They reckon that the broken bit let in really hot gases when the shuttle tried to land, and those gases led to the shuttle breaking up - killing seven astronauts.
A Nasa spokesman shows a model of the shuttle's wing
Video footage of the shuttle launching showed a piece of foam striking the left wing, but the experts haven't said that was the cause of the broken seal or panel.
Tests are now being done to work out if that piece of foam was the reason why the shuttle exploded.
The experts are firing pieces of foam at actual shuttle parts to see how much damage they do.
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