With the Martian winter on the run at Endeavour Crater, the Mars Exploration Rovers (MER) mission cruised closer to its 14th anniversary of exploring the Red Planet in December as Opportunity deliberated a distinctive “fork in the road” deep in Perseverance Valley and wrapped another record year.
A glimpse into 2018
NASA / JPL-Caltech / Cornell / ASU
A GLIMPSE INTO 2018
From the gentle slope in Perseverance Valley where Opportunity spent the 2017 holiday season, the robot captured these frames with her Panoramic Camera (Pancam), and the Pancam team processed them in false color. They show a part of her panoramic view of the ‘fork in the road’ or bifurcation, the point where the large trough or channel in the valley splits into two forks. “This is a braided channel and it divides and it comes back together and we’re at one of the divides,” said MER Principal Investigator Steve Squyres as December came to a close.
Every year Opportunity has been exploring Mars has been one of challenges and rewards and 2017 was no exception, except perhaps it was more intense than most. The veteran robot field geologist was scaling the steep, sometimes slippery-with-gravel slopes of Cape Tribulation on her way to the valley when the year began. Now, as 2017 comes to an end, the robot field geologist is deep inside Perseverance and deep into the mission’s research, the centerpiece of the team’s tenth extended mission, looking to go farther back in Martian geologic time and uncover buried scientific treasure.
It hasn’t exactly been a walk in the park. “From Spirit Mound and up to the rim and then back down Perseverance Valley, the topographic profile from 2017 is on a par with what we did with Spirit when we climbed Husband Hill back in 2005,” MER Principal Investigator Steve Squyres, of Cornell University, reflected as December came to an end. “We did the most challenging, difficult driving over some of the most rugged terrain we’ve ever done with this vehicle all these years in.”
Years indeed. On January 24th, 2018, the MER team and Opportunity will complete their 14th Earth year of surface operations on the Red Planet, and then begin the 15th year of this adventure, NASA’s first overland expedition across Mars. “And the rover is still going strong and still doing great science,” said Squyres.
In fact, Opportunity is going where no robot on Mars has gone before. “Perseverance Valley is a truly enigmatic feature that is unlike anything we’ve ever seen on Mars or been able to drive to and across,” said Deputy Principal Investigator Ray Arvidson, of Washington University St. Louis. “The work we do here will be the first ground-based exploration of a preserved valley system on Mars. It’s like another new mission.”
Cutting west to east and forming a broad notch in the remnants of the crater’s western rim at Cape Byron, Perseverance stretches downhill for the length of about two American football fields (about 220 meters or around 720 feet), at a slope of about 15 to 17 degrees, all the way to the floor of the crater.
Positioned on a north-facing slope in the valley’s south wall where she could angle herself toward the Sun and soak up the winter Sun, Opportunity spent the month of December imaging at a couple of different sites about halfway down the length of the valley. Her sights and her camera lenses were primarily focused just downhill where a large trough or channel splits into two paths and creates a ‘fork in the road.’
“This is a braided channel and it divides and it comes back together,” said Squyres. “We stopped at one of the divides here for the Christmas holidays and to take a break for a while.”
The first time the MER scientists saw the orbital images of Perseverance they generally thought it had been carved by water, flowing water or melting ice or maybe a muddy debris flow. Other theories suggest the Martian winds or perhaps a dry debris flow might have chiseled the valley, and still others suggest some combination of these forces. But the water theories keep rising to the surface. The veteran Mars explorer and the MER team are here to figure it out.
Perseverance or bust
NASA / JPL-Caltech / Cornell / ASU / J. Sorenson
PERSEVERANCE OR BUST
Opportunity acquired the Pancam frames for the Rocheport Panorama, above, from just inside edge of the western rim of Endeavour Crater at Cape Tribulation in February 2017. After taking this parting shot, the rover climbed up and over the rim crest and drove caddy corner, off into the sunset on this image. This version of Rocheport was processed by James Sorenson in near “true color.”
Endeavour Crater dates to the Noachian Period, some 3 to 4 billion years ago when scientists believe Mars was warmer and wetter and more like Earth and Opportunity is the only rover, MER the only mission on the Red Planet, to have ever traveled this far back in geological time. Uncovering evidence of past water, of course, is exactly what NASA created and dispatched Opportunity and her twin, Spirit, to do, in the space agency’s ‘Follow the Water’ Mars exploration campaign.
