It looks like a heap of rubbish, feels like flaky pastry and has been linked to aliens. For decades, scientists have puzzled over the complex collection of cogs, wheels and dials seen as the most sophisticated object from antiquity, writes Helena Smith. But 102 years after the discovery of the calcium-encrusted bronze mechanism on the ocean floor, hidden inscriptions show that it is the world's oldest computer, used to map the motions of the sun, moon and planets.

'We're very close to unlocking the secrets,' says Xenophon Moussas,an astrophysicist with a Anglo-Greek team researching the device. 'It's like a puzzle concerning astronomical and mathematical knowledge.'

Known as the Antikythera mechanism and made before the birth of Christ, the instrument was found by sponge divers amid the wreckage of a cargo ship that sunk off the tiny island of Antikythera in 80BC. To date, no other appears to have survived.

'Bronze objects like these would have been recycled, but being in deep water it was out of reach of the scrap-man and we had the luck to discover it,' said Michael Wright, a former curator at London's Science Museum. He said the apparatus was the best proof yet of how technologically advanced the ancients were. 'The skill with which it was made shows a level of instrument-making not surpassed until the Renaissance. It really is the first hard evidence of their interest in mechanical gadgets, ability to make them and the preparedness of somebody to pay for them.'

For years scholars had surmised that the object was an astronomical showpiece, navigational instrument or rich man's toy. The Roman Cicero described the device as being for 'after-dinner entertainment'.

But many experts say it could change how the history of science is written. 'In many ways, it was the first analogue computer,' said Professor Theodosios Tassios of the National Technical University of Athens. 'It will change the way we look at the ancients' technological achievements.'