The Mars Exploration Rovers team and colleagues at NASA’s Deep Space Network (DSN) continued reaching out and listening for Opportunity throughout December, but all they heard was the sound of silence, again. It’s now been more than six and a half months that the longest-lived robot on another planet has been incommunicado.
After Opportunity sent a downlink June 10th, the “mother of all dust storms,” as some team members have described it, blotted out the Sun and stopped the solar-powered rover and the MER mission in their tracks. Shortly thereafter, the robot presumably shut down and went into a kind of hibernation as the massive storm pummeled Endeavour and then blustered its way around the planet.
Since then, DSN engineers have sent out more than 448 recovery commands and gotten not so much as one ‘beep’ back.
“Hopes remain high, the team remains vigilant, and we’re going to keep trying,” MER Principal Investigator Steve Squyres, of Cornell University, told The MER Update not long before the New Year rang in. “Opportunity is a tough rover and has pulled through a lot of tough things before. We’ll see what happens.”
As it stands now, NASA officials will consider the ops team’s next recommendation and reassess recovery efforts at some point in January.
Given the intensity of what would become the worst planet-encircling dust event (PEDE) in decades, there is a possibility that maybe the rover doesn’t have quite enough energy to wake up and send a downlink, or for other reasons may need a little coaxing. During the last several months, mission operations team members and the DSN crew have increased their "sweep-and-beeps," a procedure wherein they use the massive DSN antennas to scan the spectrum of X-band radio waves, try to find and lock onto Opportunity’s frequency, and then ‘ping’ or electronically nudge her to respond.
Mission teams communicate with spacecraft at and on Mars on X-band radio waves, which propagate at much higher frequencies than radio waves used for, say, FM radio stations. Like every Mars spacecraft, Opportunity has her own frequency.
In their search for any signal the intrepid little robot might have sent homeward, engineers and scientists have been alternating their communicative efforts during the last four months between the two wave configurations of Opportunity’s frequency, defined as the right-hand circular polarization and left-hand circular polarization.
Although the rover normally communicates on the right-hand circular polarization of the wave, the assumed mission clock fault was programmed to shift her outreach efforts to the left-hand polarization. Also, the robot could be in a scenario where she is alternating between the two wave configurations, so the team is considering the possibilities.
In addition to expanding these “sweep-and-beeps,” the MER team and their DSN colleagues have also been keeping an ear out during the rover's daylight hours listening for Opportunity over a broader range of times and frequencies picked up by the network’s highly sensitive Radio Science Receivers, said JPL’s Chief of MER Engineering Bill Nelson. Because these receivers detect and record all signals emanating from Mars, radio science personnel at the Jet Propulsion Laboratory (JPL), where all NASA’s Mars rovers were designed and built, along with a MER flight director or mission manager can carefully search the recorded data for the rover's signal the next morning.
Summer continues to shine on Endeavour Crater and Opportunity’s site in Perseverance Valley. That means it’s still dust storm season. The good news is that no new threatening storm popped up in December and the dusty haze lingering in the sky over the 22-kilometer (13.7 mile) diameter crater was estimated as “about normal” for this time of year. The bad news is that the seasonal cycle of winds tucked within the greater dust storm season – which historically have served to clear accumulated dust on the rover’s solar arrays – either haven’t arrived in Perseverance or haven’t cleared enough dust from the rover’s solar arrays or something else has happened.
For now, it remains a waiting game.“There’s just no new news on Opportunity,” said MER Deputy Principal Investigator Ray Arvidson, of Washington University St. Louis.
Nevertheless, the MER science team continued working, developing next papers, as well as thinking about what’s next for the rover, as reported in the last issue of The MER Update. Arvidson and various science team members also contributed to 12th mission extension proposal that Squyres and MER Project Manager John Callas will submit to NASA Headquarters in February 2019. This plan would have Opportunity complete research in Perseverance Valley, and then rove down into the crater, and beyond.
One thing is certain: the golf-cart-size ‘bot is still there. Though Martian winds are not like Earth winds and don’t have the force in that environment to knock Opportunity off her wheels, confirmation arrived in images taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter (MRO). Still, the orbital images aren’t close enough or sharp enough to even suggest how dusty the rover is, and until she phones home or the team makes contact, there is just no way of knowing her status or if she is capable of recovery.
Opportunity spent the first half of 2018 roving around and checking out the rocks and imaging the morphology or shape of the central part of Perseverance Valley. This research is a big deal. It is the first ground-based study of a carved valley on Mars and also represents the first exploration of rim segments of a large, ancient crater anywhere in the solar system. “We don’t have a crater that has preserved a rim of this scale on the Earth,” noted MER Athena Science Team member Larry Crumpler, of the University of New Mexico and the New Mexico Museum of Natural History and Science.
The robot field geologist first entered the valley in July 2017 to search for signs of anything in the morphology that would reveal how it formed. Situated within the Cape Byron segment Endeavour Crater’s west rim, Perseverance extends downslope for about 200 meters (about 219 yards) at about a 15-degree angle, and ends at the crater interior. From orbital images, it looks like a river system, with branches extending in different directions.
