The deepest place on Earth is the next holy grail for the deep-sea exploration community. Only two humans have ever been down to the Mariana Trench in the western Pacific Ocean off the coast of Guam, and that was well over 50 years ago.

Now a recent University of New Hampshire survey of the area shows that Challenger Deep, the deepest point on the planet, is actually even deeper than was previously thought. Earlier measurements had marked Challenger Deep between 10,902 and 10,916 meters (about 35,767 to 35,813 feet). The new depth reading shows Challenger Deep to be closer to 10,994 meters (36,069 feet), plus or minus 40 meters (131 feet).

Four bridge-like features spanning the massive trench were also discovered, each rising more than 8,000 feet above the seafloor. These bridges were likely formed from seamounts compacted when the older Pacific crust got pushed below the Philippine tectonic plate.

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UNH marine geologist James Gardner told the Daily Mail that there might even be life on these bridges that’s adapted to the harsh, cold, and high-pressure environment.

The UNH team used multibeam echo sounders mounted underneath a hydrographic U.S. Navy ship, the USNS Sumner. The instruments send out sound waves and record depth based on the echo bounced off the seafloor, the university reported. The mission was led by Gardner and affiliate ocean engineering professor Andrew Armstrong at UNH’s Center for Coastal and Ocean Mapping/UNH-NOAA Joint Hydrographic Center.

In a process oceanographers call “mowing the lawn,” the ship made overlapping passes over the trench while the instruments sent out their dolphin-like signals to map the seafloor. The topographic perspective built with the multibeam echo sounders provided a 3-D model of the trench’s terrain at one pixel for every 100 meters — a far higher resolution than systems used in the past.

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The UNH team used thousands of readings to correct for the way the water column can alter echo sounding signals.

Meanwhile, several teams worldwide are still developing underwater vessels in a bid to return to the depths of the Mariana Trench. Now the pressure is even greater to reach this goal.

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Image: A new map of the Mariana Trench with an arrow showing the deepest echo sounding there in meters. Credit: University of New Hampshire Center for Coastal and Ocean Mapping Joint Hydrographic Center.