There's a lot of speculation swirling around the internet about the missing Titanic-bound submersible. But one thing is ?? ??? ?? ??certain: The submersible's deep sea communication wasn't dependent on SpaceX's satellite internet product, Starlink.

The belief, suspicion, or confusion about Starlink's role in the lost Titan craft, which is holding five passengers in cramped quarters, was likely triggered by a now-deleted tweet from OceanGate, the company which operates the submersible. "The wreck of the Titanic lies about 400 miles off the coast of Newfoundland. Without any cell towers in the middle of the ocean, we are relying on @Starlink to provide the communications we require throughout this year’s 2023 Titanic Expedition," the tweet read. Another tweet, from SpaceX's Starlink account in early June, reads "Internet from space supporting Titanic dive expedition."

Indeed, the vessel that ferried the Titan to the middle of the sea would benefit from satellite internet to communicate on the surface, use phones, post on social media, and beyond. The deleted tweet shows people on a laptop, presumably aboard the hired Canadian vessel taking the Titan, and its passengers, to a deep ocean dive site.

But when they're deep underwater, submarines and submersibles do not use satellite internet to communicate with the surface above. These craft rely on sound waves (a type of "mechanical" wave) to communicate simple messages like location from the dark depths. It's a technology called sonar, which is short for "sound navigation and ranging." Light waves, such as radio waves, don't transmit through deep waters, especially miles down.

"The Titan would have had an acoustic link with its surface vessel, set up through a transponder (a device for receiving a sonar signal) on its end, and a transceiver (a device that can both transmit and receive communications) on the surface vessel," Stefan Williams, a professor at the University of Sydney who develops marine robotic systems, wrote in The Conversation, a site that publishes articles written by academics and researchers.

Sound waves need to travel through a medium, like an atmosphere or water. Radio waves, which Starlink uses, can easily pass through the vacuum of space and the atmosphere, but not through water, especially deep water. The Titanic lies some 12,500 feet beneath the surface.

"Water turns out to be a fantastic medium – albeit a slow one – for carrying mechanical waves long distances, making Sonar the top choice for underwater object detection," writes the Carnegie Museum of Natural History.

(Ongoing research could one day make deeper-water WiFi a reality, though it's unknown how well it would work, and at what depths.)

Importantly, OceanGate is currently involved in a serious rescue mission, and it's still unknown what has happened to its Titan submersible. Many questions remain about how its overall operations, including its communications on the surface, impacted the mission gone awry, and potential tragedy.

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It's possible the submersible lost power. Its hull could have been compromised. What is known, however, is OceanGate was once sued by a former employee over safety risks, which was first reported by The New Republic. The suit highlighted some potentially major design flaws.

A multinational effort continues the search on Wednesday, both on the ocean surface and below, for the missing submersible and its passengers. Their sonar isn't working, and any oxygen supply is fast diminishing.