Descent to Challenger Deep

It's the deepest part of the earth, pitch black and with pressure so enormous that it is equivalent to one person carrying 50 jumbo jets.

Yet scientists say the Mariana Trench, 11 kilometres deep in the Pacific Ocean, is teeming with life.

The trench, named after a 17th-century Spanish queen, could soon be the site of one of the most dangerous but greatest explorations in our history.

Sir Richard Branson and US entrepreneur Chris Welsh say that designer Graham Hawkes has created a one-man winged submarine that is so advanced in its engineering it can not only dive into one of the least explored places on our planet, but also "fly" around it.

But the risks are immense. Just a simple leak in the submarine could cause it to implode and be crushed like a paper cup.

So few other submersibles can descend to such a depth that "rescue is impossible", Mr Welsh said.

"It's like being on the dark side of the moon."

And way down there are creatures we don't yet know about.

Sir Richard and Mr Welsh hope to explore five trenches in all, the deepest points of the world's oceans. The Mariana Trench is the deepest.

So how will they overcome the dangers and what will they see as they head towards the ocean floor?

Engineering challenges

The last human explorers of the Mariana Trench in the Pacific Ocean were Don Walsh and Jacques Piccard, in the US Navy's Bathyscaphe Trieste, in January 1960. (Unmanned descents were undertaken by the Japanese submersible Kaiko in 1996 and the Woods Hole Oceanographic Institution's Nereus in 2009.)

But the Trieste, which was 18.4 metres long and had a sphere with steel walls 12.7 centimetres thick to withstand pressure of up to 1250 kilograms per square centimetre, was bulky compared with the Virgin Oceanic's DeepFlight Challenger submarine.

The Challenger is designed by Mr Hawkes, who also created the Deep Rover submersibles used by film director James Cameron in his IMAX movie Aliens of the Deep, and is just 5.4 metres long, 3.8 metres wide and 1.7 metres high.

The pressure at the bottom of the Mariana Trench is up to 1000 times normal atmospheric pressure at sea level.

To combat this, the Challenger - named after the deepest point of the Mariana Trench, the Challenger Deep - is made from 3630 kilograms of carbon fibre and titanium, its creator said.

It has a quartz viewing dome that not only gives a 180-degree view, but will also be able to withstand almost 6 million kilograms of pressure, the weight of three space shuttles. This durability is enough for the craft to withstand the pressures of the Challenger Deep, Mr Hawkes said.

The submarine is pressurised at one atmosphere - the same pressure a person experiences at sea level - so the solo pilot does not need to wear a special suit.

And while the Trieste could only plunge straight down into the Trench before heading back up again, the Challenger is expected to dive downwards at 107 metres a minute, reaching the bottom of the Trench before "flying" around unaided for up to 10 kilometres in 24 hours.

Mr Hawkes said he designed the sub to use the downward lift of its wings, instead of ballast, to propel it through and down into the ocean. It takes off like a plane, by speeding on the water surface at about two knots before it dives nose down.

In the dark depths of the trenches, the submersible uses low wattage LED lights and laser "feeler" beams instead of wide arc lights so that it causes as little disruption to marine life as possible, Mr Hawkes said.

Creatures of the deep

What Sir Richard and Mr Welsh see when they make their descent is expected to be spectacular.

Scientists previously believed the bottom of the oceans were barren deserts.

But following studies by scientists Howie Sanders and Robert Hessler, the first of which was published in 1967, it became known that the deep sea was rich with life, just like other shallower waters.

"There'll be a lot of new species that have never been seen or discovered before, I have no doubts about that," University of Western Sydney marine biologist Dr Sebastian Holmes said.

There willl be varieties of strange looking crabs, starfish and fish, which can cope with the immense pressure because they breathe liquid, rather than air.

And there could be ancient life forms that moved to the depths because there is less competition for food.

In this "sub-optimal habitat", the giant squid, which has been found off the coast of Australia, the giant isopod and the coelacanth could survive, Dr Holmes said.  The coelacanth existed almost 400 million years ago according to fossil records and was believed to have gone extinct 80 million years ago until it was found off the South African coast in 1938.

