Destination Mars (12 page)

T
he rock smelled. Of course, it was supposed to smell. As she took repeated whiffs of it, there was little to compare to. Sojourner knew only
this
rock…it was the first one she had smelled since arriving on Mars just under three days ago.

It didn't smell in the traditional sense that humans or animals would experience. Sojourner's “nose” was a highly sophisticated device, a marvel of robust yet lightweight and compact engineering called an Alpha Proton X-ray Spectrometer (APXS). This little machine, just a fraction of Sojourner's twenty-three-pound overall weight, was designed to analyze the chemical composition of Martian rocks using protons it emitted to excite the elements making up the rock in question. Using this, Sojourner could smell just five things: sodium, magnesium, silicon, aluminum, and sulfur. But her designers had decided that this would be enough, and it was. For, while it could not distinguish between a Bolognese sauce and raw onions, it would be able to identify the basic makeup of a rock. And that was far more valuable on the surface of Mars than an epicurean snout.

It was not a fast process, however. Sniffing this first rock, affectionately named “Barnacle Bill” by JPL scientists after its surface, which appeared to be encrusted with the fishy crustaceans, took over ten hours to complete. But Sojourner was patient; she had already endured eight months in the cold darkness of space and a rough-and-tumble arrival on Mars. Ten hours at one rock—
an interesting one to boot—was little in the grand scheme of things. So she took her time.

Just under three days, or
sols
, previous (a sol is a Martian day, just a bit longer than an Earth day at 24 hours and 39.5 minutes), Sojourner had arrived on Mars in dramatic fashion. After her long cruise through the interplanetary void, she had skipped entering Mars orbit as had her predecessors, Vikings 1 and 2, and shot straight into the Martian atmosphere. It was all part of NASA's “faster, better, cheaper” approach to unmanned space exploration, which was being practiced at the time. Officially called the Discovery Program, it was an attempt to speed up these projects with smaller, lighter, less expensive, and more focused scenarios. And it worked—at least on this mission.

She entered the thin air above Mars safely affixed to the Pathfinder lander, later known as the Dr. Carl Sagan Memorial Station. The lander, in turn, was enclosed inside a protective aeroshell with a heat shield at its back. As it plummeted toward the red soil below, a parachute, with large areas removed to allow the supersonic Martian air to stream through without damaging it, was deployed to slow the craft to a survivable speed after about two minutes. Shortly thereafter, the heat shield was kicked away to expose the lander, which was winched down from the supporting structure on a cable to dangle sixty-five feet below.

At about a minute before touchdown, and one mile up, a radar altimeter was turned on to track the distance between the lander and the hard ground below, now only about thirty seconds away. Then, with less than ten seconds to go, a cocoon of airbags, looking like a diseased cluster of large gray beach balls, was inflated, completely surrounding the lander. This was so unlike the more traditional Viking entry and approach profile it surely raised eyebrows (and perhaps blood pressures) throughout the space community right up until this point. A few seconds later, small rocket engines ignited, burning for only two seconds, drastically and immediately slowing the small craft further. Then the
cable connecting it to the parachutes and engines was cut (this allowed the parachute to drift away and prevented its snarling with the lander), and the craft dropped, free of any influence save for Martian gravity, to impact the surface at about forty miles per hour (far faster than previous surviving craft had). The beach balls absorbed the force, and the entire assembly bounced back into the sky about forty-five feet…then a bit less, and a bit less…In the end, it took fifteen bounces, rolling along at about 30 mph, for Pathfinder to come to its final resting place.

And there it sat, slowly rolling to one flat side of the airbag assembly. Once it settled, the airbags deflated, aided by a triggering device that unzipped the insides of each bag cluster. Once the beach balls were merely flattened, deflated memories, winches built into the lander retracted them to clear the nearby soil and haul them underneath the lander. Mars Pathfinder was a spacecraft that cleaned up after itself.

After nearly an hour and a half, the lander unfolded. It had a base with three “petals,” each a solar panel, and one with departure ramps for the small rover within. The action of lowering the petals finished the job of forcing the lander to sit upright. It was still dark, as the machine had descended to the surface early in the Martian morning—about 3 a.m. local time. Not much more could be done until dawn, so everyone had to be patient. It was July 4, 1997. Millions of miles sunward, a good part of one of Earth's continents celebrated with explosives and rockets similar to those that had delivered Pathfinder to the arid plains of Mars. But here, in the -100 degree wastes, quiet reigned in Ares Vallis.

Ares Vallis had been selected from a long list of candidate landing sites. Years of analysis of the hundreds of thousands of images sent back from previous Mars probes, especially the two Viking orbiters that had arrived in 1976, had given planners almost too much information to sift through. The problem, though, was less with bulk than with detail. The resolution of the Viking cameras, while excellent for its time, was too low to give a really good
idea of what lay below. Anything smaller than about twenty-five feet across was a mere speck. So, while these pictures gave a good general idea of what kind of landscape inhabited broad areas, they were not of sufficient quality to select with exactitude.

But the planetary scientists were undeterred. A lot can be inferred by what
surrounds
an area. The two Viking landers, designed and built in the computer-challenged 1960s and early 1970s, had landed in areas that were barely known (the photos of Mariner 9 and a handful of Viking orbiter pictures were the best they had then), and safety was a much higher priority than fascinating geology and topography. These machines, sometimes referred to today as “Big, Dumb Landers” had to set down while flying blind with minimal feedback from the Martian ground and none from Earth.

Technology had come a long way since then, and even off-the-shelf components (which was what composed most of Pathfinder's data capabilities, another budget-conscious choice) were a quantum leap over what had gone before. So with this added assurance, and the reasonably good images from the Viking orbiters, the Pathfinder team had made its choice of where to land.

