The terrain of the seabed, the depth and the pressure are so great that the search and rescue mission for the submersible carrying five passengers to visit the Titanic wreck is extremely difficult.

OceanGate Expeditions’ Titan submersible. Photo: CTV

OceanGate Expeditions’ Titan submersible. Photo: CTV

Rescue workers searching for the submersible that disappeared while visiting the Titanic wreck not only have to race against time due to the decreasing oxygen level on the ship, but also have to cope with a harsh environment that is more like space than Earth, according to NBC. “The environment down there is pitch black and freezing cold. The seabed is muddy and bumpy. You can’t see your hand in front of your face,” said historian and Titanic expert Tim Maltin. “It’s really a bit like an astronaut flying into space.”

The 22-foot-long (6.7-meter) deep-sea submersible operated by OceanGate Expeditions disappeared on June 18 with five passengers on board, prompting a search and rescue mission in the northern Atlantic Ocean, about 400 miles (644 kilometers) off Newfoundland, Canada. But unlike space, human presence in the deep sea is rare and search and rescue technology is limited.

Coast Guard officials estimated that by the afternoon of March 20, the remaining oxygen on the missing submersible would last only about 40 hours. The US Coast Guard is coordinating with the Navy and Canadian partners to conduct the search. Several civilian vessels have also sailed to the area where the submersible went missing to help. The French government has announced that it will send ships equipped with deep-sea submersibles to assist in the search and rescue effort.

The amount of oxygen on board is the most stressful part of the search, but it’s not the only challenge, according to Jamie Pringle, a professor of geoscience at Keele University in the UK. Navigating at such extreme depths is difficult because the seafloor is much rougher than on land. The Titanic, which sank more than a century ago, lies at a depth of about 12,000 feet. The ocean floor is not flat, but has many hills and deep canyons, Pringle said. If the submersible gets stuck on the seafloor, locating the ship would be really difficult.

Even searching around the Titanic wreckage is difficult because the area is so vast. The Coast Guard said on March 20 that the search is focused on an area of ​​the North Pacific Ocean about the size of Connecticut. There are very few vessels and equipment that can work at such great depths. The vehicles need to be designed to withstand the extreme depths and pressures.

At the depths of the Titanic wreck, the pressure is about 400 times greater than at sea level, according to the Woods Hole Oceanographic Institution. Some military nuclear submarines can dive as deep as 1,500 feet, but most modern submarines operate in much shallower waters. Few vehicles can go thousands of feet, said Henry Hargrove, a senior analyst who served in the U.S. Navy for 11 years.

Rescue workers have deployed several C-130 aircraft to conduct aerial surveys of the area, and sonar buoys that can pick up signals as deep as 12,000 feet are also being used to search underwater. However, sonar systems typically need to scan at greater depths to detect objects as small as a submersible inside the Titanic wreck site, according to Pringle.

Pringle said it was difficult to speculate about what happened to the missing submersible. Authorities also don’t know if rescue vessels can be deployed to such great depths in time, or how the process of recovering the stranded submersible will proceed. Submersibles like OceanGate Expeditions’ Titan typically don’t have a mechanism in their hull that another vessel can hook onto and tow.