Key Takeaways:
- In 2017, the Pan-STARRS1 Telescope identified a celestial object, later named 1I/2017 U1 or ‘Oumuamua, which had entered our solar system around 1837.
- Subsequent observations confirmed ‘Oumuamua's hyperbolic trajectory, establishing its origin from outside our solar system and marking it as the first identified interstellar visitor.
- Astronomers were limited to approximately four months of observation due to ‘Oumuamua's rapid departure from the Sun and subsequent fading from detectability.
- The discovery of ‘Oumuamua was followed by the identification of Comet 2I/Borisov in 2019 and 3I/ATLAS in July 2025 as additional interstellar objects.
Sometime around the year 1837, a strange object passed an invisible cosmic mile marker: 1,000 astronomical units from the Sun. (One astronomical unit, or AU, is the average Earth-Sun distance.) For more than a century, it continued undetected toward our star. Finally, on Oct. 19, 2017, humans noticed the visitor.
That night, a faint, thin streak appeared in a 45-second-long image snapped by the University of Hawai’i’s Pan-STARRS1 Telescope on Maui. The next morning, postdoctoral researcher Robert Weryk spotted the streak and compared it to an image taken the day before. The object was there, too. It was moving steadily across the sky, covering about 6.2° each day.
By Oct. 22, two things were clear: The object was on a hyperbolic orbit, meaning it comes close to our Sun only once and then shoots away again, never to return. And, based on its orbit, it did not originate in our solar system at all, but instead came from another star system. It was our first known interstellar visitor. Officially named 1I/2017 U1, the object is also known as ‘Oumuamua, which means “a messenger from afar arriving first” in Hawaiian. Following its discovery, ‘Oumuamua was moving so fast that astronomers had a scant four months to observe it; after that, the object had retreated too far from the Sun, fading past our ability to track it. But in 2019, we’d meet our second interstellar visitor, Comet 2I/Borisov, and in July of 2025, the third known object from outside our solar system, 3I/ATLAS, was spotted.
