Swimming to Europa

It's a hot late-spring Friday on a cactus-studded cattle ranch in Mexico, and nothing is happening. Nothing, in fact, has been happening for going on a week now, and it's starting to get tedious. Ordinarily, the group of scientists, engineers, and students who have gathered here might have enjoyed a respite from their otherwise crazy schedules. But they didn't come here to catch up on their reading, play the guitar, or take long, leisurely walks. They came here to work. Their goal is to field-test one of the most intelligent and agile underwater robots ever crafted, a possible predecessor of a machine that might someday swim the vast, ice-crusted ocean of Jupiter's mysterious moon Europa. Called DEPTHX, for DEep Phreatic THermal eXplorer, the 1.3-metric-ton machine can maneuver freely, draw detailed, three-dimensional maps of its watery surroundings, and collect solid and liquid biological samples as it senses changing conditions in its environment. Most important, it does all that without any guidance from human operators. Such autonomy would be essential if the robot ever does swim on Europa--which may be warm enough, thanks to geothermal activity, to have given rise to some sort of life. Human control of a robot sub that far away isn't an option: radio waves don't effectively penetrate water. Even if they did, a round-trip radio signal would take 2 hours or more, making remote control unlikely. But today, on this sweltering retreat near the Gulf Coast of Mexico, with cicadas buzzing and a hazy sun beating down, Europa seems a long way off.