Opportunity found the mission’s first ‘hard’ evidence of Noachian Mars at Cape York on Matijevic Hill in 2012–13. Discoveries there included the oldest strata found to date, the Martian ground when the impact that created Endeavour hit the surface (Matijevic Formation); remnants of ancient clay minerals, an indisputable sign that water was once here; and another never-before-uncovered ancient rock layer (Grasberg), which the MER scientists think formed after the impact.
The MER scientists are optimistic that Opportunity will journey again to that time during the Noachian Period and find the evidence needed to describe the environment here all those years ago – and how exactly the unique geological feature forever now known as Perseverance formed.
For as much progress as Opportunity made in 2017, the year was not without some significant challenges. Opportunity’s left front wheel, for one, was pulled out of steering commission in June and the rover has since steered with her rear wheels and turned like a tank. But with the ‘curses’ of exploration, there were ‘blessings.’
As steep as the slopes are, the ground beneath the rover’s wheels has been decent. “I was expecting a tougher terrain to traverse,” said Rover Planner Paolo Bellutta, the rover robotics expert who oversees the charting of Opportunity’s routes from his post at the Jet Propulsion Laboratory (JPL), where all of NASA’s Mars rovers were ‘born.’ “The loss of front steering capability does not help, but it is not a limitation that I feel is hindering the mission,” he said. “So far, most of our troubles are the consequence of driving on steep slopes.”
Steep slopes and rover aches and pains considered – along with the fact that this is Mars – the MER mission team and Opportunity will be entering their 168th month and 15th Earth year of roving Mars in pretty fine form. “This rover is a real trooper,” summed up Chief of MER Engineering Bill Nelson, of JPL. “Opportunity continues to do everything we ask and perform as we expect, and continues to amaze us with its longevity.”
When you consider that back in the beginning the team members thought they might have a year, one year outside to explore Mars with the MERs, Opportunity’s longevity is beyond astounding. The legendary success of this mission didn’t just happen though, like some kind of happy accident.
Rather, it is a kind of perfect storm of excellence, and testimony to the engineers who built Spirit and Opportunity, to every person who worked for every company that manufactured an instrument or a piece or part, to the Entry, Descent and Landing team that got them safely to the surface, to each of the scientists who lead and conduct the investigations, to the engineers who tend to the rover and craft workaround ‘miracles’ to get her where the scientists want her to go, and to the ops team at large, the dedicated people who countless times have given up weekends or holidays to care for this robot. That, all of that, is what has driven this mission to become a legend in its own time and kept Opportunity roving day in and day out.
“And it’s also an indicator of how interesting a place Mars really is,” reflected Squyres. “It’s a combination of all those. We wouldn’t keep making new discoveries if Mars didn’t keep throwing new things at us. But Mars does.”
As 2018 dawns on Earth and on Mars, optimism and gratitude continue to power the human core of the MER mission and the team’s mantra remains the same: every day on Mars is a gift.
On the road to Perseverance
NASA / JPL-Caltech / Cornell / ASU
ON THE ROAD TO PERSEVERANCE
Opportunity used her Pancam to take this image of her tracks on April 20, 2017. The Pancam team processed this version in false color, a technique that enables scientists to better discern the different elements in the often-monotone, rusty redness of Mars.
2017 in Review
When January 2017 rang in at Endeavour Crater it was summer and Opportunity was hunkered down on a slope inside the rim at Cape Tribulation just to the north of Beacon Rock, waiting patiently for the holiday celebrations on Earth to end. The rover in November 2016 2016 had departed Spirit Mound, the first planned science stop on the MER’s tenth extended mission located deep in the rim near the crater floor, and spent the winter holidays taking a break from hiking up the steep slopes toward the rim crest.
Although the rover was designed to navigate 15-degree slopes, Opportunity was regularly hiking slopes that average around 20-degrees and more. The going was tough. The steep slopes, ragged terrain, a blinding summer Sun, and the rim wall to the west that blocked her communications conspired to slow her pace. "We're trying to get to our egress point so we can get onto the flatter terrain of the Meridiani Plains that surround the rim and make some good progress down to Cape Byron and the valley," explained then-MER Lead Flight Director and Rover Planner Mike Seibert, of JPL.
The robot field geologist had been struggling to get around a large landmark boulder the team named Beacon Rock. The initial plan had been to go around it to the east and through Willamette Valley, and then up to the crest of the rim. But the gravelly slopes and loose terrain were foreboding, so as 2017 got underway the team redirected the rover. The march uphill continued with a revised route, taking the robot to the north and west of the giant rock.
