An astronaut who's flown five missions in space and climbed Mount Everest has just wrapped up a scientific mission to what divers call the "Mount Everest of Shipwrecks," the S.S. Andrea Doria.

It's a "huge bucket list thing," admits Scott Parazynski, who co-piloted the five-person crewed submersible Cyclops I to the wreck, which lies off the coast of Massachusetts at a depth of more than 200 feet (61 meters).

The weeklong expedition to the Andrea Doria, organized by submersible company OceanGate, was designed to collect information on the current condition of the wreck. Researchers on return trips to the wreck will use that information to better understand how modern shipwrecks decay in marine environments.

While bad weather cut the expedition short, a news conference revealed that the wreck has experienced significant decay in the two years since the last images of the Andrea Doria were captured, and that the entire superstructure of the 697-foot-long (212-meter-long) vessel has collapsed.

An Iconic Maritime Tragedy

The luxury Italian liner Andrea Doria sank off the coast of Nantucket in July 1956 after being struck by the Swedish liner M.S. Stockholm. While the Andrea Doria managed to stay afloat for more than 11 hours after being struck, 46 people died in the collision. Media coverage of the ship's sinking and its aftermath helped make the Italian liner synonymous with 20th-century maritime disasters.

View Images The submersible Cyclops I is shown here aboard its Mobile Subsea Launch and Recovery System ( MSLARS ) during a 2015 expedition in the Gulf of Mexico. On its expedition to the Andrea Doria, it carried sonar and imaging equipment to record the shipwreck. Photograph courtesy OceanGate Inc.

Now, 60 years after the liner's sinking, the wreck is collapsing as a result of environmental conditions and fishing activity.

The top of the wreck, which was originally in about 160 feet (48.8 meters) of water, has now dropped below 200 feet (61 meters). The majority of the structure is about 240 feet (73.2 meters) deep.

The continued decay of the Andrea Doria means that the shipwreck is becoming more elusive and dangerous to scuba divers. Where it's now located is at least 70 feet (21 meters) deeper than suggested maximum depth for recreational divers.

Advanced divers using technical gear and mixed breathing gas can stay less than 20 minutes on the wreck, in conditions that involve strong currents and low visibility. The dangers involved in exploring the remains of the iconic vessel have led divers to dub it the "Mount Everest of Shipwrecks."

Sixteen people have died while diving the Andrea Doria, including a neuroscience professor who disappeared on the wreck in 2015.

What Decaying Wrecks Do to Our Oceans

By using a crewed submersible, researchers were able to safely spend hours exploring the wreck site, where they collected sonar data that will be used to create a very high resolution , 3-D model of the vessel remains to serve as a baseline for future visits to the Andrea Doria. This will help scientists better understand how shipwrecks deteriorate and how that decay may impact the marine environment, says OceanGate CEO Stockton Rush.

View Images In this top-down sonar scan from the Andrea Doria expedition, the ship's bow is visible on the left with a port rail extending to the right. The seabed around the wreck shows evidence of scouring by strong undersea currents. Photograph courtesy OceanGate Inc.

"Steel ships with aluminum superstructures, like the Andrea Doria and so many wrecks from World War II, are very common and potentially polluting," says Rush. "There's a lot about their decay processes that are not well understood."

From the Bottom of the Atlantic to Seas of Europa

While seeing the remains of the Andrea Doria with his own eyes may be a boyhood dream of astronaut Parazynski, there's a bigger reason why he's co-piloting the vessel that took him to the wreck.

"We can take these types of technologies to explore extremophile life in the oceans," he says, which will in turn help us evaluate the possibility of life in extreme environments on other planets.

View Images Astronaut Scott Parazynski, shown here during a 2007 space walk, believes the best exploration "takes place as a human-robotic partnership." He's confident that submersible technology can help us find extraterrestrial life. Photograph by NASA

"For instance, what might lie in the waters under the icy crust of [Jupiter's moon] Europa? If we can someday drop a submersible through the ice and swim around there, would we find extremophile life there as well?

"There's just a great synergy going on right now between ocean exploration and space exploration," says Parazynski.

Just as importantly, being part of a crewed mission on a submersible brings advantages to explorers that piloting a remotely operated vehicle (ROV) from topside doesn't offer.

"My firm belief is that the best exploration takes place as a human-robotic partnership," says the astronaut, who has performed seven space walks during his five missions with NASA.

"It's like having MacGyver in the loop; it's about real-time problem solving that really can save the day when it comes to extreme exploration."