The mysterious object drifted through space for two days before reentering the atmosphere. As reported earlier by SPACE.com, a data processing error prevented Air Force analysts from recognizing that the object had come from Columbia - and then only after the space plane and its crew were lost on February 1.

CAIB study teams are looking into the prospect that a damaged section of Columbia's thermal protection system may be the object seen by radar. NASA has supplied nearly 30 different shuttle-related items, used in radar signature tests to help pinpoint what the free-floating hardware may have been.

Ground testing has included portions of a shuttle's leading edge wing material, made of reinforced carbon-carbon, and other related hardware, such as a carrier panel, said Tyrone Woodyard, a CAIB spokesman.

Woodyard told SPACE.com that radar signature tests are still underway, with a few other possible candidate items recently added. "They have one or two pieces of the shuttle they want to take through tests before they confidently conclude that [the object] was most likely a carrier panel," he said.