Opportunity route maps
NASA / JPL-Caltech / Malin Space Science Systems / UA / P. Stooke
OPPORTUNITY ROUTE MAPS
The orbital image of the western rim of Endeavour Crater [left] shows the path Opportunity took from Cape Tribulation to Perseverance Valley, which the robot is currently exploring. The map on the right shows the rover’s movements up to Dec. 10, 2017, her location through the end of the year. Phil Stooke, Assoc. Professor at the University of Western Ontario, Canada, and author of The International Atlas of Mars Exploration Volumes 1 and 2, (Cambridge University Press), meticulously documented this graphic with sol and site annotations. The base images were taken by the Context Camera [left] and the HiRISE camera [right] both onboard MRO.
On Sol 4623 (January 24, 2017) Opportunity celebrated her 13th birthday climbing west/southwest up another slope to finally put Beacon Rock in the rear-view mirror. From there, the rover continued to push upslope, heading south and west through Cape Tribulation toward the rim.
Opportunity finally reached the crest in February. There, the robot field geologist looked around with her Panoramic Camera (Pancam) ‘eyes’ and took in the views. “This is it for Cape Tribulation and so we stopped short of going over the crest to acquire a good, parting shot.” Arvidson.
From here, the rover would take an “express route” to Cape Byron and Perseverance, about a half-mile away. Driving caddy corner down the outboard side of the crater rim to the southern part of Cape Tribulation, the rover would then scoot onto the flatter Meridiani Plains terrain that lays in between the capes to fast-track her trek. Once Opportunity arrived at Cape Byron, she would climb back up, over, and into the west rim to enter Perseverance Valley.
Opportunity was about to hit the road when the scientists saw something in the rover’s images that was too intriguing to pass up. “We were about to exit the ‘door,’ but suddenly we discovered this ‘door’ is pretty exciting,” said MER Project Manager John Callas, of JPL.
So, while completing the Rocheport Panorama, named for the town along the Missouri River that Lewis and Clark and crew passed through in 1804, the robot geologist conducted one last scientific campaign at the rim crest. It was on an outcrop of finely striated bedrock that looks to have been etched or carved by something. “We decided to take some detailed Pancam imaging of the area and are still debating whether the geomorphic expressions, the striations were formed by wind or ice or something else that occurred during the impact,” said MER Deputy Project Scientist Abby Fraeman, who first worked on the mission in 2004 while still a high school student and one of The Planetary Society’s Red Rover Student Astronauts.
It turned out to be more of the same breccia bedrock that Opportunity has been roving on and around since pulling up to the crater’s western rim in August 2011: rocks and outcrops formed during the impact that created the 22-kilometer (about 13.7-mile) diameter Endeavour, now known as Shoemaker Formation. The team has yet to come to a consensus on what caused the etchings.
Martian summers routinely generate rover-threatening dust storms, but Opportunity was lucky enough to work under “storm free skies” throughout the month of February despite a large regional storm about 500 kilometers away. “We can actually see [the storm] in the distance in one of the Navcam panoramas,” said Callas. “This is the first time we've actually seen one of these dust storms from the ground. By month’s end, the threat has passed, but the dust that was falling out was hazing the skies over Endeavour and dampening the rover’s power. “We're keeping our eyes on it.”
As luck would have it, the storm’s winds, along with the dust, sent some gentle gusts blowing eastward to Endeavour, which conveniently cleared off some of the accumulated dust from Opportunity’s solar arrays, translating to a boost in the rover’s power. Just as the February storm began to dissipate however, another regional storm followed in its dusty wake during the first sols of March, causing concern and ensuring that dust would continue to command the skies for weeks to come.
Moonshot
NASA / JPL-Caltech / Cornell / ASU / Texas A&M
MOONSHOT
During the afternoon of May 5, 2017, shortly after pulling up to the top of Perseverance Valley, Opportunity looked to the sky with her Panoramic Camera “eyes” hoping to capture an image of the Martian moon Phobos as it raced by the Sun. With a little help from MER Science Team member Mark Lemmon, at 14:59 hybrid local solar time (HLST), the rover pushed camera “shutter” – and nailed it.
Undaunted, Opportunity finished the final science investigations on the slopes of Cape Tribulation, then climbed up and over the crest of Endeavour to the other side of the rim, to embark on the journey south toward the valley. “Right now we are in the business of making wheel tracks and that's what we're going to be doing until we get to Perseverance Valley,” said Squyres.
The MER mission’s lucky star kept shining on Opportunity throughout the summer of 2017. Despite a prediction from NASA-JPL that 2017 may bring a planet-circling storm that would put the Red Planet in the black, the rover successfully dodged two, potentially deadly dust bullets.