As enticing as that is, from the outset the science team was adamant in its pursuit of testing multiple working hypotheses to determine how this unique formation came to be. But the valley is old, two billion years or so old, so determining its origin has been no small or easy task. The team dream now is to recover the rover, chalk up another engineering ‘miracle’ and finish the research in the only geologic formation of its kind in the rim segments of Endeavour
More than ever before, time is of the essence. The fall equinox in the southern hemisphere of Mars is coming up on March 23, 2019. The winter solstice will follow October 8, 2019 and put the rover in the ‘deep freeze’ of the harsh season. Nighttime temperatures during winter can drop to -96 degrees Celsius (-140 degrees Fahrenheit). Brutal temperatures like these are believed, in part at least, to have resulted in the loss of Spirit back in 2010.
Since Opportunity has experienced a low-power fault, a mission clock fault, and an up-loss timer fault, the ops engineers know that it will take several weeks or more for them to recover Opportunity once they hear from her, if they do. Each of these faults must be addressed before there is a chance for the rover to rove on, and the team is prepared and at the ready. Other than that, they can’t do anything until they make contact.
Meanwhile, the MER ops engineers have been contemplating a few “Hail Mary” commanding strategies, “ways to try and force the rover to talk with us, if we haven’t heard anything,” said Spacecraft Systems Engineer-Flight Director Michael Staab, who has been working for months on various aspects of the mission’s recovery strategy. These would be “last ditch” efforts. Given that the team is not communicating at all with Opportunity however, the decision to ‘blind command’ one or more of these Hail Mary’s would likely only be made with the approval from the Mars Exploration Directorate at JPL and, of course, NASA Headquarters.
There is another possibility. Maybe something else unknowable has happened and the rover that shattered virtually every robot record on Mars simply can’t phone home. There are numerous single string components that went into making Opportunity and a break in any of them would be mission catastrophic.
But at this point, the fact is – no one knows anything about the status and health of the beloved rover, and no one on the team is giving up yet.
Looking back on 2018
Opportunity woke up to 2018 just ‘upstream’ or west of a fork in the primary trough or channel that defines Perseverance Valley.
The robot had 45.08 kilometers (28.01 miles) on her odometer and was braving the way below freezing temperatures of the mission’s eighth Martian winter. The skies were slightly hazy with the atmospheric opacity or Tau, the measurement of the amount of dust or opacity of the Martian sky was estimated around 0.483, the lower end of the range for the harsh season.
Opportunity’s solar array dust factor was estimated at 0.663, meaning the solar-powered rover was utilizing about 66% of the sunlight hitting her solar arrays to produce energy a decent 420 watt-hours of energy.
The robot spent her first Martian days or sols of the year completing color panoramas, capturing some twilight images of stone stripes the team had been seeing in this part of Perseverance, taking targeted images named for stops along the El Camino Real de Tierra Adentro, the old, 2,560-kilometer (about 1,591-mile) trade route between Mexico City and San Juan Pueblo, New Mexico, and waiting for her human colleagues to decide which fork she would take.
The roving orders came soon enough and Opportunity ventured into the north fork and into rock-filled scene unlike any other the mission has explored. A rocky outcrop in an area along the west wall the team named San Miguel shouted of the diversity before them.
The pipeline of images the rover sent home revealed a bounty of rocks distinguished by their texture, and rough, pitted exteriors, as well as rows of tiny rocks on the terrain that look like stone stripes, formations where the soil and gravel particles appear to have become organized somehow into narrow rows or corrugations parallel to the slope. All seemed to be hints that the rover was driving deeper into Mars’ geological history.
The robot drove past San Miguel and angled to the north/northeast to check out some intriguing textured outcrop nearby, along the edge of the north fork that the team christened Ojo del Muerto. But the team chose another textured rock target nearby and Opportunity wrapped the month at Jornada del Muerto.
The composition of these rocks weren’t quite like anything they had seen before and could be a new class of rocks discovered by the mission, but they weren’t quite all that strange either. The scientists began referring to them as San Miguel class.
“Mars continues to surprise us,” said Arvidson “We’re seeing stuff we’ve never seen before Perseverance Valley really is a brand new mission.”
The team quietly celebrated Opportunity’s 14th birthday on January 24th. The MER mission officially completed 14 years of surface operations on January 3rd, the anniversary of Spirit’s landing, but for the rover that has shattered every rover record on Mars, this 14th birthday was and remains an unparalleled achievement in planetary exploration...all the more remarkable considering the rovers were each only “warrantied” to last 90 sols.
Opportunity has been on this expedition for so long now that roving on Mars for some people has become “part of the daily routine,” as Wendy Calvin, of the University of Nevada Reno, a member of the MER Athena Science Team, put it. “You check your email, have a cup of coffee, go to Mars,” she said.
