What is "challenger deep"

n. A point in the Mariana Trench, known as the deepest point in the world's oceans.

The Challenger Deep is the deepest known point in the Earth's seabed hydrosphere, with a depth of by direct measurement from submersibles, and slightly more by sonar bathymetry. It is in the Pacific Ocean, at the southern end of the Mariana Trench near the Mariana Islands group. The Challenger Deep is a relatively small slot-shaped depression in the bottom of a considerably larger crescent-shaped oceanic trench, which itself is an unusually deep feature in the ocean floor. Its bottom is about long and wide, with gently sloping sides. The closest land to the Challenger Deep is Fais Island (one of the outer islands of Yap), southwest, and Guam, to the northeast. It is located in the ocean territory of the Federated States of Micronesia, from its border with ocean territory associated with Guam.

The depression is named after the British Royal Navy survey ship HMS Challenger, whose expedition of 1872–1876 made the first recordings of its depth. According to the August 2011 version of the GEBCO Gazetteer of Undersea Feature Names, the location and depth of the Challenger Deep are and ±.

June 2009 sonar mapping of the Challenger Deep by the Simrad EM120 (sonar multibeam bathymetry system for 300–11,000 m deep water mapping) aboard the RV Kilo Moana indicated a depth of . The sonar system uses phase and amplitude bottom detection, with a precision of 0.2% to 0.5% of water depth; this is an error of about at this depth. Further soundings made by the US Center for Coastal & Ocean Mapping in October 2010 are in agreement with this figure, preliminarily placing the deepest part of the Challenger Deep at , with an estimated vertical uncertainty of ±. A 2014 study concludes that with the best of 2010 multibeam echosounder technologies a depth uncertainty of ± (95% confidence level) on 9 degrees of freedom and a positional uncertainty of ± (2drms) remain and the location of the deepest depth recorded in the 2010 mapping is at .

Only four descents have ever been achieved. The first descent by any vehicle was by the manned bathyscaphe Trieste in 1960. This was followed by the unmanned ROVs Kaikō in 1995 and Nereus in 2009. In March 2012 a manned solo descent was made by the deep-submergence vehicle Deepsea Challenger. These expeditions measured very similar depths of .