars, offered only the briefest glimpse, and then disappeared forever into the void.
The Plot Thickens
2I/Borisov, named after amateur astronomer Gennadiy Borisov who discovered it, holds the distinction of being the second confirmed interstellar object to enter our solar system. Unlike ʻOumuamua, Borisov looked and behaved exactly like a typical comet: a glowing nucleus trailing a broad, dusty tail. It zipped through the inner solar system and began to fragment by early 2020—eventful, yes, but entirely expected. Its predictability only served to make ʻOumuamua seem even more puzzling by contrast.
When ʻOumuamua was first discovered, it was classified as A/2017 U1, marking it as an asteroid—a rocky object drifting silently through space. But as astronomers observed it more closely, it started exhibiting an unexpected acceleration, prompting a reclassification to C/2017 U1, the "C" indicating a comet. This made sense as comets often speed up due to outgassing, where sunlight heats their icy surfaces, causing jets of gas and dust to erupt and act as a propellent, like a natural rocket. This process is also what gives comets their signature glowing tails.
But 'Oumuamua didn't have a tail. It showed no signs of outgassing, or visible emissions on any kind. Yet, it was accelerating. This anomaly sparked a whirlwind of speculation. Scientists proposed all sorts of theories—some plausible, many outlandish. But none could definitively explain how this object was moving the way it was.
Then, in September 2020, astronomers detected another fast-moving object: 2020 SO. It too was accelerating as it moved away from the Sun, yet, like ʻOumuamua, it lacked any evidence of a tail or outgassing. Initially, it seemed like a second chance at solving the mystery. But this time, the explanation turned out to be far more down-to-Earth—literally. After tracing its orbital path, astronomers concluded that 2020 SO wasn’t an interstellar visitor at all. It was a relic of human space exploration: a discarded rocket booster from NASA’s 1966 Surveyor-2 mission.
However, this discovery added a lot of fuel to an already burning conspiracy theory fire.
If a man-made object could mimic the behavior of ʻOumuamua, then could ʻOumuamua itself be artificial?
Rendezvous With Rama
When it comes to ʻOumuamua, the conspiracy theories are as numerous as they are imaginative. While it's impossible to cover them all, the most popular are those that believe 'Oumuamua was our first encounter with alien technology.
One of the most prominent theories suggests that ʻOumuamua wasn’t a natural object at all, but a spacecraft—or at least a fragment of one. Similar to 2020 SO, some speculate that 'Oumuamua is the alien equivalent to NASA space junk and is a broken-off piece of a larger structure. Supporters of this idea point to its chaotic tumbling across multiple axes as possible evidence of a damaged or uncontrolled object.
Then there’s the shape. Long and narrow, with an estimated aspect ratio unlike anything we’ve seen in nature, ʻOumuamua’s shape is most common compared to that of Rama, the massive cylindrical spacecraft from Arthur C. Clarke’s science fiction classic Rendezvous with Rama. In Clarke’s novel, the object is an alien starship silently spinning through the solar system—eerily similar, some say, to the real-life mystery of ʻOumuamua.
Whether natural or engineered, ʻOumuamua remains an enigma. But as technology improves and more interstellar objects are cataloged, we’ll likely arrive at one of two conclusions. Either ʻOumuamua turns out to be a strange but ultimately natural phenomenon—an object type common across the galaxy that we simply hadn’t encountered before—or it stays unmatched, the only one of its kind. And if the latter proves true, then ʻOumuamua will be a lot more than just unusual.
