Bill Stone is not an astronaut—he is the world's most famous caver. Leading large international teams and backed by sponsors like the National Geographic Society, he has mounted more than 50 major expeditions to measure the depth of the most hostile reaches of inner space. Spending weeks underground, his crews have traveled deep inside our planet to the remotest locations touched by humans. Nobody is better at what he does, but this gives him limited satisfaction. He is consumed by ideas for how humanity could explore space and wants to personally establish a privately funded base on Jupiter(木星). It is, he thinks, nothing less than destiny. A reasonable observer might choose other words: obsession, fantasy. Bill possesses neither great wealth nor extensive political connections. He is an engineer and runs Stone Aerospace, a company so small that when FedEx rings, he usually signs for the package himself. So to hear Bill talk—'It's not a big leap for me to go to Jupiter. For Bill, caves are a proving ground. The experience gained there will help people explore outer space. But now, after spending nearly three decades on the margins of the space industry, Bill is closer than he's ever been to proving that caves are the best earthly training ground for exploring space. Backed by a $5-million fund from NASA, he is developing a robot called DepthX that may turn out to be the most advanced autonomous underwater vehicle (AUV) ever. NASA hopes to someday use a robot like Bill Stone's DepthX to explore Europa, a frozen moon of Jupiter and one of the most probably places in our solar system to support life. Like its inventor, DepthX is a caver, most capable of searching harsh environments. Its theoretical mission, though, is bold even by Bill's standards: a hunt for extraterrestrial(地球外的) life on Europa. Innovator Bill Stone plans to drop one of the world's most advanced underwater robots, DepthX, into the deepest hole on Earth. If all goes well, this thing just might help get him to Europa DepthX's first major field trial will take place this month in Mexico's Zacatén Cenote, the world's deepest hole. For Bill's future space ambitions to have any chance, he needs to impress the new generation of wealthy space-loving investors. To do that, he needs to ace(取得好成绩) this first trial and, at 54 years old, he needs to do it fast. As one of his oldest friends puts it, 'Time is running out for Bill.' What have Bill Stone and his teams accomplished?