Could New Flight 370 Satellite Photos Be Nothing but Ocean Junk?

Aircraft and ships will return to remote seas off Australia on Friday, searching for floating objects spotted by satellite that Malaysia's government called a "credible lead" in the hunt for a missing jetliner.

But oceanographers have been quick to point out that oceans are full of debris, and that this new lead could turn out to be something as mundane as a shipping container washed overboard.

"It could be lots of things," said Dr. Simon Boxall, a lecturer at the British government-funded National Oceanography Centre in Southampton.

"There are around 10,000 containers washed over the sides of ships and quays each year and that could be exactly what we are seeing here."

Jason Middleton, an aviation professor at the University of New South Wales in Sydney, agreed with this theory.

"The chances of it being debris from the airplane are probably small, and the chances of it being debris from other shipping are probably large," he told The Associated Press.

But the larger of the two objects — judged to be some 78 feet in length — was far too big to match the size of any shipping container in use, according to industry journalist Janet Porter.

Porter is editor in chief of containers at the London-based shipping magazine Lloyd's List. She said the largest container in use anywhere in the world was 45 feet, almost half the size of the unidentified object.

"If the object is more than 70 feet long, then it cannot be a shipping container," she told NBC News Thursday. "You would know if your ship lost something that large."

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She also disputed the figure of 10,000 containers being lost each year. "That figure was used once a while back and it seems to have entered into folklore," she said. "Containers do get washed into the sea, but it's not as many as that."

The largest single loss of shipping containers happened on Feb. 14 this year, Porter said, when a container ship, the Svendborg Maersk, lost some 520 units in rough weather in the Bay of Biscay between France and Spain.

But these containers are not the only objects found at sea. Five million tons of debris was created by the 2011 earthquake and tsunami off Japan, according to Japanese government estimates. Although 70 percent of it sank quickly, the remainder floated as far away as the west coast of the United States.

In June 2012, a nearly 70-foot-long dock floated onto an Oregon beach after being torn loose from a fishing port in Japan. A starfish native to Japan was found clutching to the structure.

Boxall said one piece of evidence which did give credence to the theory that this was part of Flight 370 was the presence of a possible oil slick in one of the images. But he warned there were lots of other things that could give this effect other than a crashed plane, such as a leak from a container of even a shoal of fish glinting in the sun.

NBC News' Alastair Jamieson and The Associated Press contributed to this report.