Wailing Asteroid — Murray Leinster

The public abruptly ceased to be interested in news of the signals. Rather, it suddenly wanted to stop thinking about them. The public was scared. Throughout all human history, the most horrifying of all ideas has been the idea of something which was as intelligent as a man, but wasn't human.

The first sounds came at midnight, a plaintive keening from an unknown voice in the vastness of uncharted space. Within hours the whole world had heard the strange, unearthly music--and the panic had begun.

Were the sounds a plea for help? From whom? From where? Or were they a command too terrible to think about? No one knew: And in billions of earth-bound minds the horror grew...

For how could man, who had not yet claimed the moon, defy a challenge from the stars?

And hours later, to the ears of a helpless world, the second message came. . .

And Earth's days were numbered.