US Air Force images of Columbia taken a minute before it broke apart show major damage to the shuttle's left wing, reports said this evening, as NASA held a new memorial to the lost crew.
Hundreds of space agency staff held a special service for the seven Columbia astronauts on the Florida runway where they should have landed February 1st.
The National Aeronautics and Space Administration (NASA) confirmed that accident investigators were studying critical video and photo images of Columbia's last moments and that a "significant" part of one of the wings had been found.
But they did not say if reports of serious damage had been confirmed. High-definition images take by the Air Force as it tracked the space shuttle across the US show that the left inboard wing is jagged near where it begins to intersect the fuselage, according to Aviation Weekand Space Technology, which cited sources close to the investigation.
"The ragged edge on the left leading edge, indicates that either a small structural breach - such as a crack - occurred, allowing the 1370C reentry heating to erode additional structure there, or that a small portion of the leading edge fell off at that location," the article said.
"Either way, the damage affected the vehicle's flying qualities as well as allowed hot gases to flow into critical wing structure - a fatal combination."
NASA deputy administrator Mr Michael Kostelnik told a briefing that Air Force photos and other imagery were taken from the ground in the southwestern US "within the time period when the anomalies in the left wing are occurring."
But he added: "It would be speculative to judge what those photos show." Mr Kostelnik said a "significant" part of the leading edge of one wing had been found near Fort Worth in Texas but again gave little detail except to say it was large enough to analyze.
NASA investigators say that as Columbia re-entered the Earth's atmosphere, temperatures rose significantly on the left side of its fuselage, especially around the wheel well. Its autopilot tried to compensate for increased drag on the left wing, firing steering jets to right the space shuttle and keep the vehicle pointed straight ahead.
Investigators are looking into whether a piece of foam insulation that broke off one of Columbia's external fuel tanks on liftoff January 16th, and hit the underside of the left wing, could have played a role.
AFP