“We love that feeling of exploration,”Squyres reflected then.“But it’s important to not lose that sense of wonder, that sense of how fortunate we are to be able to do what we do.”
A series of wind gusts coming up from the floor of the crater whisked a substantial amount of dust from Opportunity’s arrays in January, leaving them almost sparkling. “Our energy has jumped way up,” reported MER Power Team Lead Jennifer Herman, of JPL.
Roving into February, Opportunity was empowered, as ready as ever to continue NASA’s first overland expedition of Mars. “We went from struggling through this winter to crazy beautiful power margins that are so fantastic,” said MER Mission Manager Scott Lever.
Despite a broken shoulder, the loss of her long-term, flash memory, and the capability of steering with her two front wheels, the robot soldier on through the month, getting her job as the team’s field geologist done. Steering with her rear wheels, Opportunity, with a lot of help from her drivers, navigated her way down, up, and along the slopes inside one of the most exciting and important geological sites of all her years on Mars.
“Every time we get a new vantage point, it’s just breathtaking,” said Barbara Cohen, of NASA Goddard Space Flight Center, a member of the MER Athena Science Team. “We hoped for more with Endeavour. The fact it’s delivering is just fantastic.”
After completing her investigation of Jornada del Muerto, which looked a lot like the so-called blue rocks that the rover examined in Marathon Valley in December 2015, Opportunity spent quality time on acquiring a combination of Navcam and color Pancam stereo panoramas, as well as targeted multi-spectral Pancam images. And on February 16th, the rover that loves to rove completed her 5000thMartian day of surface operations and set another astonishing record.
"We've reached lots of milestones, and this is one more," said Callas. “But more important than the numbers are the exploration and the scientific discoveries."
In honor of this Martian milestone, a group of the MER ops team hatched a plan for Oppy to do something neither she nor her twin Spirit had ever before done, take a full body, self-portrait. Rover Planners Ashley Stroupe and John Wright, and Visualization Producer and Engineering Camera Payload Uplink Lead Doug Ellison assumed the initiative of pitching the idea and calculating how the rover would use her Microscopic Imager (MI) to complete the task. “We deliberately kept it simple, so we could keep it fast, and within reasonable data volume,” said Stroupe.
Opportunity delivered, getting all but a small part of her right front wheels and solar array.The images, though expectedly a little blurry, turned out so good that the selfie crew and the rover were given time to fill in the missing frames for the official NASA-JPL black and white version, which the agency promptly released.
During the latter part of February, Opportunity continued to take extensive stereo color Pancam panoramas and Navcam panoramas at this stop before moving on.The rover’s last drive of the month took her back to the south. She stopped not far from where she began 2018, at the outer edge of a formation the team unofficially dubbed “the island,” because its presence likely caused the forks in the valley’s anastomosing or branching structure.
Opportunity eased into March taking targeted images of the streamlined island-like feature just christened Ysleta del Sur. As it turned out, the robot spent much of the month checking out a couple of outcrop targets at the “nose” or “upstream” end of the elongated geological feature. “We stopped to see if we could see any evidence of fluvial erosion,” MER Project Scientist Golombek said then. “What we see is this incredibly smoothed off surface that has strong evidence for aeolian abrasion. There are these little wind tails around rocks that are resistant.”
After shooting Pancams of a rock named Aguas Calientes, Opportunity zeroed in on the target and conducted an in-depth investigation using her MI, APXS, Pancam, and for the first time in 321 sols even twice deployed her Rock Abrasion Tool (RAT) to grind off a total 4 millimeters from the surface.
As with every stop on her journey through Perseverance, the robot used both her Pancam and Navcam to visually document the place and the valley’s morphology or structure. Eventually, all this visual data will be used to create a digital elevation model (DEM) of Perseverance that will give scientists an in-depth look at this unique valley formation that they can then visit and study again and again.
With spring beginning to take hold, the weather at Endeavour was as good as it gets this time of the Martian year. “It’s not too hot, not too cold, and the rover has plenty of power, upwards of 650 watt-hours, so it’s really an ideal time to be exploring,” said Nelson.
From the nose of Ysleta del Sur, Opportunity had to make a challenging heading change to get to her next destination, a long linear group of dark glassy rocks chock-full of holes at the southern border of the south fork. On the gravelly downward slopes of Perseverance, it proved to be a trial. “There are clear signs that she did not like what we asked of her,” said JPL Rover Planner Paolo Bellutta, who oversees the charting of the rover’s drives. “But she was there waiting for us to tell her what to do next.”
At the new site, San Juan Pueblo,Opportunity found herself in yet another fascinating geological world, rich with rocks distinguished by their pits or holes. “Vesicular rocks are characterized by these little cavities known as vesicles that are formed when you have a magma or lava that degasses and leaves holes,” Arvidson said. The scientists thought they might have been spit out and formed by a volcano. The robot field geologist spent the final sols of March shooting them with her stereo Pancam.
