Based on a 29-day observation arc, ʻOumuamua's orbital eccentricity is 1.20, the highest of any object yet observed in the Solar System. The previous record holder was C/1980 E1 with an outbound-orbit eccentricity of 1.057. The high eccentricity of ʻOumuamua both inbound and outbound indicates that it has never been gravitationally bound to the Solar System and is presumably an interstellar object due to its high incoming velocity. It has an inclination of 123° with respect to the ecliptic, and had a speed of 26.32 km/s (58,900 mph) relative to the sun when in interstellar space, which peaked at 87.71 km/s at perihelion
This is the first known example of an interstellar object, appearing to come from roughly the direction of the star Vega in the constellation Lyra, with a hyperbolic excess velocity of 26 km/s with respect to the Sun. This direction is close to the Solar apex, the most likely direction for approaches from objects outside the Solar System. But it is unknown how long the object has been drifting among the stars in the galactic disc. The Solar System is likely the first star system that ʻOumuamua has closely encountered since being ejected from its birth star system potentially several billion years ago.
On October 26, 2017, two precovery observations from the Catalina Sky Survey were found dated October 14 and October 17. A two-week observation arc has verified the strongly hyperbolic nature of this object. Observations and conclusions on the composition, shape, behavior and origin compiled from the Very Large Telescope in
Assuming it is a rock with an albedo of 10%, it would be approximately 160 meters (500 ft) in diameter. Spectra recorded by the 4.2-meter William Herschel Telescope on October 25 showed that the object was featureless, colored red like Kuiper belt objects. Spectra from the Hale Telescope showed a less red color resembling comet nuclei or Trojans. Its spectrum is similar to that of D-type or P-type asteroids.
1I/ʻOumuamua has a rotation period of 8.1 hours, with a lightcurve amplitude of 1.8 mag. This indicates that it is a highly elongated object with an axis ratio of at least 5.3:1, comparable to the most elongated Solar System objects. According to astronomer David Jewitt, the object is physically unremarkable except for its highly elongated shape. Assuming an albedo of 0.1 (typical for D-type asteroids), 1I/ʻOumuamua has dimensions of approximately 180 × 30 × 30 meters. Bannister, et al. have suggested that it could also be a contact binary.
Extrapolating the orbit backwards, the asteroid is calculated to have gone through perihelion on September 9, 2017 and to have passed approximately 0.1616 AU (24,180,000 km; 15,020,000 ) from Earth on October 14, 2017. The object is small and faint, and by the end of October had already faded to apparent magnitude ~23.
It has been speculated that the object may have been ejected from a stellar system in the Carina-Columba association some 45 million years ago. The Carina-Columba stellar association is now very far in the sky from the constellation Lyra, the direction from which the object came. About 1.3 million years ago the object may have passed the nearby star TYC4742-1027-1 within a distance of 0.16 parsecs (0.52 light-years), but its velocity is too high to have originated from this star as it probably just passed through the Oort cloud of that system at a speed of 103 km/s.
One hundred years ago, the object was 7002561000000000000♠561±0.6 AU (84 billion km) from the Sun and traveling at 26 km/s with respect to the Sun. The object continued to speed up until it went through perihelion, where it peaked at 87.7 km/s. By the discovery date it had slowed down to 46 km/s and will continue to slow down until it reaches a speed of 26 km/s relative to the Sun. This interstellar speed is within ~5 km/s of other stars within the Sun's stellar neighborhood, which also indicates an interstellar origin. The object will ultimately head away from the Sun at an angle of 66° from the direction it came from. As it leaves the Solar System, it will be around R.A. 23h51m and declination +24°45', in Pegasus.