Titanic sub latest news: What we know about search for the OceanGate submersible

A massive effort to find a submersible exploring the wreck of the Titanic in the North Atlantic has entered a critical stage. The vessel went missing deep under the ocean on Sunday with five people on board.

Researchers aboard the Polar Prince - its mothership on the surface - lost contact with the crew shortly after the Titan began its dive. There is limited oxygen on board, and it was estimated that supplies would run out by around 10:00 GMT (06:00 EDT) on Thursday.

Undersea noises have been detected in the search area, but it is not known where they are coming from or what they mean.

US, Canadian and French agencies are working together to locate the submersible, and the tour firm OceanGate says it is exploring all options to get it back safety. Here is what we know so far.

A Canadian search plane picked up underwater noises on Tuesday and Wednesday. Deep-sea experts say it is hard to determine what these noises might be without seeing the data.

But there is hope that they could be the short, sharp, relatively high frequency noises, made at regular intervals from within the vessel by hitting a hard object against the end of the sub.

The US Coast Guard says it does not know what the noises are at this point. It says the US navy is analysing the data, but so far it remains inconclusive.

The US Coast Guard has sent ROVs - remotely operated vehicles - to search under the surface in the area where sounds have been detected. But so far, they have yielded negative results, it said.

More ROVs are being deployed with extra-depth capability. You can read more about the equipment being used in our visual guide.

Authorities say the search area has been expanded to an area approximately twice the size of the US state of Connecticut, and a sub-surface search area of around 2.5 miles (4km) deep.

Planes are continuing to search from the air, in case Titan has returned to the ocean's surface but somehow lost communications.

One of the vessels on its way to help search efforts is French ship L'Atalante which has a robot that can reach the seabed 3,800m (12,500ft) down, and has the capacity to lift the Titan sub to the surface.

In total, there were currently five surface vessels involved in the search, with a further five heading to the area.

If the sub is still intact, the main worry is the prospect of oxygen running out.

US Rear Adm John Mauger from the US Coast Guard has said the sub is believed to have an emergency life-support system onboard to provide oxygen. The crew originally had 96 hours worth of oxygen.

Although the timeline from the Coast Guard suggests the oxygen will run out by Thursday morning, it is difficult to estimate exactly when it might happen - and one of the factors determining it is the rate of consumption for each individual, and that is not known.

Prof Alistair Greig, a submarine expert from University College London, says one of the big problems is that rescuers do not know whether to look on the surface or the seabed - it is very unlikely to be in between.

He's worked through a couple of scenarios. One is that it released a "drop weight" after an emergency, in order to bring it to the surface.

"If there was a power failure and/or communication failure, this might have happened, and the submersible would then be bobbing about on the surface waiting to be found," he said.

Another possibility is that the hull was compromised resulting in a leak. "Then the prognosis is not good," he says.

The wreck of the Titanic sits 3,800m (12,500ft) beneath the surface of the Atlantic. If the submersible has gone down to the seabed and can't get back up under its own power, the options are very limited.

We know there are very few vessels that can get that deep, and certainly not divers. The vehicles designed for navy submarine rescues can't get anywhere near as deep as would be needed.

According to OceanGate, the company that owns it, Titan is one of only five manned submersibles in the world capable of reaching the depth required.

The French-operated ship heading to the scene has an ROV that can operate at the depth of the Titanic wreckage.

The five people on board are:

You can read more about them all here.

OceanGate Expeditions charges guests $250,000 (£195,270) for a place on its eight-day expedition to see the wreck of the Titanic.

The site is about 600km (370 miles) off the coast of Canada's Newfoundland, and lies in two parts, with the bow and the stern separated by about 800m (2,600ft). A huge debris field surrounds the broken vessel.

A full dive to the wreck, including the descent and ascent, reportedly takes eight hours and each trip is meant to include a scientific objective, including studying the wreck's decay.

The inaugural dive took place in 2021, according to the company's website.

The Titan is extremely small and narrow, measuring just 670 cm x 280 cm x 250 cm (22ft x 9.2ft x 8.3ft) and can carry a crew of just five people - a pilot and four passengers, who have to sit on the floor and have limited room to move around.

Aside from taking divers to the wreck of the Titanic, it's used for site survey and inspection, research and data collection, film and media production, and deep sea testing of hardware and software.

According to the company, the Titan is "outfitted with state-of-the-art lighting and sonar navigation systems plus internally and externally mounted 4K video and photographic equipment".

The BBC's US partner CBS sent one of its reporters on a voyage with the same company last year to see the wreck of the Titanic.

Stockton Rush then gave him a tour of the submersible, where he revealed the vessel only has one button and is run using a video game controller.

It is not unusual for off-the-shelf game controllers to be used in real-life vehicles. However, the Washington Post reports that the one seen in the CBS report appeared to be an old model.

The Polar Prince first arrived near the Titanic wreck on Sunday morning and the Titan was launched at 08:00 local time - it was expected to resurface at 15:00. Contact was lost one hour and 45 minutes into its descent, at about 09:45.

The Coast Guard said they were notified of the problem at about 17:45 - eight hours later. The agency's command centre in Boston then began coordinating search efforts.

The Titanic wreck site is approximately 600km (370 miles) off the coast of Newfoundland.

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