BOOK OF STONE
You're standing on a history book - a very large history book. The geologic history of the Earth is written in the rocks and soil under your feet. But it's not easy to decipher. Early chapters have been erased forever by erosion. A churning molten core, massive plate tectonics, and scouring winds and water have recycled and eroded Earth's rocks. Geologists must piece together the truth from a very fragmentary record.
Other worlds on this side of the asteroid belt also wear their stories in stone. Mars tantalizes scientists with its dramatic features - huge volcanoes, massive canyons, and complex networks of ancient river valleys. These landforms are monuments to a planet that was once very active. Today, the surface of Mars appears barren, dry, cold, and lifeless. Why such a dramatic difference? The answer lies in the planet's dust, rocks, and soil.
When geologists want to "read" a rock here on Earth, the usual procedure is to look at its surroundings and its outer surface to gather information about the forces that created its current condition. Was it carried by water? Born from a volcano? Eroded by wind? Geologists look at the rock's texture, size and color. They crack it open to understand how it was formed. What is its mineral content? Is it a conglomerate of rock fragments? Was it changed by heat? Does it have layers? They also look at the soil where the rock was found. Are soil grains uniform or do they have irregular sizes and shapes? Depending on these and other factors, a picture begins to form about the rock's age, its surroundings, and its history.
Unfortunately, geologists cannot yet ply their trade in person on the surface of Mars. For now, robots must do the job. One of the main objectives of the Mars Exploration Rover mission is to study a variety of rocks and soils to determine what role water has played in the history of the Martian surface. When scientists discuss the prospect of finding evidence for past water on Mars, they use phases like "hematite signature" and "hydrothermal activity." Hematite is an iron-based mineral (iron oxide) that can form as a result of "hydro" (water) and "thermal" (heat) processes. The presence of hematite on Earth usually indicates a history of water activity. But this is not always the case. Should the rover land in a hematite-rich region of Mars, scientists will test several hypotheses to learn how the mineral formed. In the process, they may find minerals that formed in water.
The Mars Exploration Rovers will land at two locations on Mars where water may have existed many years ago. The rovers' science instruments will read the geologic record preserved in the rocks at the two sites. Pancam and Mini-TES panoramas will help scientists choose interesting rocks. The rovers' spectrometers, rock abrasion tool and microscopic imager will look at the selected rocks in detail, provide spectra of their mineral content, grind into their surfaces, and get close up views of their interiors.
Scientists will piece together the information the two rovers gather to determine, not only if water has been present on Mars, but if conditions could have been suitable for life. All this and more from a history book carved in stone.
Web content editor/writer: Pamela R. Smith
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