Twenty-five years ago something funny happened around Mars.
NASA's Viking 1 spacecraft was circling the planet, snapping photos of possible landing sites for its sister ship Viking 2, when it spotted the shadowy likeness of a human face. An enormous head nearly 2 miles (3.2 kilometers) from end to end seemed to be staring back at the cameras from a region of the Red Planet called Cydonia.
There must have been a degree of surprise among mission controllers back at the Jet Propulsion Lab when the face appeared on their monitors.
But the sensation was short-lived. Scientists figured it was just another Martian mesa, common enough around Cydonia, only this one had unusual shadows that made it look like an Egyptian pharaoh.
It certainly did!
The "Face on Mars" has since become a pop icon. It has starred in a Hollywood film and has appeared in books, magazines and radio talk shows -- even haunted grocery store checkout lines for 25 years! Some people think the Face is bona fide evidence of life on Mars -- evidence that NASA would rather hide, say conspiracy theorists.
Meanwhile, defenders of the NASA budget wish there was an ancient civilization on Mars. Although few scientists believed the Face was an alien artifact, photographing Cydonia became a priority for NASA when Mars Global Surveyor (MGS) arrived at the Red Planet in September 1997, 18 long years after the Viking missions ended.
"We felt this was important to taxpayers," explained Jim Garvin, chief scientist for NASA's Mars Exploration Program. "We photographed the Face as soon as we could get a good shot at it."
And so on April 5, 1998, when Mars Global Surveyor flew over Cydonia for the first time, Michael Malin and his Mars Orbiter Camera (MOC) team snapped a picture 10 times sharper than the original Viking photos. Thousands of anxious Web surfers were waiting when the image first appeared on a JPL Web site, revealing...a natural landform. There was no alien monument after all.
Still, belief
But not everyone was satisfied.
The Face on Mars is located at 41 degrees north latitude where, at the time of the April 1998 photo, it was Martian winter -- a cloudy time of year on the Red Planet. The camera onboard MGS had to peer through wispy clouds to see the Face. Perhaps, said skeptics, alien markings were hidden by haze.
Mission controllers prepared to look again.
"It's not easy to target Cydonia," said Garvin. "In fact, it's hard work."
Mars Global Surveyor is a mapping spacecraft that normally looks straight down and scans the planet like a fax machine in narrow 1.6-mile- (2.5-kilometer-) wide strips.
"We just don't pass over the Face very often," Garvin said.
"As a rule of thumb, you can discern things in a digital image three times bigger than the pixel size," he added. "So, if there were objects in this picture like airplanes on the ground or Egyptian-style pyramids or even small shacks, you could see what they were!"
What the picture actually shows is the Martian equivalent of a butte or mesa -- landforms common around the American West. "It reminds me most of Middle Butte in the Snake River Plain of Idaho," said Garvin. "That's a lava dome that takes the form of an isolated mesa about the same height as the Face on Mars."
Next page: Laser altimeter shows it's like other mesas
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