Latest Theory--Perhaps a Meteor Hit Shuttle
Nasa says a small meteor or piece of man-made space junk may have struck the Columbia shuttle causing it to crash.
Even a tiny scrap of debris grazing the shuttle could have damaged thermal tiles just enough to start a chain reaction.
The comments by Milt Heflin, the space agency's flight director, cast doubt on the lead theory that a piece of foam insulation damaged the craft during blast off.
"Did we take some hit? That's a possibility. Something was breached," he has told the Los Angeles Times.