His depth on arrival: 35,756 feet (10,898 meters)—a figure unattainable anywhere else in the ocean.
Reaching bottom after a 2-hour-and-36-minute descent, the National Geographic explorer and filmmaker typed out welcome words for the cheering support crew waiting at the surface: "All systems OK."
Folded into a sub cockpit as cramped as any Apollo capsule, the National Geographic explorer and filmmaker is now investigating a seascape more alien to humans than the moon. Cameron is only the third person to reach this Pacific Ocean valley southwest of Guam (map)—and the only one to do so solo.
Hovering in what he's called a vertical torpedo, Cameron is likely collecting data, specimens, and imagery unthinkable in 1960, when the only other explorers to reach Challenger Deep returned after seeing little more than the silt stirred up by their bathyscaphe.
After as long as six hours in the trench, Cameron—best known for creating fictional worlds on film (Avatar, Titanic, The Abyss)—is to jettison steel weights attached to the sub and shoot back to the surface. (See pictures of Cameron's sub.)
Meanwhile, the expedition's scientific support team awaits his return aboard the research ships Mermaid Sapphire and Barakuda, 7 miles (11 kilometers) up. (Video: how sound revealed that Challenger Deep is the deepest spot in the ocean.)
"We're now a band of brothers and sisters that have been through this for a while," marine biologist Doug Bartlett told National Geographic News from the ship before the dive.