'Oumuamua: a visitor from deep space

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On 18th October 2017 a strange object was seen by astronomers that could only have come from outside the Solar System. It was given the name `Oumuamua, which means “scout” in the Hawaiian language. The cigar-shaped object, no more than a kilometre in length and about 140 metres in diameter, was clearly moving at high speed and it soon passed out of the range of Earth-based telescopes. Efforts were then made to find it by using the Spitzer Space Telescope (which operates in the infrared frequency range) but these were unsuccessful. The Hubble Space Telescope was also used in the search, and had more success, but not a lot more. However, there were various factors that limited the observations that could be made. One was `Oumuamua`s small size, another was its dimness. When a comet traverses the inner Solar System it emits a trail of gases and particles that make it relatively easy to see, but this was not the case with `Oumuamua, which emitted almost no carbon dioxide or monoxide. Another reason for the lack of direct observation was that `Oumuamua was not moving at the speed that had been predicted for it. This might have been due to ice on its surface turning into gas as it passed the Sun and speeding it up. When the Spitzer telescope was pointed at its expected position it had already moved beyond it. Another oddity about `Oumuamua it that it is tumbling end over end but still moving at great speed. This speed is such that there is no possibility of any probe being able to launch and move towards it, because any such probe would never be able to catch up. As to what `Oumuamua is and where it came from, these are questions that have yet to be answered. One suggestion is that it could be part of an alien spaceship that broke up in interstellar space, possibly millions of years ago. It has been speculated that `Oumuamua is not alone in visiting the Solar System from somewhere else. Some of these objects might well be captured by the Sun’s gravity and end up in orbit as asteroids or comets. Several asteroids have been identified that are on eccentric or tilted orbits that suggest an origin outside the Solar System. These will clearly be much easier to investigate than a fleeting visitor like `Oumuamua. (The picture is an artist’s impression of `Oumuamua)