Amidst the breakneck pace of increasingly disturbing news commanding the headlines in America and around the world, something extraordinarily wonderful, something unifying for all Earthlings happened on the Red Planet, and it went all but unnoticed.
The Mars Explorations Rovers (MER) team quietly completed 14 years of surface operations and then Opportunity, the longest-lived robot on another planet, kept on roving into the mission’s 15th year and a whole new Martian scene. It is an unparalleled achievement in planetary exploration.
Spirit and Opportunity were originally sent to opposite sides of Mars on three-month exploratory tours to look for signs of past water and perhaps characterize any places that may have been potential habitats where life could have emerged. The twins met those science objectives in their primary missions and then exceeded everyone’s wildest dreams. With their uncannily individual personalities and quirks, they also helped produce the most experienced Mars rover experts on Earth.
Inspired by the wonder of it all and the knowledge and technology that could be reaped, NASA’s motivation here was simple and pure: go where no Earthlings have gone before (but have always wanted to go) and explore, try to find out if Mars really was once like Earth, and show everyone this distant land looks like.
“It’s a remarkable thing,” reflected MER Principal Investigator Steve Squyres, of Cornell University. “It’s important to not lose that sense of wonder and that sense of how fortunate we are to be able to do what we do. Nobody got into this to get rich. Nobody got into this to get famous. We got into it because we love that feeling of exploration.”
Together, the MER team and its robots have and continue to explore, demonstrating what can happen when people bound by tried and true ethics work together for a common goal and a greater good. The upshot is history in the making: 14 years later Opportunity and the MER team are still roving, still setting records, and still making important discoveries, even with the bounty of data Spirit sent home years ago.
“Spirit and Opportunity helped to revolutionize our understanding of Mars as a planet,” said Planetary Society President Jim Bell, the lead scientist on the rovers’ Panoramic Cameras (Pancams), of Arizona State University (ASU). “Both rovers found evidence of ancient, habitable environments along their traverse paths over the years, helping us to provide ‘ground truth’ for orbital remote sensing data, and substantially extending the capabilities and interpretations that we can gain from those orbital perspectives.”
The discoveries of Spirit and Opportunity also helped to inform the choice of instruments and landing site for Curiosity, which continues to make discoveries of her own in Gale crater. “This ‘symbiotic’ relationship is a result of NASA having a true Mars Program, where one mission can influence the next, and the pace of exploration is sustained over many years,” Bell said.
Deep in the west rim of Endeavour Crater, Opportunity spent New Year’s Day recharging and taking a brief respite in her winter exploration of Perseverance Valley. From her position just uphill from a fork or split in the primary trough or channel in the valley, imaged everything in sight and then took Yogi Berra’s advice and took the fork in the road and entered a rock-filled scene unlike any other the mission has explored.
“Mars continues to surprise us,” said Deputy Principal Investigator Ray Arvidson, of Washington University St. Louis (WUSTL). “We’re seeing stuff we’ve never seen before, we have new science objectives, and there will be brand new discoveries. Perseverance Valley really is a brand new mission and we’re right on top of it trying to get the data to answer the key questions.”
Mars, apparently, approves. A series of wind gusts coming up from the floor of the crater whisked a substantial amount of dust from the solar-powered rover’s arrays in January, leaving them almost clean. “Our energy has jumped way up,” confirmed MER Power Team Lead Jennifer Herman. “I’ve been hoping we would see some dust cleaning, but I wasn’t expecting to see this. We’re in really good shape.”
So as Opportunity continues her trek through Perseverance Valley and into Year 15 of roving Mars, the future, all things considered, is as bright as it could possibly give...and the mission is poised to command the headlines again in the New Year.
14 Years of Memories from the Road
Spirit and Opportunity were green-lit for flight in the summer of 2000. Designed to be twin robot field geologists, they would be equipped with seven science instruments, including cameras and would be delivered to opposite sides of the Red Planet. They were a critical part of a NASA Mars Program mission to “Follow the Water” or to find evidence for past water, and perhaps signs of habitats long gone where life once might have emerged.
Getting the rovers built, tested, buttoned-up and to the Cape was a constantly challenging adventure. If they were to meet the 2003 launch window, Project Manager Pete Theisinger and the engineering development team, along with Squyres and his Athena Science Team, and the thousands of people who played roles in the creation of these ‘bots, had just 36 months to go from a Power Point presentation to two fully equipped and operational rovers packed into their spacecraft, and on the launch pads at the Cape. With but a breath to spare, they made it.
Opportunity left Earth on July 8, 2003 from Cape Canaveral in a picture perfect, blue-sky launch. Three weeks earlier, on June 10th, her twin Spirit blasted off, soaring into space on a similar summer day. It should have been a triumphant moment and it was. But for Squyres, elation was elusive.
“In all the years of struggle, one of the things that kept me going was this vision of what launch would be like,” he reflected. “It really surprised me because when we got there, it felt very, very different than I anticipated it would. It was a very bittersweet feeling.”
As Spirit and then Opportunity disappeared, Squyres was moved by the emotion of reality: the rovers had exited Earth forever. “It was hard to say goodbye,” he said.
Seven months later, on January 3, 2004 Pacific Standard Time (PST), Spirit arrived at Mars first, dove into the Martian atmosphere, survived the six minutes of terror, and hit the ground in Gusev Crater protected by airbags. After bouncing for more than 16 minutes, the spacecraft stopped. The robot signaled home. Within a few hours, she sent her first picture postcards, taken with her Navigation Camera, to Earth through the Mars Odyssey Orbiter and the giant antennas of the Deep Space Network (DSN).
