The oceans cover more than 70% of the planet's surface, yet a significant portion remains unexplored even in this modern day. This vast and uncharted frontier has always enticed explorers to venture into the depths in search of new discoveries, whether it's uncovering hidden ecosystems, unknown species, submerged geological formations, or, popularly, ship wreckages. 

The sinking of the Titanic, arguably the most famous ship wreckage in history, is a topic of debate and discussion even more than 100 years after it happened. What began as the maiden voyage for the seemingly "unsinkable" vessel in April 1912 turned into a tragic tale of demise amidst immovable icebergs. Even now, parts of the sunken ship can be found in Newfoundland, Canada, where it originally sank. Most of the wreckage is stuck 12,500 feet below sea level, with the ship's bow and stern scattered over 2,600 feet apart. 

A popular method of exploring underwater depths, especially ship wreckages like that of the Titanic, is by using underwater vehicles known as submersibles. Here is a quick breakdown of what submersibles are and what the recently popular Titan submersible is all about.

What is a submersible?

Similar to submarines, a submersible can descend below the water surface and navigate the depths. But unlike submarines, a submersible runs on limited power reserves, and is dependent on being launched and retrieved by a surface vessel. While submersibles vary in shape and size depending on their specific purposes, their general use involves underwater exploration.

Usually made of materials like titanium or steel that can withstand great pressures, submersibles are equipped with navigation systems and tools that allow the passengers to explore and collect data underwater. Aside from research and exploration, submersibles are also used for commercial purposes. For example, the manufacturer of Titan, OceanGate Expeditions, offer deep-sea adventures for about $250,000 per person (including training, gear and even meals inside the submersible). 

According to the US-based underwater exploration organisation NOAA, there are mainly three types of submersibles, namely human-occupied vehicles (HOVs), remotely operated vehicles (ROVs), and autonomous underwater vehicles (AUVs). Submersibles can be manned or unmanned depending on their types and purposes.

HOV-type submersibles are small vessels that carry 4-5 people to the depths for a small amount of time, allowing the passengers to explore and observe the underwater first-hand. This is the type the Titan falls under.

ROV-type submersibles are unmanned, robotic vessels that are remotely controlled by the ship they are tethered to. Such submersibles are used to collect samples using robotic arms and explore further than a human body can on the seafloor. 

The third type, AUVs, are also unmanned robots, but instead of being manually controlled, they are pre-programmed to roam the ocean depths without real-time control. While they operate on their own, these autonomous submersibles follow a pre-planned route that allows scientists to conduct research while the robotic vehicle collects necessary data.

What is the Titan?

The Titan submersible, as per its manufacturer OceanGate Expeditions, is a manned submersible that is designed to take five passengers to a depth of 4,000 meters underwater. The primary purpose of the Titan is to collect data for research and survey underwater sites for inspections, though OceanGate states the submersible can also be used for media production and underwater software testing. 

The Titan submersible has a dimension of 670 x 280 x 250 cm (22 x 9.2 x 8.3 feet) and is primarily made of carbon fibre and titanium. It can travel at a speed of 3 knots and has four Innerspace 1002 electric thrusters for propulsion. Because of its low-weight pressure vessel materials, the Titan is notably light. While many manned submersibles range from 13,000 to 25,000 kg, the Titan weighs 10,432 kg (23,000 pounds). 

What makes this submersible unique is its Real-Time Hull Health Monitoring (RTM) system, which enables it to analyse how the increasing underwater pressure affects the vessel. This system helps the surface vessel, which monitors the submersible, keep track of how safe the passengers are and send early warnings to return to the surface in case of emergencies.

No bigger than a standard minivan, the Titan has limited seating capacity, with passengers having to sit on the floor against curved walls with little to no headroom. Additionally, the submersible is blocked from the outside, so even on the surface, passengers will not be able to get out without assistance.

According to OceanGate, Titan is "the only manned submersible to employ an integrated real-time health monitoring system", and has previously conducted over 50 test drives. 

The story so far

Last week, on June 16, Friday, a manned submersible expedition was hosted by OceanGate Expeditions. Set off from St John's, Newfoundland, Canada, their objective was simple: to explore the underwater wreckage of the historic Titanic ship. Thusly, the aptly named submersible 'Titan' housed 5 individuals of fame and fortune in the journey of a lifetime. 

Around noon on June 18, Sunday, the submersible began its descent deep into the belly of the North Atlantic Ocean. The dive was planned to be no longer than two hours and cover 4,000 metres (13,123 feet) of underwater depth, however, after 1 hour and 45 minutes, communications between the submersible and the surface vessel were lost.

At the time of writing (over 4 days since the Titan's descent), the submersible still hasn't been found, and experts fear the worse - as the air inside the underwater vehicle is not meant to last over 96 hours.