A piece of the space shuttle Columbia lies on the side of Hwy 21 near Nacogdoches, Texas, February 1, 2003. Debris from space shuttle Columbia rained down onto fields and highways in Texas on Saturday, with witnesses coming across smoldering metal wreckage, including what appeared to be a door from the orbiter, local officials and eyewitnesses said. REUTERS/Richard Carson
I had the priviledge of seeing the shuttle Columbia several years ago.... up close...I was in the building where it was being worked on. We were able to stand right next too it.
Our group, which was given the tour by a project director, was able to hold a "sample" of a heat tile.
The picture you posted looks like the surface area where the tiles are attached. Those whitish burned places look like the tiles...sort of burned or melted. The squares appear to be the places where other tiles where at one time.