Opportunity didn’t completely escape the storm’s wrath. Dust from those regional storms continued to rain steadily on Opportunity throughout March. “The dust cleaning events didn't stick,” reported MER Power Team Lead Jennifer Herman, of JPL. “We're dirtier now than we were before the storms.”
At the same time, the rolling, distance-blocking topography challenged the veteran rover, “limiting drives to around 15 to 30 meters,” said Bellutta. That’s roughly between just 50 and 100 feet. “But we are making good progress,” he said.
Indeed. Perseverance was absolutely, positively, and magnificently within reach and no one was betting against this rover.
Opportunity was scheduled to spend her first sol in April taking images of a light-toned mesa in the distance that the team christened Winnemucca. Past that, the plan for April was “Drive, drive, drive.” as Arvidson put it.
While the robot cruised outside the western rim along the flatter, plains terrain, fall was blowing in and the thick, dusty haze in the skies from the regional storms of February and March was slowly thinning. The Tau hung around 0.981. And although the rover’s dust factor had decreased to 0.597 as fallout from the storms rained down, Opportunity was producing a respectable amount of power, upwards of 400 watt-hours.
The veteran rover worked hard to pick up the pace, logging 10 drives and covering about a quarter of a mile in April, closing in on Perseverance Valley. On one drive, Opportunity sprinted for more than 130 meters (about 430 feet) in a dash the likes of which she hadn’t done probably since leaving Cape York about four years ago. It made drivers on Curiosity duty a little, well, envious.
“We’ve been making astonishing progress,” said MER Rover Planner Ashley Stroupe, of JPL. “It’s been much easier to drive on the smoother terrain.” Opportunity was now within striking distance.
Along the way, the robot managed to work in a few science investigations. One outcrop puzzled the science team. It was bedrock with a somewhat familiar composition, but one that did not neatly match any strata the mission has found so far. “Mars still surprises us,” said Arvidson. The robot found no signs of the ancient Matijevic Formation outcrops.
On May 4, 2017, the rover’s 4,720th day on Mars, Opportunity, at long last, drove into the entryway or the top of Perseverance Valley. “We’ve proved through lots of perseverance that we could make it and we have arrived,” announced Squyres. “It’s so new and so different. And it’s really, really cool.”
It was an unparalleled achievement. Imaging the views all around with her Pancam and Navcam, the rover took it in, and then set out on a walkabout. As for the view: “It’s nice and flat,” said Callas. “And all of the sudden, it just disappears over the edge.”
Sprained Ankle Pan
NASA / JPL-Caltech / Cornell / ASU
SPRAINED ANKLE PAN
Toward the right side of this portion of the Sprained Ankle Panorama is a broad notch in the crest of the western rim of Endeavour Crater that leads down into Perseverance Valley. You can see tracks that Opportunity left as she roved on a walkabout of this area atop the valley in May and June 2017. Perseverance, the prime destination for the rover's extended mission, descends out of sight on the inner slope of the rim, extending down from that notch and eastward toward the crater floor. Opportunity took the component images for this view with her Pancam in June 2017. This image was processed by the Pancam team in true color.
The fall equinox fell on the day after Opportunity pulled atop Perseverance, May 5th, the same sol that marked the start of the MER mission’s eighth Mars year, and the same sol that the mission team hit the pause button so the rover could shoot the Moon. Looking skyward with her Pancam at specifically chosen times, the robot aimed to freeze frame the fast-moving Martian moon Phobos as it transited the Sun.
“You’ve got to be taking pictures in the right place at exactly the right time,” said Mark Lemmon, an associate professor in the Department of Atmospheric Science at Texas A&M University, MER science team member, and “the brains behind the effort,” as Planetary Society President Jim Bell, the science lead on the rovers’ Pancams, defined him.
With extreme precision in the planning, Opportunity got the Moonshot. Then, the ‘bot promptly got back to checking out targets atop the valley, looking for any kind of evidence that may indicate how this distinctive valley formed as she shot images of all she could over the crest and into the valley. The images were scientific data, but they also would serve as navigation data for the rover planners to determine with certainty that the rover will be able negotiate the downward hike into Perseverance.
During the walkabout, the scientists looked through their rover’s “eyes” for telltale signs of water or wind or ice or any weird Martian thing. “In contrast to many walkabouts we have done in the past, this walkabout is all about geomorphology, the landforms,” said Squyres. That meant Opportunity would shoot “lots and lots and lots of high-resolution stereo Pancam imaging.”
