The search for the missing submersible on an expedition to view the wreckage of the Titanic passed the critical 96-hour mark Thursday when breathable air could have run out, a grim moment in the intense effort to save the five people aboard.
The Titan submersible was estimated to have about a four-day supply of breathable air when it launched Sunday morning in the North Atlantic — but experts have emphasized that was an imprecise approximation to begin with and could be extended if passengers have taken measures to conserve breathable air.
And it's not known if they survived since the sub's disappearance.
Many obstacles still remain: from pinpointing the vessel's location to reaching it with rescue equipment to bringing it to the surface — assuming it's still intact. And all that has to happen before the passengers' oxygen supply runs out.