Whereas sonar could not distinguish man-made debris on the sea bed from natural objects, cameras could. The debris field would also be a far bigger target, stretching one nautical mile (1.9 kilometres) or longer, whereas Titanic itself was only 90 feet (27 m) wide.[35] The search required round-the-clock towing of Argo back and forth above the sea bed, with shifts of watchers aboard the research vessel Knorr looking at the camera pictures for any sign of debris.[36] After a week of fruitless searching, at 12.48 am on Sunday 1 September 1985, pieces of debris began to appear on Knorr's screens. One of them was identified as a boiler, identical to those shown in pictures from 1911.[37] The following day, the main part of the wreck was found and Argo sent back the first pictures of Titanic since her sinking 73 years before.[38] The discovery made headlines around the world.[39]