Washington (Agencies via Xinhua) -- Unusual formations on the surface of Mars -- including a huge rock shaped like a human face -- may have been carved by a lost civilization or could be just "a trick of nature," four scientists said on Thursday.
In either case, they said, the mysterious outcroppings demand further scrutiny by spacecraft.
The scientists said that a photograph taken of the Martian surface in 1976 by the United States space agency's Viking spacecraft clearly shows a face two kilometers long that could have been carved out of a Martian mountain half a million years ago.
The Sphinx-like image that stares outward from the planet may be part of a complex, as evidenced by other unusual formations nearby, which was built by a civilization that has since disappeared, the scientists said.
Or, they admit, it could all be "a trick of light and shadow".
Brian T. O'Leary, a former US astronaut and expert on Mars, said there is sufficient uncertainty about the origin of the rock face that should make it a major target for future spacecraft sent to Mars.
O'Leary said that Soviet space scientists were preparing to send probes to the planet to examine the area but that their spacecraft was not technically designed to study the site, the Cydonia region.
The news conference on Thursday was prompted by a study of the Viking photographs conducted by Mark Carlotto, an optical engineering expert.
In an article published in Applied Optics, Carlotto said that a computer enhancement of the Viking photographs shows that the face and various other nearby features appear to have been carved by "intelligent design" and not by the random forces of nature.
Carlotto said at the news conference that a sophisticated statistical study of the shapes, compared with other outcroppings on Mars, shows that "the face is not natural."
"It's extremely unlikely that it's a trick of light and shadow", said Carlotto.
Richard Hoagland, founder of an organization of scientists called "The Mars Project", said that the National Aeronautics and Space Administration (NASA) found the face-like stone formation in the Viking photographs more than a decade ago, but dismissed it.
Hoagland, however, said he has studied the photos for years and has discovered that in addition to the face there is "a complex of unusual objects" that he believes could have been built by "intelligent beings".
Randolfo Pozos, the executive director of?????? said that
members of the organization are devided about the origin of the face on Mars.
"Some of our group feel this is a lost civilization", he said.
"Others think it is just an interesting geologic [sic] formation."
NASA plans to launch an unmanned probe, called the Mars Observer, in 1992. Hoagland said it will have a camera onboard that could possibly settle the question about the origin of the stone features on the planet.