Today in the history of astronomy, we meet our first interstellar visitor.
‘Oumuamua, the first known interstellar visitor, appears to be releasing gas and dust in this artist’s concept. Credit: ESA/Hubble, NASA, ESO, M. Kornmesser
- In 2017, the Pan-STARRS1 telescope identified an astronomical object, later named 1I/2017 U1 or ‘Oumuamua, that 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 about four months of observations due to ‘Oumuamua’s rapid movement away from the Sun and subsequent loss of detection capability.
- Following the discovery of ‘Oumuamua, comets 2I/Borisov in 2019 and 3I/ATLAS in July 2025 were identified as additional interstellar objects.
Around the year 1837, a strange object passed by an invisible cosmic mile marker: 1,000 astronomical units from the Sun. (An astronomical unit, or AU, is the average Earth-Sun distance.) For more than a century, it continued unnoticed toward our star. Finally, on October 19, 2017, humans sighted the visitor.
That night, a faint, thin line appeared in a 45-second-long image taken by the University of Hawaii’s Pan-STARRS1 telescope on Maui. The next morning, postdoctoral researcher Robert Weyrick observed the streak and compared it to an image taken the day before. The object was also there. It was moving continuously across the sky and covering about 6.2° every day.
By October 22, two things were clear: The object was in a hyperbolic orbit, meaning it comes close to our Sun only once and then moves away, never to return. And, based on its orbit, it did not originate in our solar system at all, but 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” in Hawaiian. After its discovery, ‘Oumuamua was moving so rapidly that astronomers had only four months to observe it; After that, the object moved far away from the Sun, losing our ability to track it. But in 2019, we will 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.
