Taking a page out of a science fiction story, researchers have successfully flown the first environmentally powered robotic vehicle through the ocean. The new robotic “glider” harvests heat energy from the ocean to propel itself across thousands of kilometers of water. Unlike motorized, propeller-driven vehicles, gliders propel themselves through the ocean by changing their buoyancy to dive and surface. Wings generate lift, while a vertical tail fin and rudder allow the vehicles to be steered horizontally. Gliding underwater vehicles trace a saw-tooth profile through the ocean’s layers, surfacing periodically to fix their positions via the Global Positioning System and to communicate via Iridium satellite to a shore lab.