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<i>Spirit</i> Enters Rocky Terrain on Mars - 2004-02-27

The U.S. Mars rover Spirit has entered the rockiest terrain it has encountered since arriving in January, as it heads for a crater to search for signs that water once flowed on the red planet. A mission scientist says he is confident the water question will be answered in about a month, when Spirit and its twin, Opportunity, have gathered more data.

Spirit continues to roll slowly toward a crater nicknamed Bonneville, as scientists stop it to analyze rocks and soil along the way. The goal is to understand the upper crust of Mars and how water might have influenced it if it ever existed in large amounts.

On its way to the crater, the six-wheeled vehicle has run into bigger rocks than it found nearer its landing site. Scientists say it is material that was thrown out of the shallow crater by whatever smashed into it.

Spirit's computer is programmed so the rover can navigate itself around obstacles without commands from ground control. But mission manager Jennifer Trosper says that because the obstacles are getting bigger, engineers are testing new software that will make its journey easier.

"It's becoming more and more challenging to drive in this terrain, so one of the things we have on our plate [have planned] in the next month is we're actually going to upload new flight software to both Spirit and Opportunity," he said. "We want to be more robust to the types of terrains we're seeing here in these images. We also want to speed up the autonomous navigation algorithm so we can drive further in the time we have each day."

The Opportunity rover on the other side of Mars remains at an area of exposed bedrock, taking images and using its instruments to measure structure and mineral content. Mission geologists want to understand the environment in which each layer of the rock was deposited. Is it made up of sediments deposited in water, are they compressed volcanic ash, or are they an accumulation of windswept material?

Washington University geologist Ray Arvidson says the rovers are still acquiring data, but adds that by the conclusions of their three-month missions in April, the information should reveal whether liquid water did or did not flow in large amounts on Mars ages ago.

"I wouldn't be surprised but that we will be able to say a lot about the role of water or not in terms of these two particular sites," he said. "Water is the elixir of life and if we come up with the conclusion that water has been involved in the surface or subsurface at some time in the past, then I think the probability that prebiotic systems could have been generated and life could have gotten started goes way up."

In the meantime, the scientists released images of a martian sunset that looks very Earthlike. When displayed in quick sequence, they show the sun descending from a blue sky into a haze of reddish dust that could be mistaken for large city smog. The pictures are not unprecedented. The U.S. Viking landers in the 1970s and the Pathfinder rover in 1997 also took pictures of sunsets and sunrises on the red planet. But the Cornell University scientist who developed the camera that took the latest images, Jim Bell, says they are special nevertheless.

"You're observing the sun setting on another planet," he said. "I mean, how often do you get to do that, right? It's important not to forget that what we're doing does have special inspirational moments like this."