They’re sending a greenhouse on wheels to Mars. Genetically modified plants will be grown in martian soil inside the lander. The plants were modified to bioluminesce under certain conditions, and will basically serve as one of the lander’s instruments. The mission doesn’t even launch until 2007, though, so we’ll have to wait a while before the plants escape the lander, take over the entire planet, and turn it into a psychedelic glowing orb in our night sky. Which won’t actually happen, of course. It would be too cool.