Washington Photos from a satellite orbiting Mars suggest the Red Planet was once a water-rich land of lakes, boosting the theory that billions of years ago it may have had the conditions needed for the evolution of life.
The photos, taken by the Mars Global Surveyor spacecraft, show massive sedimentary deposits, with thick layers of rock stacked one on top of another in miles-deep formations.
In the wall of a massive canyon that stretches for thousands of miles, there are sharp layers of rock, rather like the formation that causes a striped pattern on the walls of Arizona's Grand Canyon, said Kenneth S. Edgett, a co-author of the study in Science.
"I don't know how to do that (form such layers) without water," said Edgett at a news conference Monday at NASA's Jet Propulsion Laboratory in Pasadena, Calif. He said the layering could possibly have been formed by other means, such as wind or volcanism, "but water is the leading candidate."
Michael C. Malin, lead author of the study, said that "the regularity of the layering is hard to create" without the presence of water.
The researchers both are with Malin Space Science Systems in San Diego.
Malin, the principal scientist using a camera on the Mars Global Surveyor, said the photos suggest that water may have seeped in and filled Martian craters that were punched out of the planet surface by impacting asteroids around 3.5 billion years ago.
"My guess is that there were lots of lakes," said Malin. "There may have been some areas that were so wet that there were small seas."
Malin said that the researchers have found no geologic evidence of Earthlike oceans, however.
The layered rock, like that sighted on Mars, would "where you would go to find evidence of life," said Malin. On Earth, sedimentary rock is often rich with fossils.
But not all planetary experts were persuaded by the photos released by NASA.
Alan H. Treiman said he and some other planetary geologists at the Lunar and Planetary Institute in Houston believe the interpretation by Malin and Edgett is not correct.
Treiman, in a telephone interview, said that it already was known that there were layered rock formations on Mars and that the new photos do little to advance the understanding of how such rocks formed.
"It's nice to see the images, but this is not a dramatic new revelation," said Treiman. He said actions other than water volcanism or blowing dust could have formed the layered rock.
"This is not evidence for an early wet, warm Mars," said Treiman. He said the layered rock "is probably not relevant to the possibility of life forming very early on Mars."
However, J. William Schopf, head of UCLA's Center for the Study of Evolution and the Origin of Life, said the study gives strong support for theories that Mars was wetter, warmer and potentially more friendly to life billions of years ago.
"This is the strongest evidence yet for what appear to be sedimentary units on Mars," he said.