What is Oumuamua? 6 facts about the first mysterious visitor to enter our solar system

Oumuamua was first detected on October 19, 2017 by the University of Hawaii’s Pan-STARRS1 telescope. Officially, it has been named 1I/2017 U1 by the International Astronomical Union. However, it was the first confirmed interstellar object observed passing through our solar system. Its Hawaiian name, ‘Oumuamua, means 'a messenger from afar arriving first.' It was briefly classified as an asteroid until new signs and findings established that it was accelerating slightly, a sign it behaves more like a comet.

Estimates have suggested that the object is up to 400 metres long and is highly elongated, possibly ten times longer than it is wide. Its reddish colour shows resemblance with that of outer solar system objects. Observations have indicated that it rotates every 7.3 hours, with brightness changes by a factor of 10. This is far more than typical solar system asteroids or comets. It was discovered at a blistering speed of 196,000 miles per hour ( which means 87.3 kilometers per second).

Oumuamua appeared to be rocky or metallic and it showed no visible signs of gas or dust, which are typical characteristics in comets. Its dry, inert surface and the lack of cometary tail puzzled astronomers. The reddish surface is thought to result from prolonged exposure to cosmic rays over millions of years during its journey through interstellar space.

After passing closest to the Sun on 9 September 2017, Oumuamua accelerated in a way not fully explained by gravitational forces alone. The non-gravitational acceleration of this body, led to initial confusion and debate over whether it was a comet, asteroid, or something else entirely. 'Oumuamua entered our solar system from the rough direction of the constellation Lyra, but it’s impossible to tell where it originally came from.

Some researchers, including Harvard astronomer Avi Loeb, proposed that Oumuamua could quite possibly be a piece of alien technology or a light sail. However, the prevailing scientific view is that it is rather, a natural object, possibly a dark comet or a hydrogen ice body. Its behaviour, however, remains inconsistent with known solar system bodies.

Oumuamua, which is travelling at 87.3 kilometres per second (196,000 miles per hour), entered from above the plane of the planets and is now on an outbound path toward the constellation Pegasus. It had passed Mars's orbit by November 2017 and there are expectations that it might exit the solar system after 2038.

Oumuamua is very likely to have travelled for hundreds of millions of years through the Milky Way before it reached our solar system. Astronomers have estimated that similar interstellar objects may pass through once a year, but most go undetected.