Something of the sort had been expected for a hundred years, and there had been many false alarms. Yet when it finally happened, mankind was taken by surprise.
The radio signal from the direction of Alpha Centauri was so powerful that it was first detected as interference on normal commercial circuits. This was highly embarrassing to all the radio astronomers who, for so many decades, had been seeking intelligent messages from space – especially as they had long ago dismissed the triple system of Alpha, Beta and Proxima Centauri from all serious consideration.
At once, every radio telescope that could scan the southern hemisphere was focused upon Centaurus. Within hours, a still more sensational discovery was made. The signal was not coming from the Centaurus system at all – but from a point half a degree away. And it was moving.
That was the first hint of the truth. When it was confirmed, all the normal business of mankind came to a halt.
The power of the signal was no longer surprising; its source was already well inside the solar system, and moving sunward at six hundred kilometres a second. The long-awaited, long-feared visitors from space had arrived at last.
Yet for thirty days the intruder did nothing, as it fell past the outer planets, broadcasting an unvarying series of pulses that merely announced “Here I am!”. It made no attempt to answer the signals beamed at it, nor did it make any adjustments to its natural, comet-like orbit. Unless it had slowed down from some much higher speed, its voyage from Centaurus must have lasted two thousand years. Some found this reassuring, since it suggested that the visitor was a robot space-probe; others were disappointed, feeling that the absence of real, live extra-terrestrials would be an anti-climax.
The whole spectrum of possibilities was argued, ad nauseam, in all the media of communications, all the parliaments of man.
Every plot that had ever been used in science fiction, from the arrival of benevolent gods to an invasion of blood-sucking vampires, was disinterred and solemnly analysed. Lloyds of London collected substantial premiums from people insuring against every possible future – including some in which there would have been very little chance of collecting a penny.
Then, as the alien passed the orbit of Jupiter, man's instruments began to learn something about it. The first discovery created a short-lived panic; the object was five hundred kilometres in diameter – the size of a small moon. Perhaps, after all, it was a mobile world, carrying an invading army.
This fear vanished when more precise observations showed that the solid body of the intruder was only a few metres across. The five-hundred-kilometre halo around it was something very familiar – a flimsy, slowly revolving parabolic reflector, the exact equivalent of the astronomers' orbiting radio telescopes. Presumably this was the antenna through which the visitor kept in touch with its distant base. And through which, even now, it was doubtless beaming back its discoveries, as it scanned the solar system and eavesdropped upon all the radio, TV and data broadcasts of mankind.
Then came yet another surprise. That asteroid-sized antenna was not pointed in the direction of Alpha Centauri, but towards a totally different part of the sky. It began to look as if the Centauri system was merely the vehicle's last port of call, not its origin.
The astronomers were still brooding over this when they had a remarkable stroke of luck. A solar weather probe on routine patrol beyond Mars became suddenly dumb, then recovered its radio voice a minute later. When the records were examined, it was found that the instruments had been momentarily paralysed by intense radiation. The probe had cut right across the visitor's beam – and it was then a simple matter to calculate precisely where it was aimed.
There was nothing in that direction for fifty-two light-years, except a very faint – and presumably very old – red dwarf star, one of those abstemious little suns that would still be shining peacefully billions of years after the galaxy's splendid giants had burned themselves out. No radio telescope had ever examined it closely; now all those that could be spared from the approaching visitor were focused upon its suspected origin.
And there it was, beaming a sharply-tuned signal in the one centimetre band. The makers were still in contact with the vehicle they had launched, thousands of years ago; but the messages it must be receiving now were from only half a century in the past.
Then, as it came within the orbit of Mars, the visitor showed its first awareness of mankind, in the most dramatic and unmistakable way that could be imagined. It started transmitting standard 3075-line television pictures, interleaved with video text in fluent though stilted English and Mandarin. The first cosmic conversation had begun – and not, as had always been imagined, with a delay of decades, but only of minutes.