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Soundings: Are the data worth the risk?

Alan Stahler

Diamonds only form deep in the Earth; opals precipitate only in water; aluminum oxide becomes a rich red ruby when mixed with a few atoms of chromium; replace chromium with a few atoms of iron and titanium and it becomes a deep blue sapphire.

Different minerals form in different ways, from different atoms, in different surroundings. The minerals in rocks thus tell us what the environment was like when the rocks formed. The history of a planet can be read in its rocks.

Bouncing off the only good-sized rock anywhere in sight, the Mars rover Opportunity last January scored an incredibly lucky “300-million-mile hole-in-one,” ending up at the bottom of a crater.

Slamming into the surface at tens of thousands of miles an hour, the meteor that excavated Eagle crater penetrated Mars’ veneer of sand and dust and loose rock to reveal something never before seen by human eyes: Martian bedrock, part of the solid body of the planet.

It was from this bedrock that Opportunity – our robotic hands and eyes – extracted the data that told of ancient water on Mars.

Opportunity has now moved on, and sits today on the rim of yet another crater. Endurance crater is deeper than Eagle; deeper rocks are generally older, and should bear stories that go further back in Martian history.

Should we send Opportunity into Endurance crater to read those stories?

After it had studied Eagle crater for some months, Opportunity was instructed to climb out.

It didn’t make it on the first try.

The twin Mars rovers were designed by 20 engineers at NASA’s Jet Propulsion Lab in Pasadena, led by Randell Lindemann. I asked Lindemann what went wrong on that first try.

Any two of Opportunity’s six-wheel drive motors could, if necessary, lift the rover straight up. Power was not the problem.

Much of Mars is covered with dust – a slippery surface. Climbers strap crampons – metal spikes – to their boots to climb on ice or steep snow. Crampons bite into the ice more aggressively than rubber boot lugs.

Unfortunately, they also tend to snare your pants, your partner’s parka – whatever they happen to brush against.

Opportunity’s wheels bear cleats to give them more grip in the slippery dust. The engineers knew that, as Opportunity drove off the lander that had carried it in its incandescent fall through the Martian atmosphere, she would also likely drive over the deflated air bags that had cushioned the landing. To avoid snagging an air bag and wrapping it around a wheel – ending the mission before it had begun – the engineers made the cleat pattern less aggressive than they might have.

Images of Opportunity’s tracks, though, show no sign that lack of traction was a problem.

According to Lindemann, there probably was slip, but not where the metal met the sand. Rather, slip likely occurred in layers of sand and dust below the surface – rather as if Opportunity were trying to walk up a “down” escalator.

Opportunity eventually escaped Eagle crater by traversing at an angle up another part of the crater wall.

Now Opportunity sits at the rim of Endurance crater. The view from the rim, down into the crater, is intriguing.

But while Eagle crater was only 7 feet deep, Endurance crater is roughly 70.

Opportunity will spend the next couple of weeks exploring the region, while scientists and engineers debate – as they did in choosing landing sites before launch – whether the stories in the Endurance crater rocks might be good enough to risk ordering Opportunity into a place from which it might never escape.

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Alan Stahler trained as a biologist and is an amateur astronomer. He teaches enrichment classes for children and adults at Sierra Friends Center. His science programs can be heard at noon on alternate Tuesdays on KVMR-FM (89.5).


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