Meanwhile, on Earth,Opportunity shined for the 15th year in a row at the 49th annual Lunar & Planetary Science Conference (LPSC). From rocks that that hint of past water, the structure of the crater rim segments and their fault zones to the rare occurrence of the reactivation of certain faults and winds sand blasting the valley to an ancient lake that spilled over, the scientists told of enigmatic clues and considered all the working hypotheses and – left the doors open, as covered in The MER Update Special Report. “It’s a work in progress,” as Squyres concluded in his opening presentation.
Perhaps the true indication of this mission’s enduring significance in planetary exploration is the fact that of the six scientists who presented on Opportunity’s findings at the conference session on Depositional and Environmental History, two were young PhD candidates, both interestingly enough from Washington University St. Louis, the home turf of Arvidson: Michael Bouchard searched for clues to the origin of Perseverance by comparing the composition of rocks there to other rock suites observed along the rim of Endeavor Crater; Madison Hughes who used orbital imaging of Endeavour and a landscape evolution model (MARSSIM) to determine the degradational history of this 22-kilometer (13.7-mile) diameter crater, or in other words, find out how it has “aged” over the last few billion years.
When April dawned at Endeavour, Opportunity was still at San Juan Pueblo checking out the strange, maybe-vesicular, definitely pitted rocks. With a total of45.13 kilometers (28.04 miles) on her odometer, she was boasting a solar array dust factor of 0.836 and producing about 680 watt-hours of energy under hazy skies. Tau was estimated to be 0.653. Who would’ve thunk the rover could be so energetic after more than 14 years of roving around the Red Planet?
Opportunity spent the month exploring more of the central valley area to the south and west of Ysleta del Sur, conducting in-depth investigations using the mission’s standard MI and APXS protocol on one of the unusual,shiny new objects – the charcoal gray ‘vesicular’ or pitted rocks. Although the scientists thought these specimens could be volcanic basalts, the rover’s research seemed to show they weren’t, leaving team members stumped.
“It’s definitely not basalt,” said Golombek. “It is higher in silica and it has an unusual composition that is not like most of the things that we’ve seen. Some of the vesicles look like they’re filled with other material, different, maybe after-growth minerals or something. It’s a very interesting rock.”
“The unique cut into the wall of Endeavour is exposing rocks we haven’t seen before,” said MER Deputy Project Scientist Abby Fraeman, of JPL-Caltech. “That has been really interesting and not expected and really cool. The chemistry and the textures are different than anything we have seen in the rim of Endeavour or in the Burns Formation.”
One possibility is that these dark, pitted rocks may be impact melt that date to the Big Thunderous Thud that created Endeavour, perhaps pseudotachylites, a type of fault zone melt generated from intense throw and frictional heat within fractures, as Crumpler theorized at LPSC. “The vesicular rocks are right between two fractures” that “are parallel to all the other indications of fractures in the valley,” he noted. This finding would support his hypothesis that Perseverance is strongly fault controlled, as well as his suggestion that these rocks may be impact melt.
MER Athena Science Team member Jim Rice, Senior Scientist at the Planetary Science Institute put forth another hypothesis in a MER meeting, that weathering sometimes forms this unique kind of texture on rocks. The research on Earth continues.
From San Juan Pueblo, Opportunity roved upslope, heading toward some tabular rocks, so named because of their layers or plates, or, in geology jargon, laminae. Again, the Martian terrain made for some tricky, slope-slipping driving for the rover because of a light layer of sand on the rocky terrain she was trying to traverse.
As the rover struggled, she wound up possibly breaking up a pitted rock and churning up the patch of soil it was sitting on. Inside the mess, was “beautiful, colorful debris,” said Arvidson. It could be, he suggested, a “goldmine.”
Opportunity imaged the “colorful debris, using the Pancam system’s 13-filter, multispectral capabilities, which enables the scientists to characterize and distinguish between different mineralogical units of targets. “A lot of the color differences in the scene are not associated with definable spectral characteristics that I could assign any kind of mineral ID to,” said MER Athena Science Team member Bill Farrand, Senior Research Scientist at the Space Science Institute. “So it is colorful, but a little frustrating from a Pancam perspective in terms of interpretations.”
The scene is relatively flat, where the robot wouldn’t have to risk doing IDD work on irregular rock surfaces, but an in-depth investigation would have to wait.The tabular rocks, of interest to the science team for weeks, were next up. As Opportunity pressed on upslope, she drove right by the tabular rocks on what turned out to be a necessary circuitous route. And, at month’s end, the robot wound up perched over another pitted rock, named Allende. Once her work was done there, the “next stop will be the tabular rocks,” said Golombek.
As the Martian spring moved in, the robot’s external wall temperature rose to as high as -8 Celsius [17.6 Fahrenheit] during the day, and was only dropping to around -80 Celsius [-112 Fahrenheit] at night, according to Callas. With almost sparkling solar arrays, whisked clean during the last several months by winds coming up from the interior of the valley, the rover’s energy was robust, nearly three-quarters of her full power production capability on landing.