Opportunity followed three weeks later, bouncing down on January 24, 2004 PST and rolling right into a small impact crater on the plains of Meridiani, the team called Eagle Crater. It was Earth’s first interplanetary hole-in-one. In the wee hours of the next morning at the MER mission control at the Jet Propulsion Laboratory (JPL), this robot’s first images came streaming in and left everyone on site even more jaw dropped. Right there, just in front of Opportunity was the prize the MER scientists had been hoping they might find: bedrock.
Those landings were moments never-to-be-forgotten for everybody who was at JPL, certainly the best moments imaginable for the Entry, Descent and Landing System Manager Rob Manning and the EDL team that night. They were against-all-odds achievements that moved people far and wide across planet Earth. As then JPL Director Charles Elachi encouraged people from the dais at the Opportunity landing press conference: “Go outside and look up at Mars tonight. We have two rovers up there.”
For MER Project Scientist Matt Golombek, the landings were the moments he ranks as his favorites. With a “day job” of selecting landing site candidates on Mars, he had recommended the site chosen for Pathfinder/Sojourner, and he played the lead role at JPL in researching and selecting both Gusev Crater plains, where an ancient lake once might have been, and Meridiani Planum, where hematite, a mineral that forms in water, lit the orbital mineral detectors.
“What you actually do when you make the landing site selections is predicting that the surface is safe for landing and for roving,” Golombek explained. The landing site committee members used Viking data, and for Spirit and Opportunity added data from instruments onboard the Mars Global Surveyor data, and went the distance by predicting the amount of dust to be expect at the sites, along with other environmental considerations. NASA, of course, made the final decisions.
When Spirit’s and then Opportunity’s initial images appeared on the monitors at JPL and everyone got the first clear views of what the surface was like, Golombek was “pretty darn happy.” Summing up those moments with his characteristic laughter, he said: “We nailed it.”
From the rock strewn terrain of Gusev to the bedrock shock of Meridiani Planum, Mars rocked the Internet, as more than a billion people logged on NASA, JPL, and mirror websites to get a glimpse of this magically desolate planet.
Planetary scientist Abby Fraeman, who grew up with the rovers, remembers that night too. She was 16 then and one of Student Astronauts on The Planetary Society’s Red Rover Goes to Mars Project. “When those first pictures came down from Eagle Crater and everyone was going: ‘I see bedrock. I think I see cross bedding in the bedrock.’ I’m wondering: ‘What is crossbedding? What is bedrock? What does that mean?’ At that point I hadn’t had any geology classes, but I really wanted to stay and be one of the people who could look at those rocks and understand what they were seeing.”
That experience put Fraeman on her career track that led to her current position as MER Deputy Project Scientist. “From the perspective of a college student, there was a future for exploration of Mars,” she said. “That, for me, was very bright and exciting. I figured if I found something more interesting, I’d change my major, but I never found anything cooler than working with the rovers on Mars.”
There were a couple of frightening problems early on. As Opportunity landed, Spirit had just gotten back to work after the team’s software engineers pulled the rover out of a confounding reboot loop by fixing a software ‘bug.’ And, perfect as her landing was, Opportunity had and electric heater at the shoulder joint of her robotic arm that was stuck in the ‘on’ position and draining her power. The team would soon resolve that problem by commanding the rover to shut down each night, the time when the heater was usually running. They called it DeepSleep and it’s a power-saving strategy Opportunity uses to this day.
With those issues resolved, Spirit and Opportunity began their adventures. Both rovers found evidence of past water and each met the mission objectives during their primary 90-day missions. In early March 2004, Opportunity still inside Eagle Crater, found evidence of past liquid water, in sulfates and minerals, including a rare mineral known as jarosite that forms in the presence of water, and other geologic structures that form by way of aqueous action. It was evidence, the MER science team hypothesized, that indicated an ancient salty sea was once present there, once that could have been a habitat suitable for the emergence of life.
“That was pretty big news for us if you think back to 14 years ago,” said Golombek. “People were still arguing about whether there was water on Mars and we had the first evidence from a rover on the surface, evidence that was pretty much indisputable.”
The hematite that drew them to the Meridiani plains, the MER scientists found, is all around the surface, eroded from the strata and concentrated on the surface in spherules – blueberries, as the team dubbed them, after the color they took on in false color images – and some were still embedded in outcrops. The soils, they found, are fine-grained basaltic sands mixed with dust and sulfate rich outcrop debris.
On the other side of the planet, Spirit, found mineralogical evidence for past water in the fractures of a two-foot tall volcanic rock named Humphrey while picking her way through the rocky terrain to get to Bonneville Crater. With the mission’s first extension, this rover headed across Gusev to the Columbia Hills, a collection of seven hills, each of which the MER team named for one of the seven astronauts who died on Columbia’s final, tragic flight in February 2003.
Opportunity, meanwhile, roved out of Eagle Crater and headed for Endurance Crater. There, she became the first rover to drive into a crater on Mars. Not long after that, she became the first robot to inspect her own heat shield, and discover an intact meteorite. Then she took off on a journey to an impossible dream destination, Victoria Crater.
