Oumuamua: alien starship or just another piece of rock?

The National -- As Star Wars fans try to contain their excitement over this week’s premiere of The Last Jedi, astronomers are agog at a real-life space drama playing out in our own solar system.

The Earth has just had its first known encounter with an object from another star - and there’s already talk it may have been an alien spacecraft.

The drama began in mid-October, when astronomers in Hawaii detected an incredibly faint object about 33 million km from Earth. At first it seemed like just another chunk of debris left over from the creation of the planets. But as more data came in, astronomers realised the object was like nothing else they had ever seen.

Plotting out its path, they found it had swooped in from the abyss of space in early September, shooting past the sun at an astonishing 315,000 kph and was already heading back out.

Calculations revealed it was on a so-called hyperbolic trajectory, unlike the elliptical paths of ordinary comets and asteroids.

That means the sun’s gravity has never been able to hold on to the object, which must have started its journey in another star system.

This makes 1I/‘Oumuamua – as the object is now officially called – the first known visitor from interstellar space.

But astronomers got another surprise when they turned some of the world’s largest telescopes onto the object for a closer look.

They were expecting it to be some kind of comet, one of the myriad piles of dust and ice known to orbit other stars. But ‘Oumuamua appears to be something different. Despite shooting past the sun closer than the planet Mercury, it showed no sign of melting in the heat, and lacked the bright tail of a comet.

Instead, analysis of the sunlight bounced off its surface reveal ‘Oumuamua to be deep red in colour, consistent with long exposure to cosmic rays in deep space, and sometimes seen on asteroids.

But the mystery deepened again when data revealed that ‘Oumuamua is shaped like a long cylinder, around 200 to 400m long and around one-tenth as wide. No known comet or asteroid has such a bizarre shape.

By the end of this month, ‘Oumuamua will be beyond the reach even of the world’s most powerful telescopes, and its true nature will remain forever unknown.