For now, researchers are examining images recently obtained by the Mars Orbiter Camera (MOC) aboard NASA's Mars Global Surveyor spacecraft. The black-and-white pictures show layered rock formations on the Red Planet that may be signs of ancient lakes.
The colorized versions, including those on this page, are an approximation of what a human would see on Mars, say researchers at Malin Space Science Systems who created the images.
The researchers used other color images obtained with a different camera aboard the spacecraft, as well as MOC pictures and images from the Viking Orbiter taken in the 1970s, then synthesized all three sources to represent "a crude approximation of Martian color."
Layers in West Arabia Terra Crater
| Windblown Sand |
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Dark areas are windblown sand, enhancing the appearance of layers.
Click to enlarge
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In one area imaged by Global Surveyor, hundreds of layers of similar thickness, texture and pattern have been exposed by erosion in a 40-mile- (64-kilometer-) wide impact crater in western Arabia Terra. These layers provide a record of repeated, episodic changes that took place at some time far in the Mars' past.
Layers toward the center of the crater are nearly horizontal, but those closer to or draping over the crater walls are tilted toward the basin center.
These relationships suggest that the sediments that created these layers were deposited from above --- perhaps by settling out of the Martian atmosphere, or perhaps by settling out of water that might have occupied this crater as a lake, said Michael Malin and Kenneth Edgett of Malin Space Science Systems.
"We have only solved one little piece of a tremendous puzzle," Malin said. "There is no illustration on the box to show us what it is supposed to look like when it is completed and we are sure most of the pieces are missing."
How the layers might have formed
| Two Options |
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Graphic explains two ways the layering might have formed. Click to enlarge
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A cross-section of Mars shows the upper few miles (kilometers) of the planet's crust and illustrates the processes that might have contributed to the formation of recently imaged sedimentary layers, Malin says.
Two basic processes are portrayed: deposition of sediment as dust settling out of the atmosphere, and deposition in bodies of water such as crater lakes and shallow seas.
The chief source for sediment in both cases may be a combination of materials produced by explosive volcanism and meteorite impact, as well as weathering and erosion, researchers said.
Malin and Kenneth Edgett have suggested that the some of the layers may have formed underwater in lakes or perhaps shallow seas inside craters.
If the sediment fell from the air, then some recurring phenomenon would have had to create thin layers of regular thickness and properties -- the type of deposition that occurs in bodies of water.
Malin and Edgett explained how deposition from the air might have occurred. The atmosphere's pressure might have varied on a regular basis from something that is hundreds of times thicker than it is at present to something that is perhaps only tens of times (or less) thicker than it is today. As the atmospheric pressure went up, it could have carried more dust to be deposited; as it went down, there would have been less.
It is also possible, the researchers say, that the layers were created by a combination of deposition from the air and from water.
"Ultimately, geologists will have to go to Mars," Malin said, "to investigate the changes in ancient Martian environments recorded in these rocks."
Jack Farmer, director of the astrobiology program at Arizona State University, said standing water is the most likely explanation for the layering.
"This truly is exciting stuff," Farmer told SPACE.com. "If true, it indicates that water-lain sediments could be much more widespread than we thought previously."
But Farmer agreed that only surface testing would provide convincing evidence for how the layers formed. He added that the Mars Global Surveyor mission has helped researchers who would decide where to look for signs of life on Mars.
"But MGS has also continued to show us that we still have a lot to learn about Mars," Farmer said. "My prediction is that there will be many more interesting surprises before we are in a position to actually try to answer the question of Martian life."
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