Spirit Rover Is Ready for Its Mars Close-Ups

Preparing to visit exotic locales is always a challenge.

What should you wear? What sights should you see? Without a guide, will you even know what you’re looking at?

When geologists packed up their robotic surrogate, Spirit, for its trip to Mars, they sent it off with all the gear and know-how they thought it might need.

But Mars has tricked them before.

Previous missions have brought back a wealth of information -- most of it contradictory. It’s wet, it’s dry; it’s fertile, it’s barren; the sky is blue, no, pink; it’s geologically active, it’s dead.

Spirit was scheduled to roll off its lander after midnight this morning. As the rover begins to wiggle its wheels for the first time in the fine Martian sand, the scientists will find out how well they’ve done as alien outfitters.

“Mars can absolutely fool us,” said Steve Squyres, leader of the project’s science team. “The way you design not to be fooled is to have several sensors that can look at the story from different directions, corroborate the evidence.”

Each instrument on Spirit is designed to check up on the others: nine eyes with color, 3-D, X-ray and infrared vision; a long arm (with fingers) to reach out and touch things; a microscope; two particle detectors; and a diamond grinding tool that sharpens itself like shark’s teeth (and even cleans up after itself).

Of course, there are two parts to touring: accurate observations (did you bring your glasses?) and interpretation (what is that thing, anyway?).

While today Mars is clearly “a miserable place,” Squyres said, it has many geological features that suggest a more interesting (warmer and wetter) past. But the evidence so far has been ambiguous and confusing.

The job of Spirit and its twin, Opportunity, which is scheduled to land on Mars Jan. 24, will be to collect enough data to help set the story straight.

Spirit has already been busy scoping out the terrain.

The rover’s panoramic camera (Pancam) has 20-20 vision, and it sees better than humans in 3-D.

Human stereo vision depends on the separation between our two eyes, which see slightly different views.

Pancam’s eyes, however, are wider apart, allowing it to see in depth to greater distance.

Another remote sensor, the Mini-Thermal Emission Spectrometer (Mini-TES) has been checking out the scene in infrared -- a band of the electromagnetic spectrum that penetrates surface dust and detects the presence of minerals.

Mini-TES sits on the opposite side of the camera bar from the Pancam, giving Spirit eyes in the back of its head.

To compare images of the same scene from two spectral vantage points, the rover takes one image, swivels its head around and takes another.

Pancam and Mini-TES are giving mission scientists all the information they need to pick destinations for Spirit as it heads for the rocks.

To a geologist, the mute Martian rocks speak volumes about where they’ve been and what they’ve been through. Did the minerals form in water? Are there rounded grains of sand, worn smooth by water? Do layers tell of successive deposits in the past -- perhaps in a long-standing lake?

“I’ve never met a rock that lied to me,” said James Garvin, lead scientist for the Mars exploration program at NASA headquarters. “If you read the rocks, you will not be duped.”

Close reading requires close contact, and so Spirit is built to move. Using half a dozen hazard-avoidance cameras, an internal navigation system and six wheels that are powered by independent motors, the rover is designed to maneuver itself around rocks, getting itself from place to place with minimal instructions from Earth controllers.

“The philosophy is that for anything critical, the vehicle has to be smart enough to protect itself,” said engineer Jennifer Trosper, who’s in charge of the rover’s travels on the ground.

Spirit is designed to be cautious. “We make it less cautious as we learn about driving on Mars,” Trosper explained. Once the rover proves it can be trusted to make the right decisions, mission controllers will remove some programmed protections, rather like parents extending a curfew.

After reaching its target, Spirit will extend its 3-foot titanium arm -- which just happens to be exactly the length of Squyres’ arm (“to the centimeter,” he said).

Instruments for hands-on investigations sit at the tips of its fingers.

The arm has a shoulder (with two motors; think of them as muscles); an elbow (one motor); and a wrist (two motors).

Each “finger” has a feeler that signals Spirit’s computer when contact has been made. The first task might be a bit of housekeeping -- scraping off accumulated rust and dust that camouflage the true nature of rock underneath.

