Oumuamua

Oumuamua, officially designated 1I/2017 U1 and commonly named Oumuamua, was the first known object detected passing through the Solar System that originated outside it. It was discovered on October 19, 2017, by astronomer Robert Weryk using the Pan-STARRS1 telescope at the Haleakalā Observatory in Hawaii. Its interstellar origin was inferred from its hyperbolic trajectory and a velocity at infinity well above solar-system escape speed.

Trajectory and speed details indicate that Oumuamua approached the Sun on a hyperbolic path and passed closest to the Sun on October 19, 2017 at a distance of about 0.255 astronomical units. After its perihelion, it accelerated away from the Sun and rapidly faded from observation as it moved out of the inner Solar System. Its inbound and outbound speeds suggested it was traveling through interstellar space at a high velocity relative to the Sun.

Physical characteristics and observations: Oumuamua exhibited no detectable cometary coma or tail during its detection, which was unusual for an object passing near the Sun. Photometric data showed significant brightness variation as it rotated, implying a highly elongated shape. Size estimates varied widely, with most results suggesting a length on the order of tens to hundreds of meters and a substantial length-to-width ratio, though precise dimensions remain uncertain.

Non-gravitational acceleration and interpretation: Analyses of its trajectory indicated a small deviation from gravitationally determined motion, leading to discussion of possible outgassing as a driver, or alternative explanations such as radiation pressure. The absence of a visible coma made the cause controversial, and subsequent interpretations remained a topic of scientific debate.

Discovery and naming significance: The name Oumuamua means “scout” or “messenger” in Hawaiian, reflecting its passage through the Solar System. Oumuamua is regarded as the first confirmed interstellar object, highlighting that others may traverse the Solar System and prompting expectations for future interstellar visitors, such as 2I/Borisov, discovered in 2019.