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Memory problems, a dead wheel, dust storms, and three bitter Martian winters have barely slowed the Spirit rover, which has been scooting around Mars since January 2004. But in May, another obstacle stopped it in its tracks: a mound of powdery soil that ensnared the golfcart-size robot like quicksand.

Spirit’s wheels churn into deep, powdery soil shortly before the rover became stuck in this wide-angle view. [NASA/JPL]

Spirit was circling around a small plateau named Home Plate when it bogged down in the deep patch of soil, which is about the same consistency as flour. The rover’s right front wheel died years ago, so Spirit now uses its other five wheels to drive backwards. The dead wheel was complicating efforts to shake Spirit free of the soil.

Home Plate, which is named for its appearance in pictures from orbit, may be the remnant of an ancient volcanic explosion. After parking near the edge of Home Plate during the last Mars winter, Spirit began studying the feature again late last year. It tried to scale one corner of Home Plate in March, but had to abandon the effort because it kept slipping backward in the loose soil.

Even if engineers cannot extract Spirit from the sand, the rover can continue to study the rocks and soil around it. It was designed for a three-month mission, but has survived for five and a half years.