Marianas trench, Marianas trough, or Marianas deep (mârˌēănˈəz) [key], elongated depression on the Pacific Ocean floor, 210 mi (338 km) SW of Guam. It is the deepest known depression on the earth's surface, having been measured by various means at 35,760–36,089 ft (10,900–11,000 m) below sea level at Challenger Deep. The Trieste, a U.S. navy bathyscape crewed by Swiss oceanographyer Jacques Piccard and U.S. Navy Lieutenant Donald Walsh, reached its bottom in 1960. A 1995 Japanese probe made what is probably the most accurate measurement of its depth (35,798.6 ft/10,911.5 m), and in 2009 a U.S. robotic vessel explored the seafloor of Challenger Deep. In 2012 James Cameron became the third person to descend to the Deep, in the submersible Deepsea Challenger.