'Dog-eat-dog world'

Food in these depths is scarce as most that descends would be eaten by bacteria before reaching the bottom.

So staying alive would depend on eating your neighbours or living near a hydrothermal vent, where chemosynthesis - the conversion of chemicals into carbohydrates and energy, rather than photosynthesis - takes place, Dr Holmes said.

"There is no primary production. It is a bit of a dog-eat-dog world," he added.

Bioluminescent fish, such as the anglerfish, would use their light to attract prey to them.

The five trenches Sir Richard and Mr Welsh hope to explore are the: Mariana Trench (about 11 kilometres deep).Diamantina Trench in the Indian Ocean (about eight kilometres deep).South Sandwich Trench in the Southern Ocean (about 7.2 kilometres deep).Puerto Rico Trench in the Atlantic (about 8.4 kilometres deep).Molloy Deep Trench in the Arctic Ocean (about 5.6 kilometres deep).

Besides being some of the deepest parts of the oceans, the trenches are "geological factories", formed by great rifts in the earth that rend apart or push together, said marine geologist and deep-sea mapper Rob Beaman at James Cook University in Queensland.

"Geologically, it's fascinating. It's either where new crust is born or dies, is either subsumed by the overriding plate or is created," Dr Beaman said.

"These are where the dynamic earth is really taking place."

The two pilots would descend down vast cliffs of rocks, feeding data to Google Earth and scientists at research labs in the United States.

If the dives are successful, the public would, via the free Google program, get to explore on their computers a part of the earth rarely seen before.

In contrast, when the Trieste descended into the Challenger Deep in 1960, it had no cameras on board, and Mr Piccard and Captain Walsh could only share their personal experiences of seeing a flatfish and a shrimp-like creature on the sea bed.

"From a scientific point of view, this is akin to discovering the Amazon for the first time," Sir Richard said. "The amount that they're going to discover down there is incalculable."

The Challenger submarine will be pressure tested before its first dive, with Mr Welsh at the helm, into the Mariana Trench later this year.

Sir Richard will then pilot the second dive into the Puerto Rico Trench. The five expeditions are expected to take place over two years.

The billionaire, who in 2009 unveiled the world's first space tourism rocket, wants to break up to 30 Guinness world records with his latest adventure. But he is not expecting to break the bank, saying that the whole project would cost less than $US10 million ($9.6 million).

Ever the businessman, he hopes that, one day, the Oceanic project could take passengers into the deep ocean.

As he noted in a blog on his Virgin website, there was a "whole new world" waiting to be explored.

"A world full of undiscovered species and for those who dream, a world where Spanish galleons have lain unplundered for centuries!"

Deeper than deep1020 metres - deepest operating military submarine.3000 metres - maximum depth for the sperm whale.3810 metres - the Titanic's resting place.5606 metres - deepest point in the Arctic Ocean, the Molloy Deep.5762 metres - deepest shipwreck found.6000 metres - test depth of the Russian Mir submersible.6500 metres - maximum depth of the Japanese Shinkai submersible.7235 metres - deepest point in the Southern Ocean, the South Sandwich Trench.8047 metres - deepest point in the Indian Ocean, the Diamantina Trench.8380 metres - deepest point in the Atlantic Ocean, the Puerto Rico Trench.8848 metres - height of Mount Everest.11034 metres - deepest point on earth the Mariana Trench.

The oceans' five layersThe epipelagic zone - from the surface to 200 metres.The mesopelagic zone - from 200 to 1000 metres.The bathypelagic zone - from 1000 to 4000 metres.The abyssopelagic zone - from 4000 to 6000 metres.The hadopelagic (hadal) zone - deeper than 6000 metres.

Further reading:The Census of Marine Life, a 10-year project involving scientists from more than 80 countries.The Mariana Trench in the Pacific Ocean.The deep ocean.The Bathyscaphe Trieste.

(Data from the US's National Oceanic and Atmospheric Administration, UK's National History Museum)

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