It appeared in orbit around Earth one day, twenty-six kilometers long, a complex structure of stacked slate shards. It was so big anyone could go out and see it, just by looking up, even during the day. At night it blotted out a mass of stars.

It was impossible to hide. Statements were issued, agitated press conferences with shouted questions, sleep-deprived spokespeople and scientists standing in front of improbably large clusters of microphones.

Yes, they’d seen it decelerate and make orbit.

No, it didn’t appear dangerous.

Yes, they were watching it.

No, they hadn’t had any luck contacting it.

Yes, it was obviously artificial and therefore proof that we were no longer alone in the universe.

Beyond the TV screens, street parties sprang up. Some turned into protests. In many cities, protests soured into riots.

Six days after it arrived, it changed shape and moved in to a complex harmonic orbit shuttling between the Earth and the moon.

Three days later it left - or at least, part of it did.

At the last press conference, they announced the visitor vessel had sped off at almost half of lightspeed. It left behind a nine-kilometer wide sphere, coated in diamond, shuttling between the Earth and the Moon in that same complex harmonic orbit.

That was the kicker.

Someone worked out the orbital mechanics. That orbit is stable for the next three years, and then the sphere will crash right into Italy.

So, you could say we’ve been given a countdown.