Mars rover spies pot of gold

Tantalising new images are cascading back from NASA's Mars rovers now that they have reached their long-awaited geological sites.

Spirit is now at the edge of the Columbia Hills facing what appears to be an easily-accessible hilltop straight ahead. The hilltop should offer vistas of the surrounding plain that is believed to be an ancient lakebed.

The headland also appears to have an abundance of geologically interesting rocks and formations. Most startlingly, there are rounded pebbles reminiscent of the ubiquitous "blueberries" seen at Opportunity's landing site, Meridiani Planum, halfway around the red planet, says geologist Larry Soderblom, of the US Geological Survey, and a member of the rover science team.

As scientists watched the latest images arrive from Spirit's Gusev crater site at the base of the hills, their reaction was: "Are you sure that's not Meridiani?"

Though similar in size, the spheres seem to be more varied in shape, ranging from spherical to egg-shaped. And, as at Meridiani Planum, they seem to be weathering out of layered rocks.

Here, some of those rocks look like "a loaf of bread that's under a state of decay," with thin crusts remaining as the interior weathers out, Soderblom said on Tuesday at NASA's Jet Propulsion Laboratory.

Geological contacts

One of these rocks is so varied and different from any seen before at Meridiani Planum, that it prompted Soderblom to call it "the pot of gold, the prize at the end of the rainbow".

So far, nobody has an explanation for the remarkably resistant crusts seen, he says. But "it's hard to imagine that water wasn't involved", he adds.

Meanwhile, Opportunity has begun its plunge into the interior of Endurance crater, perhaps 20 metres deep and 190 wide. Now about five metres down, it sits near the first of several geological contacts - boundaries where there are clear changes in the composition of the rock - visible in the heavily layered bedrock.

"In geology, contacts are always going to tell you something about a change in conditions," said geologist Scott McLennan of the science team. And this contact represents the transition into whatever preceded the formations Opportunity studied earlier in a tiny crater called Eagle, which provided definitive evidence of liquid water in the past.

Front wheel

Now the team is hoping to find out how long those watery conditions lasted - was the preceding epoch drier, or even wetter? The full suite of spectrometers in its arsenal will first be deployed on the rock just above the contact, and then in a few days do the same to the rock below to study the differences.

Meanwhile, Spirit has shown increasing resistance in its left front wheel, seriously affecting its performance. Mission manager Mark Adler says the wheel is likely to fail altogether in another 100 metres or so. The team is considering just operating with the other five wheels, except in rare cases where they need the extra power to climb a slope, for example.

But Adler says the team remains optimistic that the twin rovers, already two months past their warranty expiration, could keep going strong. And, Soderblom adds, if they can hunker down and survive until January, the arrival of spring on Mars should greatly increase the rovers' power supplies and perhaps give them a second wind.

If you would like to reuse any content from New Scientist, either in print or online, please contact the syndication department first for permission. New Scientist does not own rights to photos, but there are a variety of licensing options available for use of articles and graphics we own the copyright to.