The robotic deep-sea submersible Nereus was destroyed while diving over six miles beneath the surface in the Kermadec Trench off the New Zealand coast, researchers reported this week. Parts of the unmanned vehicle are thought to have imploded under pressure as great as 16,000 pounds per square inch during the dive, which was planned to help study deep-sea ecosystems. The submersible was one of only four vehicles to have explored the Challenger Deep in the Mariana Trench, the deepest part of the oceans. Timothy Shank, a marine biologist at Woods Hole Oceanographic Institute and chief scientist on the HADES mission, describes Nereus and what its loss might mean for deep-sea research.