Oumuamua

Oumuamua is the first known interstellar object to pass through the Solar System

Oumuamua is the first known interstellar object to pass through the Solar System. Formally designated 1I/2017 U1, it was discovered by Robert Weryk using the Pan-STARRS telescope on 19 October 2017, 40 days after it passed its closest point to the Sun. When first seen, it was about 33,000,000 km (21,000,000 mi; 0.22 AU) from Earth (about 85 times as far away as the Moon), and already heading away from the Sun. Initially assumed to be a comet, it was reclassified as an asteroid a week later, then the first of a new class of interstellar objects.

ʻOumuamua is a small object, estimated to be about 230 by 35 meters (800 ft × 100 ft) in size. It has a relatively high density, comparable to metal-rich rock, and a dark and very red color, similar to objects in the outer Solar System. ʻOumuamua is tumbling rather than smoothly rotating, and it is moving so fast through space relative to the Sun that there is no chance it originated in the Solar System. It also means that ʻOumuamua can not be captured into a solar orbit, so it will eventually leave the Solar System and resume traveling in interstellar space. ʻOumuamua's system of origin and the amount of time it has been traveling among the stars are unknown.