The deepest depths of the sea are in the shape of a crescent moon Mariana Trench, located in the western Pacific Ocean. But what is the deepest point of the Mariana Trench?
The Mariana Trench is about 1,580 miles (2,550 kilometers) long and lies east of the Mariana Islands, which give the trench its name, according to the University of Washington (opens in new tab). The deepest point in the Mariana Trench is a valley called the Challenger Deep, located at the southern end of the Mariana Trench, according to the National Oceanic and Atmospheric Administration (opens in new tab) (NOAA).
According to NOAA, Challenger Deep extends about 35,876 feet (10,935 meters) below the surface. This makes it about 7,000 feet (2,100 meters) deeper than Everest it is tall noted NOAA (opens in new tab).
The NOAA estimate comes from a 2021 study in the journal Deep Sea Research Part I: Oceanographic Research Papers (opens in new tab), based on data from a 2020 voyage. However, there are many other estimates of the depths of the Challenger Deep. The first manned mission there, in 1960, returned about 35,797 feet (10,911 meters), according to Guinness World Record (opens in new tab). Since then, recent estimates include; 36,069 feet (opens in new tab) (10,994 m) and 36,036 ft (10,984 m (opens in new tab)).
Why is it so difficult to estimate the depth of the Challenger Deep? “Basically, it’s hard because it’s so deep,” said Cmdr. Sam Greenaway of NOAA and lead author of the 2021 study told Live Science.
Related: What are the deepest points in Earth’s oceans?
To measure ocean depths using modern instruments, scientists basically have two options: sonar mounted on a ship on the surface of the ocean, or a pressure sensor on the bottom that can help measure how much water is above it, Greenaway said.
Sonar beams from multibeam echoes “can produce complete coverage of the seabed,” said Greenaway, the marine operations chief for NOAA’s new shipbuilding group. “As good as they are, shipboard systems are very far from the seabed, which limits both the horizontal and vertical accuracy of the measurement.”
For example, with the Challenger Deep, “it takes sound about 14 seconds to get down to the bottom and back,” and water salinity, temperature and pressure can affect the speed and path the sound takes, said Greenaway. As a result, the vertical accuracy of an echo measurement is about 80 feet (25 meters), he noted.
With a pressure sensor, making a pressure gauge that is accurate enough at such high pressures is quite difficult, Greenaway said. On the floor of Challenger Deep, the pressure is more than 1,000 times greater than standard atmospheric pressure at sea level, Guinness World Records noted.
“After that, we have to correct for the density of the water above the sensor, gravity pulling that water down, atmospheric pressure and tides,” Greenaway noted. “Deploying a pressure sensor in the right place is also a trick.”
To make their measurements, Greenaway and his colleagues dropped a pressure sensor on the sea floor to serve as a reference point for the echo measurements. “The pressure sensor uncertainty dominated our overall uncertainty, but instrument makers are making great progress in improving these sensors, so I expect that this component of uncertainty can improve significantly in the future,” he said.
The surfaces of both Mars and the Moon are mapped with greater resolution and precision than the ocean floor, Greenaway said in a Reddit post (opens in new tab). “I’ve spent most of my career working with various aspects of seafloor mapping,” he told Live Science. “I think it’s a surprise to a lot of people how much of this mapping work remains to be done.”
In practical terms, “the difference between Challenger Deep being 10,935 meters deep, as we determined, or 10,984 meters, as a recent mapping campaign estimated, doesn’t matter that much,” Greenaway said. “However, the idea that we need to go out and measure the depth of the world’s oceans is really important.” For example, such research can help with precise positioning of underwater vehicles, as well as pressure sensors to help monitor water level fluctuations due to climate change, he said.
Depth is also important to deep-sea explorers. On March 26, 2012, cinematographer James Cameron dove 35,787 feet (10,908 m) in the Deepsea Challenger submarine in the ocean trench, setting the record for the deepest solo dive. In 2019, explorer and entrepreneur Victor Vescovo made the deepest dive on record, at 35,853 feet (10,927 m) in the Pacific Ocean. Vescovo worked with deep-sea experts, including Captain Don Walsh, a US Navy oceanographer known for diving with Swiss oceanographer and engineer Jacques Piccard at Challenger Deep on January 23, 1960. They became the first people to reach the deepest part of the ocean, at about 35,814 feet (10,916 m).