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

A massive search and rescue effort is under way in the North Atlantic after a submersible exploring the wreck of the Titanic went missing on Sunday.

The research vessel Polar Prince lost contact with the crew of the Titan sub an hour and 45 minutes into its dive. Search authorities estimate that the sub has fewer than 30 hours of oxygen left - meaning supplies are set to run out by around 10:00 GMT (06:00 EDT) on Thursday.

A Canadian aircraft has now detected "underwater noises" in the search area.

Tour firm OceanGate says it is exploring all options to get the crew back safely, and government agencies have joined the rescue operation. Here is what we know so far.

In the early hours of Wednesday, the US Coast Guard said Canada's P-3 search plane had detected "underwater noises in the search area".

"As a result, ROV (remotely operated vehicle) operations were relocated in an attempt to explore the origin of the noises. Those ROV searches have yielded negative results but continue," the coast guard tweeted.

Earlier, two US media outlets had reported a leaked US Department of Homeland Security memo which said "banging sounds" had been detected by another Canadian aircraft, a P-8, equipped with underwater detection capabilities.

As of Tuesday afternoon local time, US and Canadian forces and private vessels had searched a 7,600 square mile area, roughly the size of the US state of Connecticut, according to US Coast Guard Capt Jamie Frederick.

Capt Frederick said the search was "very complex" and a "unique operation" made more difficult by the remoteness of the area.

A commercial pipe-laying ship has also arrived in the area to help, said David Mearns, a marine scientist and expedition leader who has been following the operation.

"We're just hoping that it has the capabilities to reach those kind of depths - 3,800 metres - to search for the submersible and have the ability to recover it," he told the BBC. "There is some hope that that could happen."

The Polar Prince first arrived near the Titanic wreck on Sunday morning and the Titan was scheduled to start its dive early that day at 04:00 local time. The Titan lost contact with the surface one hour and 45 minutes into its descent, at about 09:45 local time.

There was a delay between when the the Polar Prince lost contact with the submersible and when the US Coast Guard was notified.

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 Titan submersible is thought to be approximately 900 miles (1450km) east and 400 miles (643km) south of St. Johns, Newfoundland.

The US Coast Guard's Rear Admiral John Mauger said on Monday that the search has two aspects: a surface search in case the Titan has returned to the ocean's surface but somehow lost communications, and an underwater sonar search.

Two C-130 Hercules aircraft from the US Coast Guard, a Canadian C-130 and the Canadian coast guard vessel Kopit Hopson are assisting with the search - as well as sonar buoys that detect underwater sounds. Horizon Maritime, which co-owns the Polar Prince, is also helping and has sent a second vessel, the Horizon Arctic, to the site.

Mr Mauger said additional expertise would be needed to rescue the vessel if it was found underwater, and that the Coast Guard has reached out to the US Navy and private sector for help.

Mike Mulroy, a former US undersecretary of defence, told the BBC that specialised US Navy remote submersibles would likely be the only vessels capable of tethering with the submarine and dragging it to the surface.

Among the five people on board the Titan, four people so far have been confirmed - Hamish Harding, a 58-year-old British businessman and explorer, British businessman Shahzada Dawood, 48, and his son, Suleman Dawood, 19, and 77-year-old French explorer Paul-Henry Nargeolet.

Mr Harding announced he was joining the team earlier this month, and said that the crew on the vessel includes "a couple of legendary explorers, some of which have done over 30 dives to the RMS Titanic since the 1980s".

Mr Harding is the chairman of Action Aviation, an international company which deals with sales and operations in the business aviation industry, based in Dubai, United Arab Emirates.

The Explorers Club, of which Mr Harding is a founding member, shared an upbeat message after sounds were detected, saying the "likely signs of life" were a "cause for hope".

French explorer Paul-Henry Nargeolet was also on board, a family spokesman told the BBC. The explorer, nicknamed "Mr Titanic", is a former French navy diver and has reportedly spent more time at the wreckage of the Titanic than any other explorer.

OceanGate - the firm behind the dive - has also confirmed that chief executive Stockton Rush was on board the sub when it went missing.

OceanGate Expeditions charges guests $250,000 (£195,270) for a place on its eight-day expedition to see the famous wreck, which sits 3,800m (12,500ft) beneath the surface at the bottom of the Atlantic.

The site is about 600km (370 miles) off the coast of 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.

Each expedition lasts eight days, according to OceanGate, and each dive 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.

Submarine expert Prof Alistair Greig from University College London has worked through a number of scenarios for where the missing submersible might be, he told BBC Science Correspondent Pallab Ghosh.

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

If it has gone down to the seabed and can't get back up under its own power, the options - according to Prof Greig - are very limited.

"While the submersible might still be intact, if it is deeper than more than 200m (656ft) there are very few vessels that can get that deep, and certainly not divers. The vehicles designed for navy submarine rescue certainly can't get down to anywhere near the depth of the Titanic."

The Titan is a five-person submersible built to descend to depths of 4,000 metres (2.5 miles) and travels at three knots - that's about 3.5 miles per hour.

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".

According to OceanGate's website, the five-person sub has a system for monitoring the vessel's hull in real time.

It has sensors to analyse the effects of changing pressure on the sub as it dives, in order to assess the integrity of the structure.

"This onboard health analysis monitoring system provides early warning detection for the pilot with enough time to arrest the descent and safely return to surface," the company says.

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.

David Pogue, who went on board, reported that he read a waiver that described the submersible as an "experimental" vessel, "that has not been approved or certified by any regulatory body, and could result in physical injury, disability, emotional trauma or death".

Mr 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.

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