An Unsent Letter

The signal arrived at 03:17 station time, when Dr Anjali Rao was the only person awake on Europa and, by her own estimate, the loneliest person in the solar system.

It came up through forty kilometres of ice as a series of low clicks, spaced with a regularity that made the hair on her arms stand up. Click, pause, click click, pause. Then silence. Then the whole sequence again, exactly the same.

She checked the hydrophone. She checked the cables, the power, the temperature of the drill head resting in the dark water at the bottom of the borehole. Everything was normal. Everything was working. That was the problem.

“Station,” she said quietly, “play back the last ten minutes of hydrophone data.”

The computer obliged. In the small, humming control room, surrounded by screens and cold coffee cups, she listened to the ocean of another world talk to itself, and then, unmistakably, stop and wait.

Anjali had spent her whole career listening to whales. She knew what a question sounded like.

She reached for the transmit switch, hesitated, and took her hand away. On the monitor above her, the clicks began again, patient as a knock on a door.