Mars Rover Digs Trench to Search for Evidence of Water
David McAlary
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http://language.chinadaily.com.cn/dialogue/voa/normal/2004/02/0217a.rm
One of the U.S. Mars rovers has spun a wheel to dig a shallow trench in the sand in the continuing search for evidence that water once flowed on the red planet. The second rover is in the midst a long trek（艰苦跋涉）to a nearby crater（火山口）that will take several days.
The Opportunity rover hugged the slope of the crater it landed in three weeks ago, as mission controllers in California commanded it to rotate its right front wheel back and forth. The result is a 50 centimeter long trench about nine centimeters deep.
"We took a patient, gentle approach to digging," space agency engineer Jeffrey Biesiadecki. "No single maneuver we did actually moves all that much material. Rather, it's a gradual process that digs deeper and deeper the longer we let it run."
The rover is digging in an area rich in the mineral hematite（赤铁矿）, which can form in water. Mission scientists want to see how deep the hematite goes and are analyzing it with rover geology instruments to determine whether it actually formed in water. Evidence of the liquid would suggest Mars was once hospitable to life.
One of the researchers, Rob Sullivan of Cornell University, says the science team is intrigued by patches of sand at the bottom of the trench that are brighter than that on the surrounding surface.
"It could be in fact that we've discovered something that is intrinsically different down on the floor of this trench than what we've seen so far on the surface. It's also possible that there may be some increased fine particles down where the trench floor is and they have been very carefully molded under the weight of the wheels. So there could be a reflection effect."
On the other side of Mars, the twin rover Spirit is studying soil and rocks as it gradually makes it way over several days to a crater nicknamed Bonneville, about 240 meters away.
The six-wheeled vehicle has traveled 108 meters since it arrived 45 days ago, a Mars distance record. It has exceeded the amount of territory covered by the Sojourner rover mission in 1997 by about six meters.
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