Using evidence from that debris and video from takeoff, NASA determined a piece of foam struck the shuttle on take off, puncturing the end of a wing. The intense heat of the shuttle re-entering the earth's atmosphere caused gases to enter the hole in the wing.

Why did the space shuttle explode?

Hot gases from the rocket had slipped past the O-rings in two of the SRB segments. ... At roughly the 73-second mark after launch, the right SRB triggered the rupture of the external fuel tank. Liquid hydrogen and oxygen ignited, and the explosion enveloped Challenger.

Have any space shuttles exploded?

STS-107: Space Shuttle Columbia Disaster

The shuttle broke up catastrophically on February 1, 2003, killing all aboard. The disintegration of the space shuttle Columbia on February 1, 2003, as it reentered the atmosphere was another of the most traumatic accidents in the history of space expedition.