A human geologist would get inside the rock by taking “a big ol’ hammer” and whacking it, Squyres said. Safety goggles are recommended.

The rover has to take a subtler approach. Spirit carries a RAT, or Rock Abrasion Tool, that can drill a 2-inch-diameter hole about the depth of a tooth filling. Tiny brushes clear away the debris.

The diamonds that serve as RAT’s teeth, however, eventually wear out -- and there’s no one on Mars to replace them.

The solution was to embed the diamonds in material that itself wears away, continually exposing fresh diamonds.

After clearing away the surface crud, Spirit can look at the rock close up with the combination magnifier/camera that sits on the end of its second “finger.”

Like a geologist’s hand lens, it can reveal the texture of the rock at very fine scale. Layers, rounded grains, and the way grains are sorted by size all hold clues to the environmental conditions that went into creating it.

To look deeper, Spirit will use its Alpha Particle X-ray Spectrometer (APXS). The device contains a nugget of radioactive curium, which shoots the rock with subatomic bullets known as alpha particles (pairs of protons and neutrons).

If the alpha particles bounce back fast, then it means they hit a fairly heavy atom (think bowling ball); if the particles come back slowly, they hit a lightweight atom (think pingpong ball).

Since the mass of an atomic nucleus reveals its character, the APXS can identify elements, revealing whether a rock contains, for example, carbon or oxygen and, if so, how much.

The curium also emits X-rays, which kick atoms into an excited state.

When the atoms fall back to their normal state, they emit light of very specific frequencies -- fingerprints of elements. The X-rays are used for detecting heavier elements such as magnesium.

APXS can’t detect hydrogen, meaning it can’t detect water, which is made up of hydrogen and oxygen -- H2O.

But Mini-TES can, and so each makes up for the other’s blind spots.

Finally, each Mars rover carries a sophisticated instrument, known as a Mossbauer spectrometer, that can look directly into the nucleus of an iron atom to distinguish among iron-bearing minerals.

The spectrometer uses gamma rays from radioactive cobalt to pump energy into the iron nucleus; the iron then spits out the energy in a very specific gamma-ray spectrum -- a nuclear fingerprint.

The presence of other elements nearby subtly alters that fingerprint, however.

The Mossbauer detects the change by moving the cobalt back and forth 25 times a second, varying the wavelengths, and therefore the energy, of the gamma rays.

Exactly like tuning a radio to different frequencies, the Mossbauer “tunes” the gamma rays so that they can “hear” one nuclear configuration after another.

Each configuration means that a different set of molecules is in the neighborhood. Different neighbors mean different minerals.

Spirit carries other, less exotic equipment -- magnets, for example, that collect magnetic dust to be analyzed by the APXS and the Mossbauer.

“When we pick a rock we think is a particularly tasty target,” Squyres said, “we’re going to hit it with everything we’ve got.”

Carrying all this equipment on its back, Spirit has a distinct advantage over human geologists, who must take rocks back to the lab for analysis.

Plus, the rover has a large team of colleagues to interpret its findings.

“In the field, you usually go with one field assistant, who might be an undergraduate,” said Joy Crisp, project scientist. “Here you’ve got 50 top planetary scientists working together. If you don’t know what something is, you can ask someone.”

The downside is, robot geologists are “frustratingly slow,” Squyres said.

The RAT takes two hours to grind 5 millimeters into rock. The APXS and Mossbauer can take 10 to 12 hours to get a clear reading in Mars’ highly radioactive environment.

The rover moves at the speed of a giant tortoise, has limited energy and is, after all, a geologist of little brain itself -- meaning it has to await instructions from Earth, which arrive only once a day.

During a field test with a similar rover named Fido, Squyres used a stopwatch to compare a group of human geologists with the robot. It took the humans roughly 45 seconds to find a rock, walk over to it, pick it up, break it open, look inside.

“For Spirit, that takes a day,” he said.