In the spring of 2005, Spirit became first robot to capture images of dust devils in action from the surface, and on her Sol 421st sol (March 10, 2005), she shot captured two. Historically, there was a dust devil identified in a single image from the Mars Pathfinder mission in 1997.
No one expected Spirit to last through the first winter, but the rover made it to the Columbia Hills in June 2004 and found north-facing slopes where she could position herself so her solar arrays pointed toward the winter Sun. By “hopping” from one north-facing slope to another, like a frog from lily pad to lily pad, the rover showed she had the right robot stuff to survive and pioneered what would become the mission’s winter survival strategy.
In late August 2005, Spirit reached the summit of Husband Hill, named for Rick Husband, Columbia’s final Commander. Then in late September 2005, she hiked to the hill’s second summit, earning the distinction of being the first robot to climb a hill as tall as the Statue of Liberty, about 82 meters or 270 feet. It was impressive for a robot that wasn’t designed for mountaineering.
"Spirit explored just as we would have, seeing a distant hill, climbing it, and showing us the vista from the summit,” said Squyres. “And she did it in a way that allowed everyone on Earth to be part of the adventure."
At Meridiani, Opportunity was roving carefree across the plains toward Erebus Crater until she hit a sand ripple in late April 2005. Stuck up to her ‘hubcaps,’ for six weeks, it would be a lesson hard learned. By June, the robot that was garnering acclaim as ‘the rover that loves to rove’ managed to free herself and get back to where she once belonged, roving across the plains.
Back on the road south toward Victoria, Opportunity stopped at Erebus Crater and spent about five months between, October 2005 and March 2006, studying the large, shallow, partially buried hole in the ground. During this time, she broke her shoulder joint and had to adapt to driving with her IDD or robotic arm partially deployed, looking like she was sporting a fishing pole. No big deal. It wasn’t anything that could stop this rover.
Opportunity finally arrived at Victoria Crater in late September 2006, pulling up to one of the scallops in the rim, which the team christened Duck Bay. For the next nine months, the rover explored a good part of Victoria’s rim. Then in June 2007, she returned to Duck Bay where the team planned for the rover to drive into the crater.
Over at Gusev, Spirit had hiked down from Husband Hill’s second summit heading for Home Plate, a circular plateau, about 90 meters in diameter that was too intriguing not to check out. However, near the bottom of the hill, in December 2005, the robot came across a strange looking outcrop. The team members commanded her to stop and use all her instruments to examine this outcrop soon named Comanche.
Mars Science Team member Richard Morris, senior planetary scientist and manager of the Spectroscopy and Magnetics Laboratory at NASA's Johnson Space Center (JSC), knew from his first look at Spirit’s Comanche data from the iron-detecting Mössbauer spectrometer that something was different. It would take Morris and others on the MER Science Team years to find it, but the rover had sent home data rich with undeniable evidence of past water.
By February 2006 Spirit was exploring Home Plate and spent several months checking it out before heading for McCool Hill, named for Columbia’s pilot Willie McCool. The team planned for Spirit to survive the mission’s second winter on that hill, just as she had on Husband Hill. But that was not to be.
The steering actuator for Spirit’s right front wheel broke. No longer able to climb hills and with winter coming on, time was running out. In late May 2006, the mission managers decided to reverse the rover’s course. The robot turned around and drove, valiantly it seemed, backwards, dragging her lame wheel, descending several meters from her climb toward a north-facing slope on McCool Hill to seek haven on a slope in Low Ridge. She managed to settle in just in time for the mission’s second Martian winter.
Months later, Spirit emerged from the mission’s second Martian winter and roved back to Home Plate. "We decided to go back to Home Plate, once the Martian winter ended, because it is one of the most interesting places that we've found on Gusev Crater," Squyres said then. It was a good call. Spirit was about to hit a home run for planetary science there.
In May 2007, members of the MER Science Team were hypothesizing that Home Plate was composed of debris deposited from a hydrovolcanic explosion. That same month Spirit had uncovered a patch of light-toned, almost white soils as she was on her way to a silica rich outcrop chosen by the scientists near the base of Home Plate.
Steve Ruff, the Miniature Thermal Emission Spectrometer lead scientist, of ASU, was already on the trail of opaline silica. “I knew this opaline silica that we were beginning to recognize from Mini-TES was important, but I didn’t know at that time where this was going to lead,” he recalled. “At the time, we were struggling with dust contamination on the Mini-TES mirror that made the spectra for Mini-TES data difficult to interpret. But there was enough there that I could tell that what we were seeing and where in the landscape we were seeing more of this stuff.”
Spirit was already in place on silica-rich outcrop when Ruff and the team noticed the trench the rover had made as she dragged that right front wheel. “We measured the trench with Mini-TES, and again we saw a strong indication of opaline silica,” Ruff said.
Once work was done on the outcrop, Spirit drove over to the patch of scuffed up white stuff and checked it out up close. Turned out it was near pure silica. “It was a great moment,” said Ruff. “I can’t say it wasn’t exciting to drive up and see nearly pure opaline silica. It really made the story that much firmer and clearer for us.”
Silica at Mars has become a major highlight in Ruff’s career. Even after Spirit’s mission was over and to this day, he has been researching Earth analogues. Despite being seriously challenged by other scientists along the way, his comparative analyses and findings in Spirit’s data have successfully convinced most planetary scientists that this rover uncovered hot springs and sinter deposits. “Now he’s trying to convince the community and the 2020 project to go there and drill them,” said Arvidson, noting that Gusev is now one of the three final candidate landing sites for NASA-JPL’s 2020 rover.
