OK, so he's not an autonomous bot, but we simply have to give more props to the Deep Submergence Vehicle known as Alvin. The oldest and most venerable vehicle of its kind, Alvin has completed over 4,400 dives over the course of its momentous, 46-year career.
In the late 1970s, Alvin and his passengers discovered the first known hydrothermal vents, or "black smokers" as they are sometimes called. Initially, scientists thought that no species, let alone a bustling community, could survive the scorching temperatures and crushing pressures of these sites, most of which are located about 7,000 feet below the ocean surface in areas of seafloor spreading.
To their great surprise, researchers found out that not only did the magma-heated, mineral-rich water spurts support life, they nursed entire ecosystems.