Mars was being carefully scrutinized by the Spirit Rover, when out of the dusty, salmon-colored sky on the opposite side of the planet, a cluster of giant airbags came bouncing down along the surface and rolled into a small crater. Moments later the airbags deflated and the petals opened to reveal the Opportunity Rover. From that moment on, Opportunity virtually stole the show from Spirit with its almost continual discoveries.
Opportunity was launched July 7, 2003 and landed on Mars on January 25, 2004. The landing was like a golfer’s dream as it rolled into the middle of a crater hardly 65 feet across on an otherwise flat plain. As soon as it started observing it saw that the crater wall was lined with bedrock. This was definitely an old part of Mars that had been excavated by a meteor impact. Another interesting characteristic of Meridiani was the unusually dark landscape. The soil was covered by countless, tiny, dark beads, which were nicknamed “blueberries”. Opportunity went to work to find out what these were. It was hard to get a spectrum of these berries as they were scattered, but there was an area where dozens of them collected into what was called the “Blueberry Bowl”. Opportunity was able to determine that these blueberries were the richest source of hematite in the area. It usually forms in water, but more exploring was needed. Opportunity spent a full two months studying the blueberries and bedrock in the crater it rolled into, which was called Eagle Crater in honor of the Apollo 11 lunar module, Eagle. Everywhere the evidence pointed toward a watery past. Meanwhile, Spirit was still months away from detecting any such proof.
The big announcement came on March 2, 2004 that liquid water once drenched the surface of Mars, or at least in the area where Opportunity was roving. Evidence was everywhere as the rock cavities had salt crystals indicating the presence of water that formed them. There was also sulfur, which reinforced the fact that the rocks had to form in water. The mineral known as jarosite was found and there is no other way for it to form except in acidic water. This proved there had to be groundwater at one time, but it was not known if there was standing water on the surface. Opportunity studied the bedrock in great detail in Eagle Crater and found particles and structure that could only be formed by ponding water and wave action.
The next question was how long the water remained before it dried up and the only way to find out was to drive to another crater and hope to find deeper bedrock. Opportunity headed for Endurance Crater where it arrived on April 30, 2004. The crater was 625 feet in diameter and layered with bedrock yards thick. Opportunity was able to enter the crater, but it stayed close to the rim, which revealed complex layering. Opportunity made good use of its rock abrasion tool to once again reinforce the discovery that most of the rocks were formed in water. There were blueberries everywhere Opportunity roamed and the layering history in Endurance Crater pointed to a Mars that was wet for quite a long time. There was sulfur rich rocks laid down in shallow water and loaded with the hematite blueberries. This was a big success story in the exploration of Mars and it would seem that Opportunity did not have to explore any further, but a big gamble was made to send her more than three miles away to Victoria Crater, an even larger crater, to see how far back in the history of Mars it could go.
Opportunity was primarily a geologist, but it was also an astronomer and a meteorologist like Spirit. It observed the two moons at night, Phobos and Deimos, but better yet it observed them eclipsing the Sun. These moons are too small for a total eclipse, but it was fascinating to see such an alien sight of their potato-shaped silhouettes against the Sun. Opportunity also observed sunrises and sunsets, monitored weather and dust conditions along with dust storms. One dust storm during mid-2007 was so powerful that it became global and blocked 99% of the sunlight, nearly killing Opportunity.
By Christmas 2004 Opportunity left Endurance Crater and drove to its jettisoned heat shield. This gave engineers a good look at how it performed and will act as an aid in designing future heat shields for Mars landings. The area where the heat shield impacted the surface was also studied to see what it might have dug up, but the ground was so hard that it was only compacted. Next to the heat shield was an unusually dark and pitted rock that seemed out of place and it turned out to be a nickel-iron meteorite, the first ever seen on another planet. The next journey was ambitious as it was not certain if Opportunity would last long enough, but a chance to explore the large crater, Victoria, which is six times larger than Endurance, was too good to pass up. The only problem was that it was more than three miles away and Opportunity had to cross a vast unknown region known as the “Etched Terrain”. It was a mottled area and was not known if it would be easy to traverse.
Unfortunately the “Etched Terrain” was literally a sand trap and nearly immobilized Opportunity forever. It was a field of small, fine sand dunes and bare rock. Opportunity became stuck in one of the dunes on April 26, 2005. That one-foot high dune became known as “Purgatory Dune” and Opportunity remained stuck for nearly six weeks while scientists back on Earth tried to devise a way to get it out safely by using a set-up involving a full-scale test model of the rover and duplicating the dune with fine sand. Patience paid off on June 4 as Opportunity was freed and continued the long journey toward Victoria. It finally arrived at the rim of Victoria Crater over a year later on September 26, 2006. It was a beautiful sight peering into the crater, which revealed thick layers of bedrock waiting to be analyzed. Opportunity drove part of the way around the rim for the next several months to see if there was an easy way to go into the crater and, more importantly, get back out. It did not find a better location, so it returned to its arrival point, known as Duck Bay, and enter there, but then a near-deadly dust storm struck.
Opportunity survived the frightening storm and when the dust settled it finally entered the crater on September 11, 2007. It did not go too far in as the slopes were steep and slippery and there was a huge dune field in the center. It continued its exploration into 2008 by analyzing the layered bedrock and unlocking clues to the watery past of Mars. Victoria would be a beautiful final resting place for Opportunity, but it still had a lot of life so by the end of August 2008 it was sent out across the vast plains of Meridiani for the 7-mile, 2-year long drive towards a larger crater called Endeavour to see what other surprises and discoveries lay ahead. Opportunity has been so successful and entertaining that it has gained enough affection to be nicknamed “Oppy.” It will be a very sad day when the end arrives.
Even when Spirit and “Oppy” are gone, there will be a new, larger rover writing a new chapter on Mars early in the coming decade. The Mars Science Laboratory Rover, known as Curiosity, is scheduled to launch in late-2011. It is as large as a small car compared to the golf cart-sized Spirit and Opportunity and the microwave-sized Sojourner Rover. It is the scientists’ dream machine bristling with hi-tech equipment and will be a fitting tribute to the three rovers that pioneered its way.