“As I’ve learned more in fieldwork in exotic places and in lab work, that discovery is becoming clearer to me, and the different questions that remained after the finding are now being answered with a decade of follow-on work,” said Ruff. “The story of an ancient hot spring producing this rock called Silica Sinter is really quite robust now.”
Interestingly, the story has turned into something of a hunt for potential biosignatures as a result of that follow-on research. Most recently, Ruff and colleague, ASU Professor Jack Farmer, conducted fieldwork at El Tatio, a high elevation hot spring system in Chile that “opened up the possibility that the silica at Home Plate may actually feature structures that could be stromatolites produced by a combination of geology and biology,” Ruff said.
“Spirit's unexpected discovery of concentrated silica deposits was one of the most important findings by either rover,” Squyres declared then. “It showed that there were once hot springs or steam vents at the Spirit site, which could have provided favorable conditions for microbial life.”
As Arvidson summed it up this past month: “In the end, 20 years from now, the overall set of deposits associated with Home Plate and the likely discovery hot spring deposits is the science discovery for which Spirit will be remembered.”
Meanwhile, as Spirit continued research on the silica near Home Plate, the dust in the atmosphere was getting thicker. By July 2007, the regional dust storms that were turning the skies an opaque dark rusty red merged into a monster, planet-circling storm. Although both rovers were feeling the effects Spirit, Opportunity was literally in the dark. NASA estimated that 99% of direct sunlight was blotted out over Meridiani, leaving only the limited diffuse sky light to power the rover.
“We were spacing the downlinks from Opportunity to once every four sols in order to conserve energy,” remembered Herman. “Every time you downlink data it takes energy and we didn’t want to deplete any more power than we had to. The sky was dusty and the energy was low, and the rover was getting cold. We got our downlink, sent up a plan – and then we waited. Everyone thought Opportunity was going to die.”
Time passed. Slowly. But it did pass. On the appointed morning, Herman settled in behind her console in Mission Control with probably 10 or 15 people standing behind her. Squyres, then on sabbatical at Caltech, was there on site. Everyone was waiting to see if Opportunity had survived.
Finally the rover’s telemetry appeared on Herman’s monitor. “’We’re still alive!’” she said. “And the rover was actually improving. We were so happy. We all hugged. I cried. It was really, really wonderful.”
As the dust storm began to dissipate, Spirit checked off her 1,282nd sol on August 11, 2007 and became the second longest working lander on the surface of Mars. She surpassed the longevity of the Viking 2 lander, which was powered by a nuclear cell. Spirit, of course, was primarily powered by the Sun. The Viking 1 lander, which had logged 2,245 sols of operation, was now in her sights.
By September 2007, Opportunity had shaken off the dust best she could and was ready to begin that detailed study inside Victoria Crater. “The most stressful, memorable moment was Sol 1291 (September 11, 2007) when we did the toe-dip into Victoria,” said Rover Planner Paolo Bellutta, who had been assigned the tasks of defining and charting the best entry and egress points. He had collected imagery and analyzed telemetry for months, but still he was anxious. This was, after all, a rover on Mars.
After Bellutta reviewed his crater entry plan at the Science Operations Working Group (SOWG) meeting, Squyres asked simply and directly: “Are you sure?"
“I don't think I have been that nervous before,” Bellutta recalled. “But I trusted all my work, so I said ‘yes.’” And the command to make the toe-dip was sent off to Opportunity.
That night, Bellutta had a weird, kind of back-to-the-future nightmare. A child and his father were visiting Duck Bay on Mars. As they peered into the crater, the child turned to his dad and asked: “So why did they go down here?"
Out of Dreamland and back to reality, the answer of course was simple: to explore. And that’s what Opportunity would spend the next year doing, examining the various strata inside the crater. The MER scientists identified three distinct strata that show compositional trends with depth, similar (but with some differences in detail) to what the rover found in Endurance crater, showing that water-induced alteration was regional in scope in Meridiani. They also found that the layering in the crater wall preserves evidence of ancient wind-blown dunes.
On Earth, the MER ops team scored another historical first of its own, years before the “watershed moment” of 2017-2018 – and no one was ever trying for this achievement. On February 22, 2008, the entire tactical operations team for the mission, both onsite at JPL and offsite at remote institutions, was female. And it wasn’t planned. It just happened as a result of scheduling. "It was fabulous," said MER Mission Manager software engineer Cindy Oda then. "You know the joke about women drivers. Well, now women are driving on Mars, commanding rovers."
With some final imaging of Cape Verde, one of the promontories that forms Victoria’s rim, Opportunity’s work inside the crater was deemed complete and the rover made its exit. In September, NASA and the MER team announced this rover’s next destination: a giant crater to the southeast. At 22-kilometers (13.7-miles) in diameter and 300 meters (984 feet) deep, it is more than 20 times larger than Victoria Crater, “staggeringly large compared to anything we've seen before," as Squyres put it. The team named it Endeavour after HMS Endeavour, Lieutenant James Cook’s British Royal Navy research vessel.
It was a hugely ambitious goal, especially given that Opportunity was 4 years and 8 months into a mission originally "warrantied" for 3 months and the distance from Victoria to Endeavour is slightly more than the distance the rover had traveled since landing in Eagle Crater. For some outsiders, it seemed preposterous, even for a rover that loves to rove. "We may not get there," Squyres admitted then. "But it is scientifically the right direction to go anyway."
