HOUSTON — NASA broadened its investigation Sunday into radar data showing an object rapidly leaving the vicinity of Columbia on the second day of its mission, and raised the possibility that a wastewater pump could have formed a block of ice that dislodged and damaged the shuttle.
Evidence of the object turned up Saturday, officials said, as Department of Defense analysts scoured radar images they had recorded during Columbia's ill-fated mission.
It remained unclear, NASA said, what the object was or whether it ultimately caused the shuttle to break apart as it reentered the Earth's atmosphere Feb. 1.
NASA officials said it was possible that the object was not space junk, as several analysts surmised, but a block of ice.
Ice was first encountered as a problem during a mission nearly 20 years ago, when the end of a device designed to emit urine and other waste from the space shuttle froze.
NASA officials suggested Sunday that the wastewater pump could have formed a block of ice that dislodged Jan. 17, a day after the shuttle lifted off from Cape Canaveral, Fla. The ice could have damaged the shuttle or the shield of heat-resistant tiles designed to protect it from the soaring temperatures encountered during reentry.
Several former NASA officials said Saturday that evidence of an object "in the vicinity" of the space shuttle could point to the theory that Columbia was struck by space junk or a small meteorite. An impact like that, even by a small object, could have damaged the shuttle enough that its tiles began to "zipper" open during reentry.
NASA is investigating that theory.
The object was first detected by the Air Force Space Command, which operates a bank of radar and optical telescopes that track an estimated 8,500 pieces of man-made debris in space, each as large as a baseball.
Discussion of the debris continued to shift the focus from a piece of foam insulation that broke off an external fuel tank and struck the shuttle near its left wing during liftoff.
That incident was viewed as a possible culprit in the days following the accident, which killed Columbia's seven-member crew.
Although it still remains a focus of the investigation, top NASA officials said late last week that they do not think the block of foam could have done enough damage to the craft to cause its destruction.