Beneath the surface of the Pacific Ocean to the southeast of Japan, there is a very deep, crescent-shaped trench called the “Mariana Trench." Near the southern tip of the crescent, there is a small slot-shaped area called the “Challenger Deep."

With a measured depth of approximately 36,000 feet below sea level, a journey to the bottom of the Challenger Deep is nearly seven miles, making it the deepest known place on Earth. To give you an idea of just how deep the Mariana Trench is, if Mt. Everest were placed in the deepest part, there would still be over a mile of water above its peak!

The Challenger Deep is named after a British Royal Navy ship called the HMS Challenger. The Challenger was the first ship to measure the depths of what is now known as the Challenger Deep.

The trench was measured by “sounding," which involves dropping a very long line with a weight at the end into a body of water. Improvements and advancements in technology have allowed modern scientists and researchers to use sonar to study ocean depths.

Only four descents into the Challenger Deep have ever been achieved. The first was in 1960 by a vessel called the Trieste. The Trieste was a special kind of ship called a “bathyscaphe," invented by Jacques and Auguste Piccard. The name “bathyscaphe" is taken from the Greek words for “deep" and “ship."

The Trieste's journey into the trench took almost five hours, while its return to the surface took three hours and 15 minutes. It remained on the ocean floor for only 20 minutes, due to a crack in a window caused by the extreme pressure.

The second descent into the Challenger Deep was made in 1995 by an unmanned deep-sea robotic probe named Kaiko. Kaiko measured the Challenger Deep at 35,696 feet. Kaiko also collected samples from the bottom of the deep.

The third descent into the Challenger Deep took place in 2009, when the U.S. Navy sent the Nereus on an exploration. The Nereus is a hybrid remotely-operated vehicle, also known as an HROV.

The Nereus spent more than 10 hours at the bottom of the Challenger Deep, sending live video and data back to a ship at the surface. Using a robotic arm, the Nereus also collected geological and biological samples from the ocean floor.

The most recentnt descent into the Challenger Deep happened in 2012 by solo-diver James Cameron in the DEEPSEA CHALLENGER. He collected film footage, along with photographs and samples of water and deep sea organisms. The project is now in its second phase—scientific analysis of the expedition's findings.