If there ever was a classic success story of the exploration of Mars, the endurances of the two Mars Exploration Rovers, Spirit and Opportunity, and their discoveries would be the perfect story. Mars is not an easy planet to explore. Over half of the spacecraft failed either enroute, upon arrival, or shortly thereafter, but these rovers have restored faith in the exploration of Mars. Their over five years of adventures have made the surface of Mars as familiar as the deserts on Earth. Neither rover was expected to last more than three Earth months, and yet both have survived winters as severe as -150ºF, and a blinding global dust storm.

The goal of the rovers was to “follow the water” in order to determine if Mars was ever hospitable for life. The two Viking Landers in the late 1970’s did not find any trace of life, past or present, but their searches were restricted to the landing site and by the length of the soil sample arm. It was necessary to be mobile so that a larger area could be explored. The Sojourner Rover in 1997 proved that mobility was possible and also important as it found different type rocks wherever it roamed. Two regions on Mars that looked promising for having had a watery past were Gusev Crater, which appeared to be fed by water from the southern highlands through Ma’adim Vallis, and Meridiani Planum, which is covered with the mineral hematite that normally forms in water. Spirit was chosen to land in Gusev Crater and Opportunity at Meridiani Planum.

The Spirit Rover blasted off from Earth on June 10, 2003 and bounced to a landing on inflated airbags within Gusev Crater on January 3, 2004. The scenery was beautiful with a vast rusty desert and hills in the distance under a dusty, salmon-colored sky. Spirit began roving within days examining rocks, but everything came to a screeching halt on January 21. Communication was lost for several days and it was feared that the mission would end all too soon. Mission scientists found a flaw in Spirit’s flash memory that was causing it to constantly reboot, but fortunately new software was uploaded to correct the problem. It worked and Spirit looked forward to years of exploring. Spirit had already determined that the landing site was not a dry lakebed, but instead was filled with ancient lava.

There was no evidence of water anywhere on the dusty plain, so Spirit drove onwards to explore Booneville Crater. It was about 660 feet from the landing site and 825 feet wide. Spirit reached the rim on March 11 and it was hoped that the crater would reveal older geology possibly altered by water, but it ended up being nothing more than a dusty bowl. The warranty expired in early April as Spirit exceeded its official expectations for days of operation and distance traveled, but the best bet in finding clues for water were in the hills, therefore Spirit was sent on the long 1.2-mile drive to the Columbia Hills, which were named to memorialize the Space Shuttle Columbia disaster of February 1, 2003. As Spirit left Booneville Crater for the hills it finally found older geology that appeared to be influenced by water. There were rocks enriched with bromine and chlorine, and contained hematite, which often forms in water.

Spirit is equipped with a rock abrasion tool that is capable of brushing and drilling into rock and analyzing the chemistry. Fortunately, this tool did not wear out for many years past its designed lifetime. However, the right front wheel began drawing twice as much electric current as the other five wheels. It was decided to drag the wheel and to drive the rover backwards. The problem went away and normal driving resumed for a time, but the wheel failed altogether on March 13, 2006. In spite of the mishap, Spirit was resilient enough to continue roving, exploring, and discovering.

Winter was setting in as Spirit climbed up Husband Hill in the Columbia Hills, named in memory of the astronaut Rick D. Husband, one of the seven astronauts who died in the Space Shuttle Columbia disaster. It was critical to reach the summit as Spirit would be receiving less sunlight for the solar panels to keep it charged as the Sun sank lower. Operations would have to slow down considerably as dust, which further hindered it from charging properly, accumulated on the solar panels. During its climb up the West Spur of Husband Hill, Spirit found a violent history where the rocks were probably formed from a volcanic eruption or meteor impact. These rocks were goethite, an iron oxide mineral that requires liquid water in order to form. The rocks also contained sulfur, bromine, and chlorine, and were softened probably from groundwater and were similar to sandstone.

Good luck was on Spirit’s side in mid-March 2005 as a dust devil most likely swept the solar panels clean restoring its power. It would now be able to do some astronomy at night instead of spending the entire night resting and recharging. It was able to observe the two moons, Phobos and Deimos, and could determine how dusty the atmosphere was by monitoring the amount of light each gave off for several nights. It also observed the Sun in the same way to measure the dust and also observed the clouds high overhead. It observed beautiful sunrises, sunsets, meteors streaks, several of the orbiters sailing aloft, and a bright star, which was its home, Earth. It has observed hundreds of dust devils racing across the surface every day during the warmer seasons. The average surface temperature is around -64ºF, but the intense cold has not hampered Spirit. It survived the severe winters in the Columbia Hills by pointing its solar panels towards the Sun and limiting its activities by not driving. To do this, it had to sit pretty much idle on a hillside that is sloped just enough to optimize the angle of the solar panels to the sunlight striking them. Fortunately there are many areas in the hills where it can do this and is one good reason why Spirit may never leave the hills for the flatter plains.

A pair of violent dust storms during 2007 and 2008 nearly ended Spirit’s life as they cut the vital sunlight causing the power levels to fall dangerously low, but the storms cleared soon enough that Spirit was able to resume exploring. Spirit became trapped in a patch of fine sand on May 6, 2009 when the crusty surface it was traveling over gave way and it ended up to its hubcaps in the fine sand. Efforts are under way to free Spirit as of this writing. It is possible that Spirit may be forever doomed to remain in this spot for eternity on the edge of a fascinating rocky outcrop known as Home Plate. If it is freed, Spirit will be very busy roving around this area and among the hills exploring and discovering for perhaps months and years to come. Spirit’s fate is in the hands of Mars, and Mars has never been kind to any spacecraft.

Spirit has revealed that Mars has had a history of liquid water shortly after its creation probably 3 to 4 billion years ago. Then something happened with the climate that led to the dry, barren Mars of today. Spirit has been around so long now that it is almost like a living person, a true geologist, and will be missed when its end does arrive. Meanwhile, on the opposite side of Mars…

TO BE CONTINUED…