Just days after the announcement, on Sol 1662 (September 26, 2008), Opportunity officially began her incredible journey that would take her about 12 kilometers (about 7.5 miles) to the southeast across the plains and farther back in Martian time.
Over at Gusev, Spirit spent most of 2008 surviving. First, there was the mission’s third Martian winter to get through. The rover managed to clear it by parking right on the edge of Home Plate, her arrays to the north and the winter Sun, conserving energy and waiting out the brutal cold.
Her odds for survival seemed to improve significantly in April 2008 as the dusty skies cleared dramatically over at Gusev, enabling the robot to maintain better-than-anticipated power levels that month. And that meant the engineers "probably won't have to do anything extraordinary" to keep her alive, then-MER Chief of Rover Engineering Jake Matijevic said at the time. But there were still months to go before the Martian spring.
Then in November 2008, a dust storm struck the ‘bot dead on and dropped her energy levels to 89 watt-hours, the lowest recorded on the mission. But on November 13th, the rover phoned home. “It was a good day on Mars today,” Squyres told The MER Update then.
Arrays thick with dust, Spirit survived both winter and another dust storm and finished her tour of the top of Home Plate. Then she drove off the mound, ultimately heading for the next destinations.
By April 2009, she was cruising along the western side of the circular mound, on the way to the next target destinations to the south named after rocket pioneers Robert Goddard, and Wernher Von Braun. Suddenly, while driving along Home Plate the rover caught the edge of a small crater hidden by the sand that filled it and was stuck. By early May, it was clear her left wheels were seriously dug in. After months of research on Earth, in November 2009 the team began sending commands for the rover to begin extricating itself.
When the first extrication strategy failed, the team switched to Plan B and by late January 2010 Spirit was beginning to make real progress. But the onset of winter brought the rover to a stop. Unable to move to a Sun-facing slope, she was forced to shelter in place.
Spirit downlinked a communiqué on March 22, 2010. Shortly after that, the ops engineers assumed the rover tripped the low power fault and went into a hibernation mode, to rest and try to collect enough sunlight to keep her survival heaters available and the mission clock running. That’s what the rover was programmed to do.
About three months later, in June 2010, ostensibly while Spirit was in hibernation, Richard Morris and MER Science Team colleagues announced that Comanche is harboring magnesium iron carbonate, and a lot of it. In their Science journal article, they theorized that it could have been produced by a hydrothermal system.
It was evidence for a past watery environment more suitable for life than any other either MER had found, a place where near neutral water existed, water the likes of which we would drink on Earth. And it was a discovery Squyres called “one of the top five findings of the entire mission.”
That carbonate discovery led to more questions for Ruff. “One of the interesting problems with the Comanche hypothesis is that is requires carbonates to have been present somewhere else and some other time in Gusev Crater from which you could then pump hydrothermal fluids through and dissolve the carbonates and re-precipitate the carbonate in Comanche,” he noted. “Well, where were the original carbonates?”
Ruff and a few colleagues did further research and published a paper in 2014 hypothesizing that the carbonates could have come from an evaporating, ephemeral lake or lakes recurring in Gusev. “The carbonate really is potentially consistent with an evaporative environment, maybe recurring multiple times that could have left carbonate behind in the rocks of Comanche,” he said. “It’s a reasonable hypothesis that responds to a set of observations made by both Spirit and from orbital instruments.”
Ruff has been rigorously challenged throughout the years. But he is driven. “I sometimes feel like a voice in the wilderness, but I will continue to pursue the science from Spirit, because it’s important and I want others to understand the richness of the dataset and what else we else we may be able to find,” he said. “Even though we quit acquiring observations in late 2010, for me this dataset is a gift that keeps on giving even well after the passing of Spirit,” Ruff continued. “Even now 14 years down the road, I can go back to Spirit’s observations and see new things and understand other things better.”
For a little more than a year, engineers tried repeatedly to get Spirit to respond to signals. They sent more than 1300 commands to the rover through the DSN’s X-band, and the ultra-high frequency (UHF) relay communications systems with Mars Odyssey and Mars Reconnaissance Orbiter, each an attempt to elicit a response from the rover. Each was met with radio silence.
On Monday, May 23, 2011, NASA and JPL officials announced the end of the official recovery effort. The last of the sequences prepared for a final intensified effort, were scheduled to be sent early May 25, 2011 PDT. "We always knew we would get to this point," noted MER Project Manager John Callas in May 2011. "We're here today because we wore Spirit out."
In six+ years of roving, Spirit drove 4.8 miles (7.73 kilometers), more than 12 times the goal set for the mission, chalked up a number of “firsts” along the way, and demonstrated a mechanical kind of MER mettle that set the bar high for future Mars rovers. "What's most remarkable to me about Spirit's mission is just how extensive her accomplishments became," said Squyres.
The MER team mourned Spirit and also properly celebrated all the rover had accomplished in a press-invite gathering at Caltech, and later with a more private Irish wake that was, as Fraeman reviewed it, “pretty awesome.”
Opportunity pressed on toward Endeavour. On May 19, 2010, she surpassed Viking 1 and became the longest-lived robot on the surface of Mars, with 2,245 sols and counting. And then, a little more than a year later on August 9, 2011, “Little Miss Perfect” reached Endeavour. It was a record-setting, mind-bending, rover-driving-wow of an achievement.
