Destination Mars (21 page)

O
n sol 159, the indefatigable rover Spirit reached its first stop at the Columbia Hills. It had been dawdling, pursuing its scientific endeavors, at Lahonten Crater since sol 118, driving around the rim of the two-hundred-foot depression. Then the long drive to the hills began.

At the base of the hills, it spent a full twenty-three sols studying a feature known as Hank's Hollow, and in particular an odd-looking rock named Pot of Gold (there was no lack of imagination within the MER team). Lo and behold, there be hematite in these hills—Spirit was catching up with the discoveries of its precocious twin, Opportunity. The rock was described as looking “as if somebody took a potato and stuck toothpicks in it, then put jelly beans on the ends of the toothpicks”; a colorful way to describe the oddly shaped, softball-sized rock. The process of formation was thought to be water based, especially because hematite is usually found in the presence of water. But there are chemical processes that could result in such a feature, so it was studied exhaustively.

After investigating with its “sniffer,” the rover repositioned itself (which took several sols, due to the slippery and treacherous nature of the surrounding soil) and ground away at another side of the rock with the RAT. Whatever formed this rock took a long time and was not a mild process. It was harshly eroded and knobby, and the nodules on the rock appeared to be cousins to the “blueberries” found by Opportunity, half a planet away.

Spirit left Pot of Gold to investigate more strange-looking rocks nearby. Dubbed Cobra Heads, these rocks, as did Pot of Gold, appeared to have come down from higher up in the Columbia Hills. The Cobra Heads were probably the cores of more normal-looking rocks that were left behind when the softer surrounding layers wore away to leave the harder interior behind, silently hissing at Spirit.

At this point, while still very capable, Spirit's spirit was being dampened by some problems. The mechanical arm was suffering from a bit of dysfunction in one of the motorized joints. The radio was having issues, making the reception of commands sent from Earth difficult. And the front right wheel was draining far more electrical current than the other five, and this drain was increasing. It was an indication that the gearing that drove that wheel was failing, probably due to sand, dust, and grit having crept inside. To make matters worse, the season was advancing and Spirit was receiving less sunlight on its solar panels every day.

Still, the rover continued its labors, taking a northerly course along the base of the hills, investigating as many rocks as it could along the way. Then, on sol 239, the rover powered down for solar conjunction, when Mars is on the far side of the sun from the Earth and out of communication with JPL.

When we last left Opportunity, it was embarking upon the long and lonely journey to Endurance Crater. On April 30, 2004, the mammoth feature loomed into view. About 430 feet across, Endurance Crater is named after the ship captained by Sir Ernest Shackleton on his epic voyage to Antarctica. It was a fitting name for a landmark so prominent in Opportunity's life.

The rover paused at the lip of the crater, taking its time to survey the sixty-foot-deep interior. As with most impact craters, Endurance ripped through the surface of the planet, exposing the strata below. Finding a suitable point of entry, Opportunity, shaking its metal arm in the Great Galactic Ghoul's odious face, took the plunge and began the risky descent into the crater. The
point of entry was named Karatepe (“Black Hill” in Turkish), and the rover took a tentative drive inside the crater rim, then stopped and backed out, just to make sure that it could. It was a bit like watching Neil Armstrong on that July night in 1969, coming down the ladder of the Lunar Module, then before setting foot on the moon, hoisting himself back up the rungs just to be sure that
he
could.

Nobody wanted Endurance Crater to be the final resting place of Opportunity, though everyone involved knew that it might be. As it turned out, the rover spent the next
six months
driving around Endurance Crater. The first stop was a patch of exposed bedrock strata. Opportunity got up close and personal with the outcrop and sampled each layer of the strata as carefully as possible. It noted that both the texture and the chemistry of the rocks varied with depth, with the lower layers being the oldest, just as on Earth. And both magnesium and sulfur declined in abundance as the rover's sniffer went from the upper (younger) to the lower (older) rocks, once again confirming the presence of (and alteration by) water in the past.

Moving on, more “blueberries” were seen in the rocks and scattered about the crater itself. Soon the same solar conjunction that idled Spirit forced Opportunity to cease operations for two weeks as the two rovers waited out the silence from Earth.

As Mars moved back within range of the ground controllers, Opportunity moved to a rock unlike anything seen in the Meridiani Planum area. Dubbed Wopmay (after a semifamous Canadian bush pilot), its lumpy, serrated surface promised more signs of alteration by water. More “blueberries” were found here as well, and the sightings of these was becoming almost boring…almost. Again, signs of a watery past.

About this time you might well be wondering just how much evidence of water in Mars's past a planetary scientist might need. It's a good question. But with such an arid planet meeting virtually every spacecraft sent there, and the promise of life, past or
present, dangling on this finding, there could be no such thing as too much evidence. Not yet anyway.

