— The "Face on Mars" is revealed as a lumpy hill in this new view with a resolution of 13.7 metres per pixel. Mission scientists reconstructed the 3D shape of the hill using data from Mars Express's stereo camera and overlaid it with fine surface details from Mars Global Surveyor's Mars Orbiter Camera (Image: ESA/DLR/FU Berlin/G Neukum/MOC/MSSS)
Light and shadow play across a hill in this 1976 Viking image, giving the appearance of a face (Image: NASA)
Another view of the "Face on Mars" hill is seen in this Mars Express view. Giant slabs of rock have slipped down the sides of the 1-kilometre-tall hill to give it a cracked eggshell appearance (Image: ESA/DLR/FU Berlin/G Neukum)
New images of the "face" on Mars have been obtained by Europe's Mars Express spacecraft. They reinforce what scientists thought from the beginning that the face is just a naturally sculpted hill.
The "face" appeared in a photo of Mars's Cydonia region taken in 1976 by NASA's Viking 1 spacecraft. NASA scientists believed from the beginning that the feature was simply a hill that happened to look like a face because of the way the Sun cast shadows across it at the time the photo was taken.
However, the image sparked speculation that the face was built by aliens and that NASA was trying to cover it up.
The agency used the Mars Global Surveyor spacecraft to take new images of the region in 1998 and 2001. The new, much more detailed images showed a hill with no particular resemblance to a face (see Martian conspiracy theorists lose face).
But since the European Space Agency's Mars Express spacecraft arrived at Mars in 2003, many unconvinced members of the general public have been asking mission scientists to take more images of the feature.
"So many people wrote me emails hundreds saying, 'Why don't you image Cydonia, tell us the truth, we don't believe NASA,'" says Gerhard Neukum of the Free University of Berlin, Germany, chief scientist for Mars Express's High Resolution Stereo Camera (HRSC).
Mission controllers have been trying to get images of the region since 2004 but had been thwarted until recently by dust and haze in the atmosphere. Finally, on 22 July 2006, the team obtained clear images of the region with the HRSC.
By making observations of the area from slightly different angles as the spacecraft moved through its orbit, mission scientists have been able to build a 3D map of the "face" and the surrounding area.
Sculpted by erosion
The hill that sparked so much speculation is clearly seen in the new images to be a natural feature shaped by erosion, says Agustin Chicarro, ESA's chief scientist for Mars Express.
"My grandfather used to collect pieces of wood that look like birds or dogs or things like that," he told New Scientist. "This is the same thing people get excited and see what they want to see. What has modelled these reliefs is simply erosion."
Neukum agrees. "Its a mountainous structure and there's no artificial thing. These are mounds that have survived a general erosional process," he told New Scientist.
The whole area was once as high as the tops of the hills in the region, he says, but most of it has eroded down, with a few more resistant areas surviving as hills. The erosion is probably the result of ancient glaciers or perhaps liquid water carving into the rock, he says.