Opportunity may have been dustier than last winter but true to her MER mettle, but the rover accommodated all commands and kept on truckin’ on her walkabout atop Perseverance in June. Among other geological things, Opportunity imaged a large, shallow channel or trough with “a pattern of striations running east-west outside” the crest of the rim. It might have been a drainage channel or spillway billions of years ago—or not. “We want to determine whether these are rocks that have been transported here or are in-place rocks," Arvidson said.
The scientists debated the possibility that this site was the end of a catchment, where a lake was perched against the outside of the crater rim. Could “a flood could have brought in the rocks, breached the rim, and overflowed into the crater, carving the valley down the inner side of the rim?” asked Arvidson.
If that were the real scenario, the notch in the crater rim crest leading into the valley would have been a water spillway. Weighing against that hypothesis however were the rover’s images that show the ground west of the crest slopes away, not toward the crater. The team would later determine there was most likely no lake here.
The autumn skies over Endeavour Crater remained hazy as dust from the summer storms continued to rain down, but Opportunity remained productive during her walkabout atop Perseverance, capturing image after image with her cameras visually documenting the area. Then June brought a ‘gloom’ that cast a pall on the mission team. While Opportunity making a basic arc back maneuver to turn, the steering actuator for her left front wheel stalled and she stopped, with that wheel stuck, toed-out 33 degrees.
More than 12-and-a-half years before, in April 2005, the steering actuator for Opportunity’s right front wheel jammed and stuck in a toed-in position of about 8 degrees and she has driven with it like that ever since. But 33 degrees toed out?
During the ensuing sols, Opportunity followed commands to see if the wheels had caught on anything. The rover’s images of the scene however ruled out terrain or small rocks as the cause. In the mix of all this movement though the robot scuffed up a small patch of crumbly white soils. Laramie, as the team named it, hints of past water. But there was no time to check it out up close.
Laramie
NASA / JPL-Caltech / Cornell / ASU
LARAMIE
After Opportunity’s left front steering wheel jammed in June 2017, she backed up so the MER ops engineers could see if the terrain has caused the wheel to jam. While the terrain was ruled out as the cause, a small patch of crumply white materials appeared. Named after one of the stops on the First Trans Continental Railroad route, Laramie hints of past water, but there was no time to check it out up close.
The Earth-Mars solar conjunction was coming up in July and the mission’s eighth Martian winter would set in soon after. With the stuck left front wheel, there was an increased desire to get into Perseverance Valley as soon as possible and the team’s attentions turned to roving on.
Even so, Opportunity had returned some familiar Pancam spectra, and Bill Farrand, Senior Research Scientist at the Space Science Institute in Boulder, Colorado and a member of the MER science team, considered it “plausible” that the stuff could be “some kind of hydrated sulfate mineral.” The data was similar to the spectra from the “jelly donut” rock Pinnacle Island and Stuart Island that the rover found back in January 2014, farther north on the rim, just in time for her 10th anniversary.
After a series of tests and unsuccessful straightening attempts, ops engineers decided to try one more thing. Voila! On June 17th, the rover straightened her left front wheel. “It was miraculous,” said Squyres.
When the telemetry that confirmed the rover’s wheels were all straight arrived on Earth, it was a Father’s Day gift like no other for the thousands of “fathers” who helped put Opportunity and Spirit on the Red Planet and got them roving along on NASA’s first overland expedition of Mars. “The MER team experienced an exciting two weeks, but it ended with relief and joy,” said Fraeman. “Once again, the rover amazed us.”
Everyone, especially the rover handlers knew this incident could be an omen. They decided from this point onward, the veteran rover would drive in a cautionary mode. "For at least the immediate future, we don't plan to use either front wheel for steering," announced Callas. “We’ll steer with our rear wheels,” said Nelson. “And turn like a tank.”
Opportunity and the rover planners adapted quickly and the mission was soon back to work, looking for clues and finishing her imaging assignments of the rock piles along the edges of the trough or channel, as well as various rock groupings.
Bellutta, meanwhile, had worked with the drivers and the scientists to chart the first of three planned drives back toward the rim crest and into Perseverance Valley. “We’re aiming for a nice cozy spot with about 10 degrees northerly tilt,” he said.
On July 6, 2017, Opportunity’s Sol 4781, the rover drove 13.4 meters (43.96 feet) and over the rim’s edge, venturing confidently yet cautiously into Perseverance and made it look easy. After so many years, so many miles, so much effort, the mission scored a major hit. It was a stellar achievement in the annals of planetary exploration.
“Perseverance has been calling us for years,” said Squyres. “Exploring the valley is the next big science phase of the mission. This is just tremendously exciting.”
