Research into plant growth on missions to Mars. Fresh food, such as vegetables, would provide essential vitamins and nutrients that would enable sustainable deep space pioneering. The lettuce plants in this image were grown in an experiment comparing (left to right) potting soil, Mars regolith simulant with added nutrients, and simulant without nutrients. Terrestrial soil is full of organic matter, while the 'soil' on Mars, called regolith, consists of crushed volcanic rock containing toxic chemicals that would inhibit plant growth.