why did challenger explode

just now 1
Nature

The Space Shuttle Challenger disaster occurred because a rubber O-ring seal in one of the right solid rocket boosters failed in the cold conditions at launch, allowing hot gas to escape and breach the external fuel tank. The ensuing structural failure caused the shuttle to break apart shortly after liftoff, killing all seven aboard. This conclusion was established by the Rogers Commission and later corroborated by NASA and independent investigations.