Tellingly, the investigation of this rock corresponded with the publication in a scientific journal of the results of the MER missions' efforts to find evidence of a watery past on Mars. The paper included the efforts of 122 authors and was confidently published in
Science
, perhaps the most important journal appropriate for this kind of news. This made it official: there has been large amounts of water on the Red Planet, and the evidence would just keep piling up. Besides the “blueberries” and various chemical residues, there were cavities, the oddly named vugs, in many of the rocks investigated that were indicative of crystals that had been dissolved over time by water as the rocks lay immersed. This finding, wondrous in the extreme, told of not just large amounts of H2O, but also that it had existed as a liquid on the surface of the planet for a long time in the past. And this indicated a thicker, warmer atmosphere way back when.

If there was a downside, it was that this water would have been salty and acidic and not overly friendly to life. But life finds a way, as it has in so many hostile environments on our own planet, so this was far from a deal breaker.

Returning to Spirit and its numbing slog across the Gusev region, the rover had found something interesting (well, it was
all
interesting, but this was a major find). The mineral in question was goethite, kin to the jarosite found earlier by Opportunity, and it was another sure indicator of water sometime in the past. The beauty of this mineral is that, unlike hematite, which
usually
forms in a watery environment, goethite forms
only
within such an environment. Anyone sweating out the declarations in the
Science
article could take a deep, relieved breath.

Making spirits brighter, to coin a phrase, the worrisome friction buildup in the front right wheel was diminishing. Nobody could be sure why without a mechanic's house call to Mars, but the fact that controllers had been “babying” that wheel may have
helped. All they knew for sure was that it was drawing less current, and that was a good sign of mechanical health.

Spirit now ascended a formation known as Husband Hill (named after the NASA astronaut who died in the shuttle
Columbia's
demise) in an effort to ascertain how high the water might have once stood. The hope was that it was not merely an underground store but might have pooled on the surface for some length of time, as it appeared to have done at the Opportunity site. Confirmation was the name of the game.

Then Opportunity, never content to allow Spirit to bask in the limelight for long, found something wonderful.

Ascending out of Endurance Crater, the rover had spied its own heat shield from its fiery descent onto Mars. Scientists wanted to examine the structure to see how it had been affected by its hot journey through the Martian atmosphere, and the results were interesting, if not remarkable. Nearby was an interesting rock, dubbed, appropriately enough, Heat Shield Rock. As the rover neared this stone, it began to look eerily familiar to some on the ground, and very unlike the others they had been investigating. Soon, it was confirmed. Opportunity had found the very first meteor found on another planet. Where it came from (besides space) and when it arrived would remain a mystery, but finding it was excitement enough. And it was an iron-rich meteorite, not the more common “stoney”-type. Of course, meteorites are found on Earth, so the rock itself was not the real news. What it would reveal about the area on which it sat was the interesting part. It could help to answer the question about whether or not Meridiani Planum was gradually eroding away as so much of Mars is, or if it was still being built up in geological terms.

Soon, Opportunity moved on. The region it was crossing was sufficiently flat that it allowed controllers to test more autonomous driving than before, depending on the rover's onboard computer to avoid hazards and obstacles. So the first part of each drive was based on a course set by ground controllers,
then switched over to the onboard navigation system. This was a good test of JPL's software, and the rover passed with flying colors. Up to a quarter mile was covered in this mode, a new record.

Months later, in June 2005, Opportunity had a near-death experience. It had gotten bogged down in a small sand dune, and it struggled for almost five weeks before freeing itself. Had the arm been able, it might have wiped a bit of sweat from its metallic brow, but Opportunity instead took a time-out to access its health before carrying on. At the same time, JPL wanted to know why Opportunity had gotten stuck in an area that looked so much like regions the rover had crossed with ease before.

Far away, in December 2005, Spirit spent some time staying up at night to observe a meteor shower. Mars, like Earth, passes through swarms of cometary debris every year. The comet in question was the famed Halley's Comet, and the resulting show did not disappoint. It was what researchers call “bonus science,” an unplanned addition to the rovers' busy schedules.

By mid-2006, Spirit had to find a place to spend the harsh Martian winter once again. The fact that both machines had performed far beyond expectations, and had vastly exceeded their warranties, was remarkable enough. But nobody wanted to lose one to the winter cold for lack of planning.

After descending from Husband Hill and investigating a formation called Home Plate, Spirit parked itself on a north-facing slope to allow for maximum exposure of its solar panels through the winter months. Spirit would need all the power it could get to keep warm through the long cold period. An added drama was that the front right wheel, the previous source of concern, had finally given up and was no longer functioning. From now on, Spirit would be dragging one foot as it ambled across Mars.

Opportunity had just wrapped up four months at a 1,000-foot wide crater called Erebus, after the volcano in the Antarctic.
¹
It had found thin, rippled rock indicative of flowing water—another important discovery. Sitting water was turning out to not be unique in Mars's ancient past, but evidence for wind-blown water was still being sought to confirm interactions between weather and standing water.

Soon Opportunity continued on its trek, heading off on a long drive to the largest and most promising crater yet, the half-mile-wide Victoria Crater, named after one of Ferdinand Magellan's ships. Over two hundred feet deep, Victoria had exposed bedrock layers over 130 feet high, and promised a treasure trove of new information. The larger and deeper the crater, the more of Mars's geological past would be revealed.