Perseverance Valley was looking to be an increasingly complex story. “It could be a multitude of processes that carved this formation,” Fraeman said. “But we are determined to get to the bottom of this thing and explore all the possibilities.”
Early in May, Opportunity finished up her investigation of Allende and headed for some tabular rocks in the south fork. The robot ended up hunkering down over La Joya for an in-depth investigation. Despite the slip-sliding driving, the rover continued showing her MER mettle. “The vehicle is well behaved and is currently moving on a slope of about 24 degrees,” said Bellutta, at month’s end. “Lately, we have been driving mostly cross-slope with the vehicle tilted to the left and pointed due south. The rover is very stable. She seems to be glued to the road like a Porsche.”
Opportunity took a few breaks in the rock action to look skyward. In the process, she acquired images of the Martian moon Deimos, and also managed to make a little MER ‘movie’ of Phobos’ transit Mars. “It was nice to get the Deimos one, especially. They are more rare due to the orbit geometry,” said Mark Lemmon, then Associate Professor at Texas A&M, now Senior Researcher at the Space Science Institute.
The rover also conducted relay tests with the Trace Gas Orbiter (TGO), which was in its commissioning phase. Part of the ExoMars program led by ESA and the Russian Roscosmos State Corporation, TGO is a much-needed and welcomed addition to the Mars communications constellation.
On May 22nd, the spring equinox in the southern hemisphere of the Red Planet came and went. Although the sky was a bit dustier than in the last couple of months,the rover basked in the warmth of her eighth Martian spring, continuing to produce more than two-thirds her capability as determined on landing when she was “new” and had sparkling arrays.
“What’s interesting is these outcrops change in texture and in color as we go from north to south,” Arvidson noted. “We’re trying to look at all the different kinds of rocks in this complicated zone that might be fault-controlled, investigating what’s causing patterns we see in terms of the material properties, and working to understand the nature of each one,” he added.
As the fourth week of May began, Opportunity focused on completing her investigation of La Joya, with an offset target on a dark part of the outcrop. “It’s either a rock embedded in the outcrop or just a different color, we’re not sure,” said Arvidson. But nothing unusually strange or particularly exotic emerged from the rover’s findings here or from the tan-colored tabular rocks. That is to say, both types look pretty much like rocks the MER scientists has previously encountered. “The tabular rocks are not particularly high in silica or other stuff, just kind of within the family of other rocks we’ve been seeing on the rim,” he said.
Even so, Opportunity took the time to collect more images to add to a tabular rock panorama, as well as some additional site imaging. From LaJoya, the rover maneuvered her way to another chosen tabular outcrop called Inde where she spent the rest of the month, conducting another in-depth investigation.
As May began fading to June, the rover was busy and “doing wonderfully well with good energy and moderate internal temperatures,” said Nelson,still producing upwards of 650 watt-hours of power with a dust factor hovering around 0.774.High on the team’s ‘to-do’ list was a return to the spot near the pitted rock Allende, where the rover churned up the soil and possibly broke or at least moved another pitted rock as she had struggled to climb up the nearly 25-degree slope in April. But an ominous threat loomed on the horizon.
A local dust event that kicked up in the northern hemisphere and followed the Acidalia storm track had crossed the Martian equator and was growing into a regional storm not too far away from Endeavour. On June 1st, Bruce Cantor, of Malin Space Science Systems, the weatherman who posts Mars Weather Reports each week based on data from Mars Color Imager (MARCI) on MRO, alerted the MER team.
Within the week, the storm grew as it crossed the equator and then, at Endeavour, not far from Opportunity, it stalled. Over the next several days, the winds lifted huge amounts of dust high into the atmosphere, blotted out the sky, and presumably thrashed the rover with the powdery rusty-red stuff of Mars. “When we first heard about this thing, it covered 13 million square kilometers, then grew to 41 million square kilometers (15.8 million square miles) and it’s still growing,” Nelson said in mid-June.
The solar-powered rover’s energy dropped dramatically. The MER ops team members didn’t really know just how dramatic the drop was until Sunday, June 10th, when they received a downlink from Opportunity. The downlink alone was a positive sign, but the vital statistics were nearly incomprehensible.
The measurement of the opacity or dust in the Martian atmosphere, estimated at 10.8, was greater than the rover has ever recorded, doubling the previous MER record of 5 to 5.5, during the planet-encircling dust event Opportunity survived in 2007, according to Lemmon. In fact, the jaw-dropping measurement overtook the all-time record Tau of 9 held by the Viking landers during a PEDE back in the late 1970s.
Worse, Opportunity was producing just 22 watt-hours of power, nearly 100 degrees less than what was considered necessary for survival for a MER class rover. Callas declared a spacecraft emergency. And at some point soon after sending that downlink, the rover shut down and hunkered down.
