[Jael]

"The big question is what might have caused the anomalies seen in the left wing. About 80 seconds after Columbia blasted off Jan. 16, long-range tracking cameras show what appears to be a sizeable piece of insulation from the shuttle's external fuel tank breaking away and hitting the underside of the left wing. Engineers today said the piece measured 20 inches across in its largest dimension."

http://spaceflightnow.com/shuttle/sts107/030202investigation/

[#3Fan]

"The big question is what might have caused the anomalies seen in the left wing. About 80 seconds after Columbia blasted off Jan. 16, long-range tracking cameras show what appears to be a sizeable piece of insulation from the shuttle's external fuel tank breaking away and hitting the underside of the left wing. Engineers today said the piece measured 20 inches across in its largest dimension."

Yeah, it was big. If it was ice, then it was massive.