Nasa's Spirit rover signs off on Mars

One of the more interesting phenomenoms encountered on Mars by Spirit was the existance of mini dust storms called "dust devils". Here is a series of images of one dust devil captured in 2007.

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Bedrock shown in this image from 2004 reveals a complex geological history. Some of the rocks show signs of water erosion.

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In 2005, Spirit sent back this image of an area that contained sulfur and possibly a trace of water. It's most likely a volcanic deposit formed around gas vents.

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A few months after it landed, Spirit's left front tyre began showing a problem by using much more energy than the others.

Here, Jet Propulsion Laboratory (JPL) engineers Eric Aguilar (left) and Joe Melko work in a sandbox to find a way around the problem. The wheel eventually died in 2006 but Nasa scientists were able to keep the rover rolling on five wheels by driving it backwards and devising easier ways to turn.

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On a positive note, the dead wheel dug up Martian soil that in turn led to Spirit's most impressive discovery — a patch of nearly pure silica. This was most likely caused by hot springs or steam vents.

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Five years after this image was taken by Spirit in 2005, Nasa scientists concluded that this area showed a past that was wet and non-acidic and could potentially sustain life as we know it.

The rocks were identified as magnesium iron carbonate with a concentration of carbonate 10 times that ever seen on Mars. According to the space agency, carbonates originate in wet, near-neutral conditions, but dissolve in acid.

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This artist's impression shows what Spirit would look like on Mars. Nasa, meanwhile, has compiled an affectionate Curriculum Vitae of the Spirit rover.

The Mars Opportunity rover, which landed on 25 January, 2004, continues to roam the surface of the red planet. 

For more on this ZDNet UK-selected story, see What rover Spirit discovered on Mars (photos) on ZDNet.com.

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