The Australian Defense Force vessel Ocean Shield detected more pings on Tuesday raising hopes that the search for the missing Malaysian Airlines Flight MH370 is getting closer in a search area of more than 77,000 square kilometers.

The retired Australian defense forces chief, Angus Houston, who is coordinating the search, remains optimistic.

The ocean floor where the search is now being conducted off western Australia is covered in silt. The bottom is 4,600 meters down, where pressures are massive. The depth raises special difficulties for recovery if the wreckage is found.

We know, at least, that the black box flight and voice data recorders will become more difficult to locate as their batteries wane and signals grow fainter.

While much has been said and written about the search, there is another side to the mystery. According to the distinguished oceanographer Tony Haymet, weeks of precious time could have been saved had it not been for the distraction of various man-made floating objects.

"Much of what was being detected from satellites, actually turned out to be junk … much of it discarded plastic … human junk," the director emeritus and professor at Scripps Institution of Oceanography at the University of California said.

Although he is not involved in the search for MH370, the former chief of Australia's national science research agency's marine and atmospheric division and visiting scholar at the US Studies Centre at the University of Sydney, was able to make some observations.

"During the initial stages, a lot of time was taken up searching vast areas of the Indian Ocean for objects detected by satellites," he said. "None of it was related to the flight, and it turned out to be garbage, much of it plastic … small pieces of plastic that had been churned by the ocean into a sort of thick soup that doesn't go away.

"It was a huge distraction, initially, and took up a lot of man hours before the pings were detected."

The garbage created many false leads, he said.

"I think we as human beings have some responsibility here as it raised so many hopes, especially among the relatives and friends, only to have them dashed.

"Even if there was a part of a wing floating among this, I doubt whether we could have distinguished it from all the other junk."

Why can't satellites differentiate between junk and wreckage?

"I don't know. Perhaps the military may have an answer on that," Haymet said.

"Even so, without my knowing the specific density of, say, a Boeing 777's wing, much of this would probably be floating just beneath the ocean's surface making it very difficult to detect.

"I'm not surprised nothing from the aircraft has been identified. Ships lose containers at sea all the time. They don't float on the surface but just below it. Ships can't see them," he said.

Haymet said that even if a debris field is found, it would be at such a depth that it would take a "long, long time" to recover it.

"So far, there has been no surface debris — no life jackets or seat cushions. That puzzles me. If you didn't have the human garbage floating around I think you would have had a much better chance of finding floating debris from the aircraft.

"Now, it has probably dissipated, and you may never find anything," he said.

The next big test will be locating the black box and recovering it, Haymet said, but added that it might never be recovered. "It is very difficult and very expensive to work in the sort of depths they are talking about in the Indian Ocean."

Haymet said the search for Air France Flight 447 that crashed into the Southern Atlantic Ocean in 2009 was made easier because searchers "had a much better idea of its track, and Air France was determined to spend whatever it took and to use whatever robots that were available to find it."

With MH370 there is no precisely known flight path, and the search area covers a large expanse of ocean. There is no wreckage, but the detection of pings indicates that searchers may be closing in on the aircraft.

"With the Air France flight, the conditions were better," Haymet said.

And it took two years to find the black box.