The rover made “land’ at Cape York, a remnant of Endeavour’s western rim, at an area with outcrop, a tiny crater, and a view inside the crater that the team christened Spirit Point. From there, Opportunity began a new mission, to travel farther back in Martian time than any other ‘bot ever to the Noachian Period some 3 to 4 billion years ago. It was during this epoch Endeavour was created, a time when planetary scientists generally believe Mars was more like Earth, with water flowing above and under ground, rivers winding, lakes pooling, maybe even an ocean, hot springs bubbling and volcanoes erupting.
“We had been anticipating it for so long and it took us so long to get there and we had so many challenges,” remembered Rover Planner Ashley Stroupe. “We never knew if we were really going to make it. Then, when we got that first view down into the crater – that for me is one of the absolute highlights from driving Opportunity. The only thing that will beat that day, that sol for me is if we get down to Iazu [Crater].”
For Arvidson the best moment was about a year away, waiting on a hill that was just on the other side of Cape York. The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), which searches for signs of past and present water on Mars from its perch on MRO, detected phyllosilicates, ancient clay minerals and a sure sign of past water, in the Cape York area. It’s why Opportunity and the team were at Cape York.
As a member of the CRISM team, Arvidson managed to acquire hyperspectral data that homed in on this particular hill as “the sweet spot.” The site was promptly named for Jake Matijevic, a brilliant and beloved member of the original Spirit and Opportunity development team and a former Chief of MER Rover Engineering. Jake had passed away unexpectedly in August 2012, the same month Opportunity was driving along the inner part of Cape York and nearing the base of the hill.
“I remember calling Steve and saying, ‘This is it, man. We’ve got to turn right and go uphill,’” Arvidson recalled.
Squyres agreed. The two handily convinced the last hold-outs on the science team during a SOWG meeting and Opportunity took that right turn. To say it was a good call would be a grand understatement. Turned out, Matijevic Hill is a science jackpot. The robot field geologist not only found evidence for ancient clay minerals but uncovered what the scientists believe is the most ancient Martian strata or ground ever discovered on the surface, now known as Matijevic Formation.
“To me that was the most exciting moment,” said Arvidson. “It was the confluence of a number of analyses that led to that right hand turn, including the CRISM multispectral map and what we could see with the Navcam looking uphill.”
Following her discoveries on Matijevic Hill, Opportunity headed onward in late spring 2013, driving through Botany Bay to another section of Endeavour’s rim dubbed Solander Point. From there, the rover continued south toward Cape Tribulation, imaging Murray Ridge, named for Bruce Murray, Planetary Society Co-Founder and former JPL Director in 2014, and various other geological features, before heading on to Marathon Valley, where CRISM picked up a mother lode of signatures for phyllosilicates.
On March 24, 2015, after spending several weeks investigating some new rock types along the western rim of Endeavour Crater, Opportunity, closing in on Marathon Valley, cruised past 42.2 kilometers (26.2 miles) to finish the first off-Earth marathon and drive the mission back into the space history books. "This is the first time any human enterprise has exceeded the distance of a marathon on the surface of another world," Callas announced in the NASA-JPL press release.
Working on Mars, however, was becoming challenging as Opportunity began suffering increasing ‘amnesia’ events, episodes when she failed to write or ‘save’ her science and telemetry data to her non-volatile, long-term memory or Flash drive. Worse, she had been experiencing sudden reboots or re-sets. The ops engineers had tried a number of things, eventually having the rover mask off one of Flash’s 8 data banks, confident it was corrupted and may be causing the problems. It didn’t work.
Out of options, the rover’s Flash was taken out of commission in May 2015 and Opportunity was configured to operate in RAM-only mode. Working in RAM, which is volatile memory, meant the rover would have to send each day’s work to the Mars Odyssey or MRO for downlinking to Earth before she shut down for the night or the data would not be saved or, in other words, gone. This mode would slow the pace of research but the team and its rover would adapt and persevere.
After checking out outcrops and a strange cairn-like stack of rocks named for aviation pioneer Charles A. Lindbergh just outside the entryway to Marathon Valley, the rover finally drove into Marathon Valley in July 2015. The rover spent a little more than a year conducting close-up studies of outcrops and rocks and soils, ultimately finding the phyllosilicates were everywhere, in the soils and rocks, ubiquitous but not obvious like they had been on Matijevic Hill.
In September 2016, Opportunity finally drove through the Lewis and Clark Gap and out of Marathon Valley, hiking farther down into Endeavour’s rim, toward the crater floor. The plan was for the rover to visit Spirit Mound, where the scientists were hoping to find more Matijevic Formation. They did not. It was Shoemaker breccia everywhere.
So in November 2016, Opportunity began what would be a four-month hike back up the crater rim. The rover was heading for an area where she could easily exit Cape Tribulation. Once on the other side of the rim, she would continue south on smoother terrain and make a bee-line to Perseverance Valley and Cape Byron.
When Opportunity reached the rim crest in March 2017, the team had her pause to take a parting shot of Cape Tribulation. It was promptly named the Rocheport Panorama. The rover then drove over the crest and cruised south along the flatter, smoother terrain, pulling up to the top of Perseverance in May 2017 and soon began a walkabout around the uppermost area of the valley.
