NASA’s 2001 Mars Odyssey spacecraft turned its multipurpose camera homeward last week and took its first picture — a shot of a faint crescent Earth — as the spacecraft heads off toward its destination, the planet Mars. The image was taken as part of the calibration process for the thermal emission imaging system, the camera system that is one of three science instrument packages on the spacecraft. The imaging system will study the Martian surface in both visible and infrared light and will help determine what minerals are present. It also will map landscapes on Mars at resolutions comparable to that of NASA’s Landsat Earth observing satellite.