Ares Vallis was a flood plain, adjacent to a wide channel, that appeared to have been cut by flowing water—lots of it. The exact landing area was a spot where this channel approached a delta, and eventually opened into Chryse Planitia, the area where Viking 1 had landed (though still over 525 miles distant). If this was what it appeared to be (and it was), lots of different kinds of rocks and minerals should have been washed out of the channel and into the delta. The hope was that Pathfinder would have lots of interesting samples to choose from.

Once the sun rose over Ares Vallis, temperatures shot up to a comparatively balmy 10°F. It was now light enough, and warm enough, to begin operations on the lander. The first images were obtained and sent back to Earth, a twenty-minute trip. The meteorology package was also activated, and weather reports began
streaming in. A quick analysis of the images showed that one of the airbags was not fully retracted and might impede the rover in its operations. This was quickly remedied, and Pathfinder prepared to take more pictures and spend its first full night on a frigid Mars.

There was a heart-stopper at 10:30 that night when the computer onboard the lander stopped sending information. Then, at about 3:20 a.m. the next day, signals received seemed to indicate that for some reason the computer had reset, or rebooted, itself. The reason was not immediately apparent, but it was working again. Everyone breathed a sigh of relief. It was the first, but would not be the last, technical cliff-hanger of the mission.

On sol 2, Sojourner was ready to roll. The command was given: the tiny rover, only about twenty-three pounds in operational trim, “stood up” and rolled down its ramp. Ever so slowly it began to move. Sojourner's optimum speed was about one half inch per second, but it would navigate the ramp down to the surface much more slowly than that. By the end of the day, it had worked its way to the bottom of the ramp and waited patiently for orders. They came at dusk: sniff the soil right where you are. Sojourner spent the night doing just that.

The next day, at 3:45 a.m., JPL controllers “woke” Pathfinder with the song “Final Frontier” from the TV show
Mad about You.
It seemed fitting. Instructions were uplinked to Sojourner to prepare it for an experiment in “soil mechanics,” a fancy way of asking, “How does Martian dirt work?” So the rover was instructed to lock five of its six wheels and turn the sixth one, first one direction, then the other, grinding away at the dirt. By observing the reactions of the surface to this abrasion from the tiny stainless-steel wheel, the geology team on Earth would be able to divine much about the real estate close by the Pathfinder lander.

At the conclusion of this Martian version of smoking tires, Sojourner would begin its historic traverse to Barnacle Bill, the first of many rocks to be visited in the immediate area. Now, the word
traverse
might be misleading…it conjures thoughts of a
long overland voyage. In this case, the total trip from Sojourner's position at the base of the ramp and Barnacle Bill was a slim fifteen inches! Still, this was a new technology on a new mission on a distant planet, so everything had to be planned with care.

Sojourner started her short journey. While this was under way, the lander began work on a so-called monster-pan, a complete 360-degree sweep of the landing area. The results were spectacular. After years of studying the Viking lander images from the 1970s, these new, highly saturated high-resolution pictures were simply breathtaking. They showed a whole new Mars. Not only was the topography and weathering different from that shown in the Viking landing zones, but the details of rock surfaces, types, and general weathering were far more evident.

The images in general were so superior that when combined with orbital photos from the various probes that had been investigating Mars from high above, assumptions could be rapidly made about the surrounding terrain.

One thing became clear right away: their interpretation of the landing area as resulting from water flows was spot-on. As one scientist put it, the flooding was so catastrophic that it could have filled Earth's Mediterranean basin. That's a lot of water for a desert planet. Water-transported deposits were seen nearby. Rocks such as Barnacle Bill had small “moats,” or eroded depressions, around them. Areas of bright and dark soil were seen, indicating wear. And the rocks nearby appeared to be of differing origins, if not differing types altogether. It was, as one scientist phrased it, a geological grab bag. And this offered opportunities to have Sojourner “sniff” a variety of nearby rocks, presumably washed down from different regions in Mars's wet and wild past, to build a better picture of the planet's history.

As if to underscore this, the next rock visited, Yogi, was markedly different from Barnacle Bill. It was more primitive, not having experienced the heating, cooling, and general geological nightmares that the previous rock had.

These were exciting times. The first machine to land on Mars in twenty years was operating perfectly, and gathering reams of new and detailed data. And as usual, it was exceeding expectations.

By the time Pathfinder had been on Mars for six weeks, the mission was still proceeding well, but some glitches had popped up. On August 16, the flight computer on the lander had reset itself. It had not asked “DO YOU MIND IF I REBOOT?” or sent any other indication; it simply restarted of its own accord. Why this happened was not known, but at the time it was suspected that the temperature extremes experienced on the planet this time of year were severe enough to cause issues with the computer's circuitry. In any case, JPL worked the problem, sent a command to the lander to ensure proper aim of its high-gain antenna, and through this process reestablished contact at about 10 p.m. on the seventeenth. The sense of relief was palpable. However, this was neither the first nor last time this problem would rear its ugly little silicon head, and each time it did, the concern increased.

Soon controllers were receiving images from the lander again, and immediately another problem became apparent: Sojourner, still not far from the lander, was stopped on a rock called Wedge, and for obvious reasons. It had been heading toward another rock named Shark, and the onboard sensors, ever vigilant against hazards, had sensed a tilt that was more than it was willing to accept. The small computer shut down the rover and waited patiently for advice from Earth. After an intense conference, the team worked out a new course and sent the commands skyward. Sojourner headed off to Shark and the area called Rock Garden beyond.