The Impossible Answer

At 14:07, the communications screen at Arcadia Base lit up with a message from Earth: “AUTHORISED. OPEN AIRLOCK B.” Rocío Vidal, the engineer on duty, let out the breath she had been holding and leapt to her feet. “At last,” she said. “I’m going to open it.”

Outside, the dust storm had turned the afternoon into a reddish night. Somewhere in that darkness, the rover was heading back to the base with Dr Marta Ibarra, Kai’s mother, on board, and only one hour of reserve oxygen. It could come in through either of the base’s two airlocks: A, on the north side, or B, on the south side, the closer one to its route.

But airlock B had been showing a possible-leak warning all morning. The base rules were clear: with a leak warning, that airlock must not be opened without permission from mission control, back on Earth. That was why, at 14:02, Rocío had sent the question: “Leak warning on airlock B. Can we open it to let the rover in?”

Kai, who was fourteen and had been glued to the screen all afternoon, looked at the whiteboard on the wall. There, as every day, someone had written in marker the figure that mattered most for talking to home: “Signal delay today: 12 minutes.” That was how long a message took to travel, at the speed of light, from Mars to Earth. And the same to come back.

Kai looked at the clock. He looked at the whiteboard again. Then he planted himself in front of the door to the south corridor.

“Rocío, wait. That message isn’t the answer to your question.” In the corner of the screen, the rover’s signal was blinking: it would reach the base in ten minutes. By the north side, in fifteen.