A couple of months later, in June 2017 while finishing up work atop Perseverance, Opportunity ‘sprained an ankle.’ An actuator on her left front steering wheel stopped with the rover’s wheel toed out 33 degrees. After numerous attempts, working together the engineers and the robot got it straightened out. From that point on however, the rover would steer only with her rear wheel and drive like a tank.
Always willing, always workable, Opportunity drove into Perseverance backwards in July 2017 and, with a lot of help from her dedicated rover planners, is managing to navigate the slopes pretty well despite her new handicap. By the end of 2017, the rover was about half way down the length of Perseverance and is currently continuing research and her trek through the valley.
From the moments Spirit and Opportunity landed on Mars in January 2004, their reach was global and their inspiration beyond measure. Over the years, their cumulative scientific findings and engineering achievements have profoundly impacted planetary exploration, from discoveries that have informed our knowledge of Mars and rewritten textbooks to rover records that may stand for decades, a ginormous scientific pot of gold worth far more than the estimated $1 billion NASA has spent on the mission to date.
And for the humans, well…
“It has been the thrill of a lifetime to get to ‘live on Mars,’ virtually and vicariously, through the eyes of Spirit and Opportunity over all these years,” said Bell.
The original sense of wonder, gratitude, dedicated commitment, and brains-on-fire forward thinking that forged this now legendary mission still fuel the core of the MER ops team. By and large, these very human assets continue to resonate with and inspire every original MERster who has moved on to other things, as well as people everywhere around the world who have followed and come to know and love Spirit and Opportunity. Along with the phenomenal design and engineering and uncanny longevity of the rovers, these very human elements are why the MER mission is something truly special in the world of planetary exploration.
“I just feel lucky about being able to work on this amazing, special project,” said Stroupe, echoing the collective sentiments of the team. “I don’t think we’ll ever see the likes of this again.”
Mars is still the planet Earthlings love the most and its proximity and possibilities for human explorers give it the most drawing power. With Elon Musk’s Space X, as well as NASA aiming to send humans to the Red Planet, Mars, is as popular as it’s ever been. A lot of the current wanderlust is because of Spirit and Opportunity, because they have taken us there.
A picture is worth a thousand words, the saying goes, and the twin robot field geologists took pictures every rove of the way, over every Martian hill and every Martian dale, up every hill, and down every crater as they blazed humanity’s first trails up there. And Opportunity is still truckin’.
“Every year we have this conversation, and each year I’m incrementally more astonished than I was the year before,” said Squyres. “Incrementally, because I know what a good machine this is and I know what a good team is. If we’re fortunate and things go well, I’ll be a little more surprised this time next year,” he said, pausing. “It really is remarkable and it’s a joyful thing to continue to be part of.”
Deep Dive into January
Opportunity woke up to 2018 with 45.08 kilometers (28.01 miles) on her odometer and spent New Year’s Day Sol 4956 (January 1, 2018), recharging, just like many of her human colleagues on Earth.
Although the winter solstice came and went last November, winter still rules at Endeavour. The rover was producing a decent 420 watt-hours of power with a solar array dust factor of 0.663, meaning she was utilizing about 66% of the sunlight hitting her solar arrays. Overhead, the skies were slightly hazy with atmospheric opacity or Tau gauged to be around 0.483, about normal for winter.
Parked just ‘upstream’ of a fork in the primary trough or channel in Perseverance, Opportunity was waiting for her human colleagues to decide which fork she would take. The south fork featured some unusual looking rocks that were textured and streaked and within easy reach. The north fork offered a richer bounty of geological features, including more of the intriguingly textured outcrops. “But every rock we see is of interest to somebody,” reminded Arvidson.
As Opportunity took images of one of those intriguingly textured outcrops on the north edge of the north fork, the team named San Miguel and came to a decision. On Sol 4958 (January 3, 2018), the robot put it into gear and drove just 4 meters (13.12 feet) down the uncharted path of the north fork. “When we encounter one of these rocks that we can approach relatively easily, we’ll likely do APXS and MI, but in the meantime, the rover is focusing mainly Pancam and Navcam imaging to characterize the colors the spectra and the morphology and the topography of the valley from this site,” Arvidson said.
The robot geologist spent most of the rest of the first week in January taking images, though on Sol 4961 (January 6, 2018) used her Alpha Particle X-ray Spectrometer (APXS) to check out a target of opportunity within reach.
Meanwhile, JPL engineers prepared and executed a test of the Zero Degree Heater (ZDH) on the batteries, as Chief of MER Engineering Bill Nelson discussed in the September 2017 issue of The MER Update. Opportunity carries two 8-amp-hour lithium batteries, which she reenergizes with the solar power she produces. [During the rovers' prime missions, their solar arrays were able to produce around 900 watt-hours of energy per Martian day, or sol.]
While Opportunity's batteries have performed exceptionally well over the mission's lifetime, 14 years is – well, 14 years, and they are beginning to show some signs of aging. Though the rover has never once used the ZDH (amazing but true), it was designed specifically to warm the batteries. Since the Martian environment is so brutally cold, the theory for at long last deploying the ZDH is that warming the batteries during the recharge process may make the batteries both more effective and help them degrade slower.
The team wanted to be cautious before using the ZDH operationally and formulated a plan to test it. The first original test in this campaign was to turn on the heater briefly, manually as opposed to thermostatically, and in a controlled and recoverable setting, just in case of a fault. Opportunity executed the test in the morning of Sol 4964 (January 10, 2018), and from all appearances, it was successful.
