Photos Bolster Possibility of Martian Lakes

The dry, dusty surface of Mars may once have been a Minnesota-like land of lakes, according to vivid new photos of the planet released Monday.

The images do not show water, but capture dramatic layered geological outcrops like those found in the Grand Canyon, that usually form within bodies of water.

The new pictures could radically revise notions of Martian geology, suggesting that the planet was a wetter--and wilder--place than previously believed. They also suggest that water may have been a long-standing feature of the planet and existed for millions of years, long enough for life to evolve.

“To geologists, layering is like the Holy Grail,” said Mike Malin, who heads Malin Space Science Systems, the San Diego company that operates the Mars Orbital Camera now circling the planet aboard NASA’s Mars Global Surveyor. “Mars isn’t the way we thought it was.”

“This picture really blew our socks off,” Ken Edgett, the study’s coauthor and a scientist at Malin, said of an image showing detailed, regularly spaced layers across the bottom of Valles Marineris, a canyon in Mars that stretches across a length equivalent to the distance between Los Angeles and New York. “We looked at that and said, ‘We don’t know how you do that without water.’ ”

The report is to be published in Friday’s issue of the journal Science.

This summer, Malin and Edgett reported finding evidence that small amounts of water may have recently flowed on Mars and carved out gullies within craters. The new finding indicates large amounts of water may have covered parts of the planet billions of years ago.

Signs of layered sediments were first detected on Mars in 1971, with the Mariner 9 mission. The new images are the first highly detailed pictures and show that the layers are distinct from most of the Martian terrain.

The pancake-like layers are widespread, visible in hundreds of the impact craters and deep chasms that scar the planet’s surface. As in the Grand Canyon, erosion exposes layered outcrops far beneath the planet’s surface. The layered rocks date from the earliest part of Martian history, more than 3.5 billion years ago.

Malin and Edgett happily admit that they have only part of the story. They have no idea where the sediments that make up the layers came from or how they could have been so dramatically eroded. They also see no “smoking gun”--traces of gullies or streams that might have carried water to the areas where the sediments accumulated.

“There’s a story there. It’s just calling us,” Edgett said.

An alternative explanation is that the energetic mix of wind and sand that fuels the infamous dust storms on Mars may be transporting the sediments and that cyclic changes in the planet’s atmosphere may play a role in depositing dust. In such a scenario, water would not be required, and the chances of finding traces of life might be diminished.

“Any time you find layered rock, you know some kind of sedimentary process is occurring. The question is, is it sediments that were deposited in water, or in air?” asked Phil Christensen, a professor of geology at Arizona State University who also has an instrument aboard the Global Surveyor. “It’s going to be very difficult to tell from images alone whether it was wind or water that formed those layers.”

Other explanations, such as dust thrown up by craters or rocks spewed by volcanoes, do not explain the widespread extent of the layered sediments, Malin said.

Christensen’s work also suggests that water may have had a role in forming the planet’s geology. His infrared instrument has examined other layered rocks on the planet and found accumulations of the mineral hematite, which is formed in warm water. It will probably take more thermal imaging, high-resolution photos and even a trip to the rock outcrops to determine their origin.

This spring, Christensen plans to launch a more powerful thermal instrument on a new Mars orbiter. In 2003, twin rovers serving as “robotic field geologists” will be sent to Mars, almost certainly to one of the layered areas that have been identified.

Mars has “a lot of real estate,” said Jim Garvin, the geologist who heads Mars exploration for NASA. The new observations, he said “give us some direction . . . on where to go.”

Garvin compared the views of the layered rocks to the findings of archeologists who opened the first known tombs of the pharaohs. “These are landscapes exhumed from the Martian past,” he said.

Steve Squyres, a planetary geologist from Cornell who is heading the rover project, called the arguments that the sediments were lain down in water “pretty compelling” and worthy of a closer look. Because the layered rocks are widespread and near areas where rovers can safely land, Squyres said he was hopeful “that we’ll find some places like this where we can land and do some good exploring.”

On Earth, layered sedimentary rocks are the best place to look for fossils, the evidence of past life. The same may be true on Mars, Malin said.

Asked what the Martian surface may have been like in the past, Malin described a planet filled with lakes, some of them integrated into small seas. Because the layers are not consistent over large areas, he said, “it’s not an ocean.”

The geologists still have no idea where the water could have come from. Did it seep up from the ground? Did it rain? Did it snow? “We don’t know,” Edgett said.

Understanding the complex geology of Mars may require scientists to give up geological lessons gleaned from Earth. “We live on a planet that’s dominated by rain and water,” Christensen said. “On Mars it hasn’t rained for hundreds of millions of years. We don’t know what to expect.”