HoustonChronicle - Columbia inquiry looks closely at damage to leading edge

Investigators are considering a scenario that begins with a hole or breach in a single panel, allowing hot gases to flow into the wing and sequentially tearing off adjacent panels -- a so-called zipper effect across the leading edge, according to the source close to the investigation.

The theory is supported by several other pieces of evidence. Recovered leading edge panels now at Kennedy Space Center in Florida show that the attachment points were melted, rather than broken. The theory is also supported by a photograph taken by astronomers in Albuquerque, N.M., showing what appears to be a damaged, jagged area of the left wing.