During the second week of January, Opportunity spent several sols completing stereo, color panoramas, taking some targeted 13-filter images, and capturing some twilight images of the stone stripes the robot has been seeing in this part of Perseverance. Then she got her roving orders.
On Sol 4968 (January 14, 2018), the rover headed 6.97 meters (22.88 feet) farther into the north fork to try and reach some of the intriguingly textured rocks for closer investigation. She also imaged another of the intriguing textured outcrop rocks along the edge of the north fork, which the team named Ojo del Muerto. It looked like San Miguel and the team was starting to see a lot of them in this part of the valley. The next sol, the ‘bot took a day to recharge.
“We had seen in the previous remote sensing data was that these rocks appeared slightly different from the standard Shoemaker impact breccias,” said Golombek. “There were also some color differences to suggest they may be new and different rock types. The rock is very bumpy and has this lineated surface texture, which may be erosion caused by wind or sand or something else. But it doesn’t look the same as typical Shoemaker type rocks, so we’re taking a whole bunch of MIs to try and get some coverage to see what it is.”
And then, on Sol 4970 (January 16, 2018), the rover’s power portfolio began to really change as a series of dust gusters whipped up from Endeavour’s floor and whisked a good amount of accumulated dust from the rover’s solar arrays. “It’s not surprising,” said Arvidson. “The winds are supposed to be blowing up and out of this valley from the crater floor.”
The wind events sent the rover’s energy production up substantially. “We had a big jump on that sol,” confirmed Herman. “We went from a dust factor of about 0.68% to 0.76%, a jump of 0.08%. That is really a sizeable jump. Normally, with the dust cleaning events, it will just go up 0.01 or 0.02%, not 0.08%. The energy was 517 watt-hours,” said Herman.
The next sol, 4971, the rover’s dust factor improved by another 0.04% and on Sol 4972, it jumped another 0.02%, taking the dust factor up to 0.82% with power rising to 565 watt-hours. Then on Sol 4974, another cleaning event improved it by another 0.02%, taking the dust factor up to 0.84% and Opportunity’s power to 599 watt-hours. And as the month progressed, it would improve even more.
The robot spent the third and part of the fourth week of January taking color images of light toned bedrock and more of the textured and streaked rocks. She also worked in an APXS argon measurement for the mission-long study on Sol 4974 (January 20, 2018).
Opportunity homed in on a textured rock the team named Jornada del Muerto, which, again, looked like the San Miguel outcrop rocks. Although the research on these distinctive new rocks had just begun, the scientists were beginning to refer to identify them as San Miguel class. On Sol 4975 (January 21, 2018), the rover bumped for 1.32 meters (4.35 feet) to put Jornada del Muerto in reach of her IDD or robotic arm so she could examine it up close.
The robot field geologist then examined the rock using the routine science protocol, taking the MI pictures needed for a mosaic of the target spot on Sol 4977 (January 23, 2018), and then placing her APXS on the target.
Opportunity continued her work on Jornada del Muerto during the final week of the month. On Sols 4984 and 4985 (January 30, 31, 2018), she took more MI's and APXS integrations after off-setting the instruments just a skosh from the previous target spot on the rock to look at it again. The rover was also slated to take more color Pancam images of the margins and areas around the north fork and of her immediate surroundings.
The winds continued to whisk dust from the rover’s arrays as January wound down. Opportunity, with 45.09 kilometers (28.02 miles) on her odometer, was producing as much as 644 watt-hours of power, with a dust factor of 0.839. The Tau improved to around 0.423. “We did drive and get a better tilt towards the north where the Sun is this time of year,” said Herman. “Changing our tilt to more than 9 degrees really helped, especially because the sky is so clear so having direct sunlight was really useful.”
At the same time, Perseverance Valley is proving to be “complicated,” Arvidson said. “There are things that are becoming clear and we’re still puzzling about other things. For example, we’ve talked about wind etching of the rocks, the wind blowing up hill and these little wind tails in the rocks. What’s also becoming clear is that there’s a lot of regolith in the troughs and it is slowly marching downhill, down the valley, and is building up against the uphill sides of outcrops. In addition, it’s being shaped during its downhill march into stone stripes. Whether the stone stripes are due to wind, mass movement, or freezing and thawing of water in some previous epoch remains to be seen, but they are a surprising, unique morphology we haven’t seen anywhere else.”
At the halfway mark in the trek through Perseverance, neither rover nor science team members have seen a glimpse of Matijevic Formation, the oldest Martian terrain, and they are still doing the research to determine what carved the valley billions of year ago. But the research Opportunity is doing now is scientifically significant and will add to the story of water at Endeavour billions of years ago. “It points out that Perseverance Valley has unique features, in its overall shape, in the amount of regolith piling against the uphill sides of outcrops, and in terms of turning the regolith morphologically on the surface into these stone stripes,” said Arvidson.
In coming sols, Opportunity will continue working her way down the valley, said Golombek. “We’re not in any super rush here and we want to do it right.”
Opportunity and the team are powered up and ready to rove and rock.
“Our rover is now 14, which is 98 years in dog years, so I am always amazed about what she is still capable of doing,” said Bellutta. “In the short term, I am looking forward to completing the drive through the north fork. From HiRISE images, it looks quite challenging and interesting. In the long term, I think I want to see Endeavour from the bottom. I want to look back at the Valley and all the tracks we left. But among all things, I'm looking forward to year 16 and 17...and 18...”