'Angel of 9/11': Steel visage tricks the eye — and touches the heart with hope.

It’s called “Impact Steel," a twisted girder from the North Tower of the World Trade Center that is now housed at the National September 11 Memorial and Museum. If you look closely you’ll see what appears to be a shadowy face of an angel within the metal.

The steel column came from precisely the place on the north tower, in between the 93rd and 99th floors, where a hijacked plane struck and exploded into flames more than 12 years ago.

Many who viewed this piece of steel at the museum say they see the outline of a woman's face near the top of the mangled artifact.

"You can see the face clear as day, as if it’s looking down over a sacred spot," a visitor said. Some workers have even started referring to the visage as the "Angel of 9/11."

Experts say that the face is the result of corrosion. 

An angel appears out of the wreckage of 911

Construction workers at the National September 11 Memorial and Museum at New York's ground zero are reporting that they can see a sad-looking face that's been dubbed the "Angel of 9/11," seemingly emerging from the twisted steel of a girder that was hit by the first hijacked plane. The face like feature is the result of natural corrosion plus a trick of the eye — but that shouldn't make the angel any less inspiring.

The angel's dark eyes, nose and open mouth stem from a combination of factors, starting with the way the steel was twisted when American Airlines Flight 11 slammed into it on the morning of Sept. 11, 2001.

After the 911 attack, salts, oxides and moisture on the steel's surface affected how the girder corroded, said P. Chris Pistorius, a materials scientist at Carnegie Mellon University who is co-director of the Center for Iron and Steelmaking Research. Air circulation around the ruined steel played a role as well.

"Atmospheric corrosion is very sensitive to microclimates" he reported. "It's actually difficult to get even corrosion of such a surface. It's more likely to get a pattern than to get uniform corrosion."

If layers of steel are lying on top of each other, as appears to have been the case with the 9/11 girder, moisture can "wick in different areas and leave all kinds of different patterns," said Thomas Eagar, a professor of materials engineering at the Massachusetts Institute of Technology.

Pareidolia at work

The pattern of twisted, corroded steel looks like a face in large part because of a perceptual phenomenon known as pareidolia, a term derived from the Greek words for "mistaken image." It's the same phenomenon that's behind the Face on Mars, New Hampshire's Old Man of the Mountain, the Virgin Mary cheese sandwich and the "cloud angel" that was spotted over Florida when Pope Francis was chosen.

Our brains are well-suited to finding patterns even in seemingly random patches of light and dark — and that's how the corrosion gave rise to the Angel of 9/11.

Many visitors to the 9/11 Memorial and Museum have marveled over the sight. "You can see the face clear as day, as if it’s looking down over a sacred spot," one visitor who toured the exhibit in advance of its public opening said.

"People often find meaning in tragedy," a spokesperson for the memorial museum stated. "For us, this piece of steel is historically important to include in the museum, as it helps to tell the story of 9/11."

After looking at a photo showing the angel, Pawan Sinha, a neuroscientist at MIT who specializes in visual recognition, agreed that the face is a "compelling example" of pareidolia at work.

Experts say that as long as the girder is being kept under climate-controlled conditions, the corrosive process should be held in abeyance — ensuring that the angel will endure. You can see for yourself when the museum opens to the public next year in New York at the site of the 911 Memorial.

Nancy Burban 2013

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