Virgin billionaire Richard Branson is joining a new mission to solve one of the most captivating mysteries of the ocean -- what lies at the bottom of the Great Blue Hole in Belize?

The Great Blue Hole in Belize is the largest sinkhole in the world -- a giant cavern measuring 300 meters (984 feet) across and around 125 meters deep.

In 1971, underwater explorer Jacques Cousteau put the Blue Hole on the map when he first explored its depths.

Nearly half a century later, despite becoming a scuba hotspot, the Blue Hole's exact features remain mostly unknown. But Cousteau's grandson, Fabien Cousteau, is on the case, CNN says.

He'll be joinging Branson -- who runs Ocean Unite, a leadership initiative that aims to help protect the ocean -- and a team of scientists, explorers and filmmakers from the Aquatica Foundation.

They're planning to take submersibles including a manned Aquatica Stingray 500 to the bottom of the hole to chart what lies deep down below.

The Blue Hole Belize 2018 Expedition, as it's been titled, will be broadcast live on the Discovery Channel on Sunday December 2, 2018.

Located roughly 40 miles off the Belize coast, the Blue Hole is thought to have once been a giant cave on dry land, thousands of years ago.

As the ocean rose again, the cave flooded. It's now part of the wider Belize Barrier Reef Reserve System, which is a UNESCO World Heritage Site.

The Blue Hole has never been fully mapped or plotted -- the idea is this new expedition might answer the question of what lies at the bottom of this enigmatic cavern.