A tile fragment containing mysterious orange specks may provide vital clues in the investigation into the Columbia space shuttle disaster, say officials.
The tile find supports the theory that the shuttle was damaged on take-off
The tile was found near the town of Powell in north-east Texas.
"This is not re-entry heat damage," retired admiral Harold Gehman who is heading an independent investigation into the disaster told reporters.
Some experts say the Columbia was damaged about 82 seconds after lift-off on 16 January when a piece of orange foam broke away from the shuttle's fuel tank smashing into the left wing.
Last week, Boeing released analysis indicating that the Columbia may have been hit not by one but three pieces of the solid foam.
If a tile, such as the one found in Powell, Texas, had been loosened by that impact and then come off during re-entry, the bare aluminium of the shuttle's wing would have been exposed.
That area is roughly the same size of the breach that investigators believed opened and allowed hot gases to enter moments before the shuttle was lost.
Sensors picked up a rapid rise in temperature in some parts of the shuttle's left wing.
Nasa officials also say radar information shows a 12-inch-square (30-centimetre-square) item drifting away from the shuttle on the second day of its flight.
Three days later, the lightweight object re-entered the atmosphere and disappeared over the South Pacific, so it will probably never be determined whether or not it came from the shuttle.
Harold Gehman is puzzled by the orange marks
The collision theory is "just one of many theories, and it's not a favourite of anybody's", said head of the National Aeronautics and Space Administration Sean O'Keefe, reports AFP news agency.
Investigators have also found a partly damaged videotape of the astronauts as they made their descent.
The 13 minutes of the tape which have been restored show members of the crew preparing for landing.
Families have been shown the tapes.
All seven crew members were killed when the Columbia disintegrated in the sky over Texas on 1 February.
A tenth of the space shuttle has now been recovered.
A piece of a tile from the upper side of the left wing found near Littlefield, Texas, is thought to be the most westernmost piece of shuttle debris recovered so far.
"The data and twisted metal are speaking to us. We're just developing ears to hear," Nasa Ames Research Centre director Scott Hubbard said, reports AFP.