“This is the worst storm Opportunity has ever seen, and we're hoping for the best,” Squyres told The MER Update Special Report. It was really bad. “The dust here is thicker than anything I have ever encountered, going back to Viking missions,” added Arvidson, who served as Science Team Leader for the imaging system on NASA's Viking Landers from 1977 to 1982. “It’s dark, like the end of twilight dark.”
NASA held a media teleconference June 13th. “We’re very concerned,” said Callas. The storm was “just days away from meeting the classification of a planet-encircling dust event (PEDE),” announced Rich Zurek, the Chief Scientist of JPL’s Mars Directorate and of MRO.
The team started reaching out within days, sweeping the frequencies and commanding a single beep three days a week just to see if they could make contact with the rover. “But we knew this would be a long haul and that we would be out of contact for months,” said Nelson. Backstage at Mission Control at JPL, the mood was “optimistic but somber” as Bellutta described it.
This isn't Opportunity's first dusty rodeo. But this time, the monster storm “seemed to be a direct hit from the regional storm that kicked off the activity,” said Lemmon.
Scientists have been tracking these rare, planet encircling dust events (PEDEs) on Mars for more than a century, beginning with telescopes on Earth, and in recent decades, with instruments on spacecraft orbiting Mars. In its fury, this global storm, which would be declared a PEDE on June 20th, offered “an unprecedented opportunity to learn more about Mars, and the many challenges that it presents for exploration,” as Jim Watzin, Director of the Mars Exploration Program at NASA Headquarters, defined it during the teleconference.
The space agency enlisted every one of its assets at Mars – the Odyssey, MRO, and Maven orbiters, and, on the surface, Curiosity – to observe and study this massive storm from many different perspectives with cameras and other science instruments. “Dust storms are the largest weather event we see on Mars. That’s why we get excited about them,” explained MER Athena Science Team member Michael Doyle Smith, of NASA Goddard Space Flight Center, who is among the atmospheric scientists studying this PEDE.
While these global dust events are usually referred to as one storm, they are actually comprised of multiple “dust-lifting centers” or dust devil-like funnel clouds that pop up or grow and intensify, as the storm moves along. So, while a storm can engulf an area in its direct path, another area may have more action on the ground, be closer to the ‘ground zero’ of a lifting center so to speak, and render a more deleterious impact.
Opportunity wasn’t near any lifting centers in 2007, but was perilously close to one in this storm. This proximity, noted Mars atmospheric scientist Michael Wolff, Senior Research Scientist at Space Science Institute (SSI), might also explain the “extraordinary amount” of atmospheric dust the rover last recorded.”
“This storm came on so fast,” said Herman. “It was so early, and so big. That kind of scared everyone.”
On June 28th, the team got a letter from NASA HQ informing that the MER mission was granted its proposed one-year extension for 2019.
Through July, the PEDE continued lifting dust from the Martian terrain high into the atmosphere, perhaps altitudes “in excess of 60 kilometers,” Cantor estimated. That’s more than 37 miles or seven times higher than the 30,000-foot altitude at which most large passenger jets fly. Then, it blanketed the planet with a dust cloud.
Planet encircling dust events are highly dynamic and wildly unpredictable. The atmosphere above one area, for example, may clear for a bit and then get dusty again depending on the intensity of dust-lifting activity nearby and which way and how strongly the wind is gusting. By late July however, Cantor estimated that the dust opacity at Endeavour had dropped substantially, to approximately 3.6 with a margin of error of 1, meaning the haze could be as low as 2.6 or as high as 4.6, “a huge uncertainty,” he admitted. Along with that though, he saw what he believed were the first signs the tempest had peaked.
“We’re starting to see surface features in more places; the middle atmosphere is starting to cool down a bit; and the dust lifting centers seem to be petering out,” as Zurek summed it up.
Still, it would still be weeks before the sky over Endeavour cleared and the rover could take in enough sunlight to charge her batteries and phone home. But down was better than up in this case and toward the end of the month.
Despite all the uncertainty, there were good reasons for optimism. The surface was still warm from the planetary dust blanket insulation. It was spring and the summer solstice wasn’t arriving until mid-October, so Opportunity wouldn’t have to tap into her precious battery power to keep warm any time soon.
Moreover, Mars had just passed through perihelion, the closest the Red Planet will get to the Sun in its eccentric orbit until 2020, and new thermal modeling indicated that the rover should stay above her minimum allowable operating temperatures. That wasn’t all: the rover’s batteries were estimated to have 85% capacity left, even after 5000 charges and discharges, informed Callas.
From a comparison with the 2001 dust storm, which Cantor assessed was the one most like this one in recent, orbit-observed history, he predicted that the Tau at Endeavour should drop farther down to 2 or so sometime in September.
The ops team kept to routine, building strategic communication windows for the orbiters, even though they won’t be used until Oppy phones home. “When we do resume we’ll be ready to jump in,” said Lever. Other than that, Bellutta said: “All is quiet,”
Over the last 14-and-a-half years, Opportunity and the MER ops team have made exploring Mars almost easy, a matter of course despite the extraordinary challenges. But it isn’t easy. Not at all. Not ever. “No one knows for sure what’s going to happen,” said Stroupe. “But the team is working hard and putting everything into trying to make sure we are 100% ready to go to help recover the spacecraft.”
