The gardening robot on Mars

On Mars, at the bottom of a crater covered in red dust, stood a small clear greenhouse. Inside lived a robot called Trowel. It had four wheels, two arms as thin as a heron's legs, and a single job: to grow the first plant on the planet before the astronauts arrived.

It wasn't easy. Martian soil contains salts that poison plants, so Trowel had spent weeks rinsing it, handful by handful, with water melted from the ice underground. Outside, the air was so thin and cold that nothing could grow in the open. Inside the greenhouse, though, it was mild and damp. Trowel had planted a radish seed, and now it waited.

It waited a whole sol, which is a Martian day, a little longer than a day on Earth. Then two. Then six. Every morning it tilted its camera over the pot and sent a message to Earth: "Sol 6. Nothing yet. Soil moist. Temperature fine." The replies took long minutes to arrive, because Earth is very far away. "Patience, Trowel. Seeds take their time."

On the seventh sol, the sky turned orange, then brown. A dust storm was coming. On Mars the air is too thin for the wind to knock over a greenhouse, but the dust settles on everything. It covered Trowel's solar panels, and its batteries began to drain. To save power it had to switch almost everything off, keeping only the little heater under the pot running. "I'll be back soon," it told the seed, even though seeds don't listen.

The storm lasted eleven sols. Trowel dozed in the red gloom, counting the hours. It wondered whether the seed had stayed warm enough, whether the water had frozen, whether all its work would end right there.

On the twelfth morning, the wind dropped. A pale ray of sunlight broke through the dust and touched the panels, and Trowel slowly came back to life. It rolled over to the pot, tilted its camera and went perfectly still. In the middle of the dark soil, two tiny green leaves, folded like hands, had just come up. Its message was a single line: "Sol 18. It's here." A long while later, the answer arrived from Earth, with dozens of exclamation marks.

That evening Trowel didn't go back to its charging station. It stayed by the pot while the sun went down. On Mars, sunsets are blue, and the bluish light slid across the two little leaves. Up in the sky, Phobos, the smaller of Mars's two moons, passed among the stars. Trowel dimmed its light as low as it would go, set the heater to gentle and kept watch over its plant until morning.