Mystery deepens: cigar-shaped rock which zipped through solar system is cloaked in organic material

A cigar-shaped rock zooming through our Solar System – the first object from a foreign star system ever spotted in our midst – is cloaked in a coat of organic material, astronomers said on Monday.

Dubbed Oumuamua, Hawaiian for “messenger” or “scout”, the object was first viewed by telescopes in October. Given its weird trajectory, surprised scientists immediately concluded it was from beyond our own planetary system.

Astronomers had long assumed that interstellar objects from other star systems would be mainly small, comet-like, ice-rich bodies.

Yet Oumuamua did not eject a comet-like “tail” of molten dust and ice when it swung by the Sun in September, implying it had no surface ice and might in fact belong to the family of asteroids composed mainly of metals and rock.

On Monday, scientists said Oumuamua’s true nature remained a mystery, and a cometary character could not be ruled out.

Spectroscopic readings revealed it sported a half-metre coat of organic-rich material which could have protected a water-ice interior from being vaporised by the Sun.

“An internal icy composition cannot … be ruled out,” a team wrote in the journal Nature Astronomy.

Oumuamua is about 400 metres long, and thin – only about 40 metres wide, a never-before-seen shape for such a body.