In August, the PEDE entered its secondary decay phase and all the dust that was lofted high into the atmosphere began settling out and drifting back onto the Martian surface. With skies clearing and sunlight streaming through the tears and thinned out spots in in the planet’s dust-blanket, the skies brightened over Endeavour.
Some team members were hopeful Opportunity would attempt to call home, but most thought it was just too early. The ops team at JPL focused their attentions on reviewing, tweaking, analyzing the various possibilities and contingencies for any and all potential issues, contributing their efforts to a recovery strategy.
Herman had just completed an historical review of the mission’s data through the different Martian seasons, as well as conducted some new simulations. This much was clear, she said: “In order for us to hear from Opportunity’s solar arrays needed to be fairly clean.” In all likelihood, however, with history as the guide, the rover still was taking on dust.
“When we get just past the summer solstice, on October 16th, we should start to see the winds cleaning off the solar arrays again,” said Herman. The windy cycle was slated to begin in mid-November and blow through at least January 26th, 2019. “Every single Mars year, we have seen dust cleanings in this timeframe,” she noted.
At the management level, Callas pulled together a plan, cleared it as requested through a peer review at JPL in mid-August, and then developed it to meet NASA’s approval.On August 30th, the space agency announced its decision to adopt a two-step plan to try and recover Opportunity, in a press release quietly posted online.
Once the Tau dipped below 1.5, the ops team with the help of DSN operators would begin a 45-day period of actively attempting to communicate with the rover by sending it commands. If the team was unable to pick up any signal from the rover, a small core group of MER team members would stay on for “several months” more to continue listening “passively,” continue ‘keeping an ear out’ for the ‘bot by scouring all the radio frequencies emanating from Mars.
Since there was no data coming from the rover, the only viable estimation of Tau had to come from orbit, specifically Cantor, using Mars Color Imager (MARCI) data and modeling software developed by Mike Wolff. The ops team was already conducting both of these strategies. Now it would be allowed to increase their efforts, for a limited time.
“In a situation like this you hope for the best but plan for all eventualities,” Callas stated in the release. “We are pulling for our tenacious rover to pull her feet from the fire one more time. And if she does, we will be there to hear her.”
The press release stirred immediate reaction from the mission’s followers on social media. With a 45-day limit being put on the first phase, and several months for the second, some people ‘read’ that as NASA giving up on Opportunity.
Zurek subsequently challenged that notion. “We’re not going to give up as long as there are reasonable things to try,” he told The MER Update. And, in coming days, NASA would update the plan and assure the rover’s followers that the agency did have Opportunity’s back.
As the dust continued settling out, the sky over Endeavour brightened noticeably in September. The storm would soon be officially declared over. Although the Tau was on the hazier side of the Martian winter spread, it had dipped to 1.5 for three consecutive days.
So, on September 11th, the MER mission ops team initiated the first phase of the NASA-approved plan to reestablish contact.The engineers increased attempts to actively search for the rover’s signal with the DSN antennas from three times a week to multiple times each day, hoping to latch onto the rover’s signal and electronically nudge the ‘bot to respond. The start date, as per the press release, put the end of the 45-day period of active commanding and listening in late October.
The team also broadened the range of times and frequencies on which they looked for Opportunity’s signal among all the signals from Mars recorded by the most sensitive radio receivers at the network’s stations in California, Australia, and Spain.
“The real concern is the dust,” said Staab. Actually, the original MER team talked about the dust a lot and the generally held belief back then was that the dust would be the most likely cause of demise for both Spirit and Opportunity.
At the same time, the MER mission’s history does clearly, consistently show that good gusts of dust-clearing winds typically blow the rover’s way during the dust storm season, and should come through Perseverance beginning in mid-November 2018 through the end of January 2019. Once, they even blew into March and the very end, arguably, of the dust season. Plans were put into the works in September to try and look at all that darn Martian dust and monitor recent surface changes with the various instruments onboard MRO, according to Arvidson.
Meanwhile, the 45-day endpoint for active commanding was looming. “NASA continues to keep saying to me that they fully support the recovery of this rover,” Callas told The MER Update in September. And they want us to do all we can to try to recover Opportunity.”
Indeed, Thomas Zurbuchen, NASA's Associate Administrator for the Science Mission Directorate, who makes critical decisions with regard to this mission, along with Mars of course, showed support on Twitter in early September. “Rest assured we are not giving up,” he wrote. “We are listening and working to recover Oppy. The mission is funded through end of FY19.”
Nevertheless, it was still a race against time with so many odds against them. Anxiety darkened the team’s characteristic optimism as team engineers especially felt the pressure bearing down. “We’re doing all the right things,” assured Squyres.
