What Could Have Happened to the Missing 'Titan' Sub? Experts Share 5 Possible Outcomes

What exactly happened to the Titan?

It’s the question being asked around the world as more information emerges about the Titanic-seeking submersible, which has been missing since Sunday.

Experts have been offering their hypotheses as the search continues for OceanGate Expeditions’ sub and the five passengers, who were traveling down to the wreckage when they lost contact with Canadian expedition vessel Polar Prince.

“I think that it is important to understand that this is a very, very extreme mission," Ofer Ketter, a submarine pilot and expert who co-founded companies such as Origen Extraordinary Escape and Submerge, tells PEOPLE. "This is not a normal tourism submersible dive."

But time is running low for the passengers. At a press conference in Boston on Tuesday, United States Coast Guard Captain Jamie Frederick said the sub started its expedition with about 96 hours worth of oxygen. As of Wednesday, that number has dwindled to less than 24 hours to find the vessel.

Here are five theories that experts say could explain what happened to the Titan:

Implosion

Experts agree: This is the worst-case scenario. None of the victims would have survived what many describe as a “catastrophic” event.

An implosion would have likely been caused by the failure of its pressure housing, according to Stefan B. Williams, a professor of marine robotics at the University of Sydney in Australia.

Williams told The Guardian that a catastrophic failure of the pressure system would be “like a small bomb going off.”

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“Although the Titan’s composite hull is built to withstand intense deep-sea pressures, any defect in its shape or build could compromise its integrity — in which case there’s a risk of implosion,” Williams wrote in a blog post shared on The Conversation.

Dr. David Gallo, a senior adviser with RMS Titanic Inc., shared a similar analysis in an interview with Sky News. “A catastrophic implosion of the sub itself, which would be horrific,” he said. “There's no coming back from that.”

In fact, Dr. Gallo believes implosion is the most likely cause of the sub’s disappearance. “I don't know how else you can disappear that quickly,” he added.

Fire

Despite being underwater, experts say it is possible that a fire may have broken out within the vessel — and could have been disastrous in numerous ways.

Eric Fusil, an associate professor and director of the shipbuilding hub at the University of Adelaide, told the Associated Press that a fire could “create toxic fumes that could render the crew unconscious.”

A blaze could also possibly “compromise the vehicle’s electronic systems” used for navigation and control, Williams said in his blog post. “Fires are a disastrous event in enclosed underwater environments,” he added.

Lost at sea, at the surface

It is also possible that the Titan is floating somewhere on the surface of the Atlantic Ocean and has yet to be spotted.

Though this is one of the best-case scenarios, the passengers are still at risk of running out of oxygen. The vessel is bolted from the outside, and passengers have no ability to open the door from the inside.

“You can’t get out unless somebody unbolts it,” Fred Hagen, who has previously visited the Titanic wreckage on the Titan, told PEOPLE on Tuesday.

Lost at sea, underwater

The Titan may also be lost at the bottom of the ocean, which experts believe is a much more concerning scenario.

Ketter tells PEOPLE that a power outage is one example of “a serious mechanical or technical failure” that could have occurred inside the submersible. The passengers may also have “passed out” due to low oxygen levels in the sub.

The sub started with 96 hours of breathable oxygen, and is now believed to have less than 24 hours left.

A press conference in Boston on Wednesday, United States Coast Guard Captain Jamie Frederick confirmed previous reports that suggested a Canadian P-3 “detected underwater noises” while searching the area. 

Frederick said “several P-3 flights heard noises” in the area, but that an initial ROV search of the area “yielded negative results.”

But crews remain hopeful that they will locate the missing sub before it runs out of oxygen. “This is a search and rescue mission 100 percent,” Frederick told reporters.

Stuck in the Titanic

The submersible may have also gotten stuck somewhere in the Titanic’s wreckage — which has happened before to a different vessel. Williams told Insider that the scenario is unlikely, but not impossible,

Frank Owen, a retired Royal Australian Navy official who also worked as submarine escape and rescue project director, told The Guardian that “debris from the disaster” covers the ocean floor.

“There are parts of it all over the place. It’s dangerous,” Owen explained.

ABC News reporter Michael Guillen was aboard a Russian submersible in September 2000 when the vessel became lodged within the wreckage after a current pushed it into the blades of the Titanic's propeller.

Guillen recalled fearing for his life as he and others remained quiet for nearly an hour while the pilot attempted to maneuver the vessel out of its precarious position.

Eventually, the submersible wriggled free, but Guillen knows it could have ended much differently.

“I remember very clearly, in fact, that this voice came into my head — and I'll never forget it for the rest of my life — it said, 'This is how it's going to end for you,' " Guillen told ABC News on Tuesday.