The solar system's first confirmed interstellar visitor
In October 2017, astronomers detected ʻOumuamua, a fast-moving object skimming through our solar system on an unbound hyperbolic path. Its extreme speed and trajectory confirmed it was the first visitor ever observed arriving from interstellar space. Highly elongated and up to ten times longer than it is wide, the rocky interloper showed non-gravitational acceleration as it left, yet completely lacked the telltale glowing dust or gas coma of an ordinary comet.
An Unexpected Sighting from Deep Space
On October 19, 2017, astronomer Robert Weryk was reviewing data collected by the Pan-STARRS telescope atop Haleakala in Hawaii when he spotted an unfamiliar, rapidly moving point of light. The object had already made its closest approach to the Sun weeks earlier, passing inside the orbit of Mercury on September 9 before swinging upward past Earth on its journey back out into the cosmos. As astronomers traced its trajectory across the sky, its orbital calculations revealed something extraordinary: its orbit was not an ellipse, like that of every known planet, asteroid, and comet bound to the Sun, but an extreme hyperbola with an eccentricity well above 1.2.
This unmatched eccentricity, combined with an incoming velocity of roughly 26 kilometers per second relative to the Sun, proved beyond doubt that the object had not originated within our solar system. It had plunged inward from the direction of the constellation Lyra, near the bright star Vega, completely unbound by solar gravity. Because of this historic first, the International Astronomical Union established an entirely new designation category for interstellar interlopers, labeling the body 1I/2017 U1. It was officially given the Hawaiian name ʻOumuamua, a name chosen to signify a scout or messenger sent from a distant past to reach out to us.
Astronomers around the globe scrambled to coordinate observations before the fading visitor sped too far away. Because it was moving at dozens of kilometers per second and dimming rapidly as it receded from Earth and the Sun, major ground- and space-based observatories had only a fleeting window of a few weeks to gather meaningful data. Every major facility that could point toward ʻOumuamua was enlisted to uncover the physical nature of our solar system's very first confirmed interstellar guest.