The moment of the month arrived when Alfred McEwen, Principal Investigator of HiRISE camera onboard MRO and Director of the Planetary Image Research Laboratory at the University of Arizona, sent the team the HiRISE image of Opportunity in Perseverance Valley. In the words everyone on the team: it was really nice to see Opportunity again.
Although hope was floating all around October, there was still no signal, no phone home from Opportunity. It was no surprise for some, but discouraging for other members of the MER team.
The ops team, which continued rehearsing and reviewing preparations for recovering Opportunity, placed themselves at DUSTCON 1. It was an unofficial, self-imposed description of their level of readiness. Inspired by the U.S. military’s DEFCON system of five graduated levels of defense readiness, they adapted it and deployed it “for fun and inspiration,” said Herman.
It was clear however that the team was missing Opportunity, a lot. “It’s pretty much a bummer,” said Golombek. “The rover is like part of our family.”
By now, there seemed little doubt that Opportunity was one dusty rover. “My feeling remains that it is likely a lot of dust was stirred up and fell locally,” said Lemmon. “Opportunity [was] at the epicenter of the storm.”
On October 29th, after reviewing the team’s efforts, NASA Headquarters officials published good new son the MER website, which offered clarity on the plan moving forward. The team, the agency announced, could continue both the active commanding and passive listening strategies to find Opportunity’s signal “for the foreseeable future.”
Other than getting a downlink from Opportunity, it was about the best of Halloween, “treats” they could hope for. “Active listening through January is a boost to our chances of hearing from the rover if the arrays are very dusty now,” said Squyres.
It also alleviated a huge amount of pressure, allowing the ops engineers to breathe again, if only for a few minutes. “It has,” said Staab, “really invigorated us.”
While the decay phase of the PEDE continued into the first sols of November, by the end of the first week of the month, the Tau over Opportunity’s site had dropped to 0.8, Cantor reported, and dust activity across much of Mars was “relatively uneventful.” It was good news the team embraced.
The MER team and DSN operators pressed on with the search throughout the month, even as InSight closed in on the Red Planet and NASA and JPL focused on getting that lander down on the surface safely. They expanded both steps in the plan, increasing the sweep-and-beeps, and broadening passive listening to “virtually every DSN track from Mars,” as Golombek put it, hoping to hear something, anything from Opportunity.
A host of false alarms lit the Twittersphere, but the signals all turned out to be from other spacecraft. “MRO is our primary culprit,” said Staab, because it propagates on a radio wave close to Opportunity’s.
As tenacious and undaunted as their robot, the MER team had not lost hope, not yet. “We have done some new thermal simulations and it looks like we’re not in imminent danger of having heaters turn on,” Nelson informed. From the most recent HiRISE image of the Opportunity site, there was no discernable change at the site, and no obvious indication that dust-cleaning winds have kicked up since the windy season began.
Once they do make contact with Opportunity, if they are able to do so, the MER engineers will have to address a mission clock fault, a low-power fault, and an up-loss timer fault. They are well prepared for that and just about anything else imaginable, except a broken part.
The ops team continued routine planning as they have since Opportunity checked into hibernation. “We’re still building the plans so all the tools still flow and the team stays in the routine of operations,” said Herman.
The MER science team kept “forging ahead” too, as Fraeman described it.
Arvidson started the draft for MER’s 12th mission extension, asking for volunteers to contribute ideas and geological desires. This extension would keep Opportunity roving for three more years, take the mission through Perseverance Valley, and into Endeavour, if the team succeeds in recovering its robot field geologist.
On November 25th, McEwen sent the latest HiRISE image of Opportunity and Perseverance Valley to the team. It didn’t seem there had been much change in the scene at all. “If the windy season has begun, it doesn’t seem to have impacted Perseverance Valley or Opportunity yet,” said Arvidson.
Even though “November was essentially a repeat of October,” as Staab said,the beginning of dust season in mid-November lifted spirits and hope still floated through the MER halls. “It’s still summer in the southern hemisphere of Mars and it’s not that cold,” Herman said. “We’ve only been in dust-cleaning season for 12 days at best.”
Meanwhile, Cantor was keeping an eye out for any new, potentially threatening dust storms that may blow Opportunity’s way. “Mars is pretty quiet these days,” he said. “The big storms don’t pickup again until the latter half of December into January 2019. Now is a good time for a dust devil cleaning event,” he said
“Hope still springs eternal here,” said Nelson. “But it’s been a long wait and anticipation does run high at this point.”
Not so happily, December turned out to be a repeat of November. No threatening dust storms picked up, but a good regional guster that sends some dust-cleaning winds Opportunity’s way is what the MER mission needs now more than ever.
As usual, the end of the year holidays meant downtime for most team members and ‘quiet’ turned out to be the operative word of the month.
“It’s been extraordinarily challenging and tough for this rover. This was the worst dust storm in 40 years,” Squyres said. “But as I’ve said many times over the years, you could lose a lot of money betting against Opportunity. We’re going to keep trying. That’s where we are right now.”
In the meantime, why not send a postcard to Opportunity?