In October 2017, a telescope in Maui spotted something unusual. It was a tiny, moving object that didn’t seem to belong to our solar system. This object, later named ‘Oumuamua, was the first confirmed interstellar visitor. It had zipped by the Sun just weeks earlier, and by the time it was discovered, it was already heading back into deep space.
The Discovery
Robert Weryk, using the Pan-STARRS1 telescope run by the University of Hawaii and NASA, found ‘Oumuamua on October 19. The name means “a messenger from afar arriving first” in Hawaiian. Scientists had a limited time, about two weeks, to study it before it faded from sight.
They figured out a few key details: it was moving at incredible speeds—about 26 kilometers per second. Its orbit was steeply hyperbolic, meaning it wasn’t gravitationally tied to our Sun. The object also had a unique brightness that fluctuated dramatically, suggesting it was elongated, though its exact shape remains a mystery.
The Puzzle of Its Path
In June 2018, researchers led by Marco Micheli noted a perplexing detail: as ‘Oumuamua traveled away from the Sun, it exhibited a slight push that couldn’t solely be explained by gravity. For comets, this push is usually caused by gas escaping as they near the Sun. However, ‘Oumuamua showed no signs of a tail or debris—no dust or gas was detected.
This lack of visible outgassing left scientists puzzled. What could cause the extra push? One theory was that it contained some hidden material that wasn’t detected. Recent studies, including work by Jennifer Bergner and Darryl Seligman, suggested that molecular hydrogen trapped in ice might explain the mystery. As the object warmed, this hydrogen could be released, creating a thrust without leaving behind a visible trail.
Alternative Theories
Other possibilities have emerged too. Avi Loeb, an astronomer from Harvard, proposed a more radical idea: what if ‘Oumuamua was artificial? He suggested it could be a sail-like object pushed by sunlight. Most researchers, however, lean toward natural explanations, as there is no direct evidence to support the notion of an artificial origin.
Keeping the Mystery Alive
The challenge lies in the lack of data. ‘Oumuamua was fleeting—spotted on its way out and never revisited. No spacecraft have examined it, leaving scientists with only limited observations.
Since the discovery of ‘Oumuamua, more interstellar objects have been found. For instance, 2I/Borisov was observed in 2019, displaying typical comet behavior with a visible tail. In 2025, 3I/ATLAS was identified as another cometary object. The Vera C. Rubin Observatory is expected to discover even more, which will provide valuable context and possibly help to confirm or refute existing theories about ‘Oumuamua.
The future holds promise. As more interstellar visitors come to light, scientists hope to better understand the nature of these objects. Each new discovery adds piece by piece to the puzzle that ‘Oumuamua has left us with. Until then, it remains a fascinating and unresolved enigma in the universe.
