Pictured here under the warm red glow of a water-cooled, LED-based lighting system, "space lettuce" is growing in an aeroponic greenhouse module designed for use on the moon or Mars. The plants are suspended from soil-free trays and their dangling roots sprayed with nutrients for 20 seconds every 2 minutes. LEDs are needed because the sunlight on Mars is too weak to fuel photosynthesis. "On the moon we would most likely use artificial light too," says DLR engineer Daniel Schubert. "It makes more sense that way because the lunar night is about 14 Earth days long." The plant's healthy root system is visible both in Schubert's hand and, below, in normal light. For colonists, growing plants will be a key home comfort, but it's a two-way deal: astronauts will have to nourish their salad crops with their own waste fluids. Each greenhouse module will scavenge chemicals from astronaut urine to produce fertiliser. The system will be tested in the hostile wastes of Antarctica in 2016.