When Marjorie A. Chan saw the first photographs of little nodules on the Red Planet, she thought, "Oh, my gosh, there's been groundwater flow on Mars."
Sitting in her office in the University of Utah's William Browning Building, she cupped a double handful of small iron spheres called Moqui marbles. The "marbles" came from southern Utah — but they looked so much like the nodules in the Mars rover photos that they almost could have been collected on the desolate plains of Meridiani Planum.
Moqui marbles and the Mars nodules are similar because they probably came about in much the same way, according to research by Chan and colleagues. And since they know how the Utah concretions formed, that is a strong tip-off about how those of Mars originated.
Most likely, it means Mars also hosted liquid water at one time in its long history. That fact could be crucial to the search for life elsewhere in the solar system, as life as we know it depends on water.
Chan, a professor and the chairwoman of the U. Department of Geology and Geophysics, is the lead author of an article just published in Nature Magazine, "A possible terrestrial analogue for hematite concretions on Mars."
In addition, the Utah spheres might point to a good place to search for Martian fossils, she believes. Moqui marbles probably precipitated more quickly because of the presence of bacteria in the porous Navajo sandstone. If a future Mars sampler probe collects nodules and returns them to Earth, they might include microscopic fossils.
Hematite is a form of iron, and the Moqui marbles are largely iron, sometimes with sand remaining in the center.
Rover scientists call the Martian nodules "blueberries" because they are slightly grayer than the orange rock and sand of that region on Mars. When the team used the rover's spectrometer to analyze a group of blueberries, they discovered they were made of hematite, an iron ore.
"Hematite is one of the few minerals on Mars that are directly linked to water processes," Chan said.
For about eight years, she has been looking for the reason that southern Utah sandstones are of different colors, and trying to understand how the colors relate to Moqui marbles found there. Many of Utah's iron spheres, which can range from tiny to several inches across, are from areas where the sandstone is white.
"We realized that a lot of these concretions formed from the interactions of different kinds of water," she said.
Navajo sandstone throughout southern Utah is the petrified remnant of deserts dating to the Jurassic period, about 200 million years ago. Many of the sandstone's individual sand grains were coated with a thin film of hematite, she said.
In Australia some modern sand dune fields are orangish because of hematite on the sand grains.
After the Utah sand dunes were petrified, turning to sandstone, water moved through the orange layers. Hydrocarbons carried in groundwater and bleached the sandstone, stripping off the hematite.
Sandstone in the southern part of the state often shows red and white stripes, with the white being where water seeped through and bleached the rock. The red is where more hematite remains. (A brochure on the subject, written by Chan and one of the co-authors of the Nature article, is posted on the Internet at geology.utah.gov/online/pdf/pi-77.pdf.)
When fluid carrying the hematite oxidized, the iron precipitated out. The precipitate is in the form of balls — Moqui marbles.
"It's essentially a chemical reaction front" that caused the bleaching and precipitation, she said.
Why are the marbles that shape? Because of any pattern in nature, a ball requires the minimum energy to form. It's why we don't have square hail.
A year ago, Chan and another geologist were in the field examining the Navajo sandstone. Before the landers made their discoveries, he contacted her, saying, "I think the iron concretions you've been studying in southern Utah might relate to how you get hematite on Mars," she recalled.
Last fall, she traveled to Spain and met with her collaborator, and "we worked out a lot of the similarities about some of the hematite regions on Mars and southern Utah," she said. Sandstone bleaching patterns in this state looked as if they might "match some patterns on Mars."
When Opportunity landed and took its photos, they realized the similarities were real. "It took the MER (Mars Exploration Rover) team quite a while before they came to the same conclusion that we did."
Utah's concretions are "a little bit more variable" than the blueberry nodules. "They may not be as purely crystalline as the ones on Mars," she added, because Moqui marbles have other iron oxides as well as hematite.
"There are probably a lot of differences, like where did the iron come from?" Chan said. On Earth the host rock is quartz-rich sandstone. On Mars some of the host rock may be basaltic, which comes from lava.
"The main thing is, despite those differences, we know that when you see those concretions it means, No. 1, the rock was porus. Fluids had to move through."
The process needs groundwater flow. And "it requires the right kind of chemistry."
Chan thinks this aspect of Utah geology will be "one of the premier analogs" for interpreting and understanding certain features on Mars.
Other authors of the study are graduate student Brenda Beitler and emeritus professor William T. Parry, both from the University of Utah; Jens Ormo of the Instituto Nacional de Tecnica Aerospacial in Madrid, Spain, and Goro Komatsu of the International Research School of Planetary Sciences in Pescara, Italy.
E-mail: bau@desnews.com