A submarine mission called "Five Deeps" is going to explore the bottom of each of the world's oceans.

First up: the depths of the Atlantic. The mission will launch from the coast of Puerto Rico in December.

We may not know where the deepest point in the ocean really is. This team wants to find out.

Imagine exploring a place so far from humanity that any message you send takes seven seconds to be heard.

That's arguably more remote than the moon — radio waves sent back-and-forth during the Apollo missions took just 2.5 to 2.7 seconds to transmit.

But this location isn't in space; it's at the bottom of the sea.

In December, explorer and investor Victor Vescovo, along with scientist Alan Jamieson from Newcastle University, are embarking on a groundbreaking mission more than 6.5 miles under the waves. The two are heading out in a new $48 million dollar submarine system to better map the bottom of the world's five oceans.

They're calling the mission, which will be the first time people travel to the bottom of each of the world's seas, "Five Deeps."

"Our depth of ignorance about the oceans is quite dramatic," Vescovo said as he introduced the mission to an audience in New York. "Four of the oceans have never even had a human being go to their bottom. In fact, we don't even know with great certainty where the bottom of the four are."

First up on the five-dive trip will be the Puerto Rico Trench, the deepest point in the Atlantic Ocean. It's a spot no human has ever explored, and it's so deep that any communications from the submarine will take seven seconds to travel back up.

The Triton 36000 deep-sea submarine

Jamieson's research often sends cameras and sample boxes to the sea floor, but that's not the same as going there.

"The geomorphology of these trenches is really like nothing you can see on land," he said. "This is where the planet is pushing the sea floor back into the Earth's mantle."

In the Puerto Rico Trench, more than 5 miles under the surface of the water, the pressure is immense: over 800 times what it is at sea level.

To better handle that high-pressure environment, the hull of the Triton 36000 submarine that Vescovo and Jamieson will travel in will morph and change shape on their three-hour journey to the Atlantic Ocean's floor.

"The acrylic moves a quarter of an inch deeper towards Victor, as he gets down to those depths," Triton engineer John Ramsey explained. "The whole thing is shifting and changing shape."

The submarine will probably scare off most of the animals that live in the pitch-black part of the ocean more than 3,280 feet below the surface. But the vessel should be much better at mapping the ocean floor than satellites, thanks to its 3-D sonar system. The sub might collect some critters that don't scare easily in biological sample boxes and sediment cores that the team will pick up.

"Then we can start to look at what it is that's driving these ecosystems," Jamieson said. "By looking at a warm trench versus a cold trench, shallow trenches versus big ones, you start to knock out the variables and see the commonalities."

After the Puerto Rican dive, the vessel will spend the next seven months, until August 2019, zig-zagging its way to the four other deepest places in the planet's oceans, including one spot that we think is the deepest of them all.

The five dives will take place between December 2018 and August 2019. Five Deeps Expedition

The deepest 45% of the ocean has gone 'largely ignored,' and we don't know where the bottom of the ocean really is

While hundreds of people have ventured into space, and a dozen have landed on the moon, only three have touched down on the deepest known place on the sea floor, the Challenger Deep.

That's a spot at the bottom of the Mariana Trench in the Pacific Ocean, almost 7 miles underwater — a location farther down from sea level than Mount Everest is up.

Film director James Cameron went there in 2012, and explorers Jacques Piccard and Don Walsh did it more than 50 years earlier in 1960. But that's it.

Jamieson said the deepest 45% of the ocean has been essentially ignored by explorers. The South Sandwich Trench in the Southern Ocean hasn't even been named yet, so the Five Deeps crew is looking forward to claiming naming rights there.

It's possible, however, that the Challenger Deep isn't really the deepest place in the ocean after all.

Jamieson said much of today's sea floor mapping is based off of very "dodgy" information. And a lot of data is inferred from satellite pictures.

"The deeper you go, the more your error is," he said. "I've certainly been to places in the Indian Ocean, just the last year, the depth was over 1,000 meters shallower than it was supposed to be."

Jamieson and Vescovo think it's possible that they'll discover a place deeper than the Challenger Deep.

"The Tonga Trench, off the Island of Tonga, is less than 100 meters shallower," Vescovo said. "If we go to the Tonga Trench, and we find a canyon, rest assured I'm going to be diving to that canyon to get that depth... to hopefully find a new discovery of the deepest ocean in the world."

Vescovo will perform each of the trailblazing submarine dives alone for the first plunge, before potentially inviting Jamieson or others on board his two-seater sub for a ride down.

This refitted Navy ship will carry the $48 million sub around the world. Five Deeps Expedition

There's no rescue crew

The trickiest dives on the mission will also be the coldest.

The team plans to travel to the 18,600-foot-deep Molloy Deep in the Arctic for its final mission in August. The area is not nearly as deep as the other trenches they'll explore, but it's another place where no human's ever been.

With climate change warming up the ice that normally sits atop the water, the seas are a bit rougher too, so the crew expects that Arctic dive to be their toughest challenge of all.

When you're 5 to 7 miles underwater, and all alone, anything that goes wrong could prove deadly. The engineers who've designed this submarine admit that it's going to a lung-crushing depth.

"There's very little chance of getting rescued when you're down 11 kilometers (6.8 miles)," Ramsey said, quickly adding, "well, there's no chance."

For that reason, the vessel doesn't move very fast on these missions, typically no quicker than about 3.5 mph. And it's got some other safety features designed to keep it from getting stuck below.

"We've made anything that the sub could potentially get entangled in ejectable," Ramsey said, explaining that the thrusters, batteries, and manipulator arm of the submarine can all be released and fall off the machine. "What you're left with, once everything's been ejected, is quite a different-looking vehicle."

Vescovo, who's a pilot and former Navy reserve intelligence officer, says safety is also the reason he asked that the submarine be made of titanium, even though it means he only has three palm-sized porthole-style windows to peek through.

"I trust titanium, not glass," he said.

Vescovo added that he's relieved to know the oxygen tanks inside will still be accessible, even if the electronics fail. "We have multiple avenues of getting that oxygen out of the bottles to keep us alive," he said.

His first dive, which should last less than six hours, will take place during the first week in December.