A.J.S. RaylAug 01, 2017

Mars Exploration Rovers Update: Opportunity Enters Perseverance Valley, Settles in for Solar Conjunction

Sols 4776-4805

After struggling to get her left front wheel unstuck in June, Opportunity quickly adapted to a new driving strategy and unabashedly cruised into Perseverance Valley in July, making it look easy as she drove onto a small knoll to wait out solar conjunction. Then, as the routine celestial event pulled Mars behind the Sun and the veteran explorer got to work on autopilot, something unexpected happened, leaving the Mars Exploration Rovers (MER) mission with an unwanted mystery to solve as August came over the horizon.

For years, even before Opportunity pulled up to the western rim of Endeavor Crater and Cape York in August 2011, the MER scientists had their eyes on Perseverance, a shallow valley carved into the rim farther south at Cape Byron. It’s as unique a geologic site as they’ve seen on the entire mission, and it hints of the past water and habitable environments they had come to Meridiani Planum to find.

In July, the robot field geologist put the point on the exclamation mark on a quest that has been 13-and-a-half years in the making. At long last, Opportunity was inside the Perseverance Valley. She had arrived!

Tantalizing signs inside Perseverance
Tantalizing signs inside Perseverance Opportunity took this image with her Panoramic Camera (Pancam) not long after driving into Perseverance Valley. In the middle of the frame you can see a deep gouge or channel that resembles the grooves the rover found atop Perseverance and seems to hint of past water. The Pancam team at Arizona State University (ASU) processed this image in false color, a technique scientists use to better discern the various geological elements in the scene.Image: NASA / JPL-Caltech / Cornell / ASU

“Perseverance has been calling us for years,” said MER Principal Investigator Steve Squyres, of Cornell University. “Exploring the valley is the next big science phase of the mission. This is just tremendously exciting.”

About 20 meters (21.87 yards) wide, the valley stretches downslope from the rim some 180 meters (196.85-yards) to the floor of Endeavor Crater, which dates back the Noachian Period 3 to 4 billions of years ago when Mars was warmer and wetter and, scientists generally believe, more like Earth. Since Opportunity is the only robot to have ever explored the rocky remnants of this ancient Martian time, Perseverance is a big exploratory deal.

Although Opportunity uncovered evidence for water and clays and past habitable environments at Cape York on Matijevic Hill, Perseverance could turn out to be the most telling site the rover and her Earth-bound colleagues will visit. “The work we do here will be the first ground-based exploration of a preserved valley system on Mars,” said MER Deputy Principal Investigator Ray Arvidson, of Washington University St. Louis.

The MER scientists will be testing several hypotheses to determine how this valley was formed. The leading theories, which propose flowing water or a debris flow or fracturing ice or even, perhaps, wind, are all in play right now. Opportunity will drive through the valley imaging everything around her searching for geomorphic and sedimentological evidence that will enable the MER scientists to figure it out. Since the mission’s eighth Martian winter about to blow in not long after the solar conjunction ends in early August, the plan called for the solar-powered rover to negotiate her way downslope in 20-meter “hops,” driving from one north-facing slope, or lily pad as the team members call this winter-friendly slopes, to another in order to take in as much of the winter Sun as possible.

Solar conjunction
Solar conjunction About every 26 months, when Mars and Earth are on opposite sides of the Sun, communication between the two planets is disrupted. During the days surrounding such an alignment, called a solar conjunction, the Sun can disrupt radio transmissions between the two planets.Image: NASA/JPL

First they had to contend with solar conjunction. Once inside the valley, Opportunity drove onto a little knoll, angled at about 10 degrees with her solar arrays facing to the north where she can soak up the warmth of the late autumn Sun. “So far it seems like the rover is responding well using the rear wheels as steering wheels and tank turns to change direction and maneuver around things,” said Rover Planner Paolo Bellutta, following the drives into the valley and onto the knoll. “The telemetry and imaging that we received from the last few drives indicate the vehicle is working fine.”

From the scientists’ perspective, the first glimpses of the geomorphology inside the valley are plenty intriguing. One image that Opportunity sent home clearly showed more linear grooves or channels that point downhill. “The images from where we are for conjunction are as tantalizing as the images of the channels on top of Perseverance,” said Arvidson.

But the MER team had to hit the pause button on excitement for a couple of weeks. “It’s like: ‘Darn, we’ve just arrived and now we have to wait,’” said MER Project Manager John Callas, of the Jet Propulsion Laboratory (JPL), home to all the American Mars rovers.

Time flies when you’re having fun, as the saying goes. And between the rover adjusting to new driving techniques and the team’s urgent desire to get the rover parked and settled in before solar conjunction, Opportunity’s grand entrance into Perseverance turned out to be a rather quiet achievement, greeted with more sighs of relief than jumping cheers. No one however complained.

“We knew that this knoll would give us decent power and that we’ll have decent power at the end of solar conjunction to allow Opportunity to drive on to the next northerly slope or ‘lily pad,’” said JPL’s Chief of MER Engineering Bill Nelson. 

Solar conjunction comes around about every 26 months when the orbits of Mars and Earth put the two planets on opposite sides of the Sun, and so this is the MER mission’s seventh go-round at this cosmic rodeo. Since plasma emanating from the Sun can and does disrupt signals between the two planets, NASA and JPL institute a two-week communication blackout period, and a complete moratorium on sending any commands to Opportunity.

“Out of caution, we don’t send any commands to the rover during this period,” said Chad Edwards, the Manager of the Mars Relay Network Office at JPL. “We don't want to take a chance that one of our spacecraft would act on a corrupted command.”

Parting view atop Perseverance
Parting view atop Perseverance 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 false color.Image: NASA / JPL-Caltech / Cornell / ASU

While Opportunity is out of “sight” on the other side of the Sun, Edwards and his crew in the relay office do however enable the MER ops team to monitor the goings-on and the general status of the rover as best they can. “Every day Mars Odyssey and the Mars Reconnaissance Orbiter (MRO) continue to fly over the landing site, so roughly one or two times a day we will exercise the relay link to one of those orbiters.”

None of the rover data stored on MRO will be downlinked to Earth until the solar conjunction moratorium is over. However, the relay team does make “a best effort” at sending some of the data from Odyssey down to Earth during the communications blackout. “We try on a day-by-day basis to send telemetry through Odyssey with the understanding that because of the plasma effect a lot of that downlink to Earth will be corrupted,” said Edwards. “Nonetheless, what does come through gives us some visibility into the status of Opportunity.”

That’s how the MER team found out about the unexpected happening. Just a day after the blackout began, on July 23rd, the ops team engineers received data that informed them that Opportunity had stopped working on her assignments and checked into automode. “The rover had a warm re-boot and is now in what we call automode, safe mode to everyone else,” confirmed Nelson. “We believe the re-set of the rover's computer happened on Friday, July 21st during the morning X-band communication session and that stopped the stored master sequence of commands.”

The sudden re-boot could have been caused by a coronal mass ejection (CME) or solar flare from the Sun. Such events, said Edwards “can cause what we call single event upsets in our electronics and lead to a software anomaly or computer anomaly and shut the computer down or put it into a safe mode.” But, he added later: “I’m not aware of a specific CME event correlating with this MER reset.”

Another possibility is that Opportunity’s sudden re-boot could be the result of some glitch or failure in some part of the rover’s hardware or software. Or it could have been caused by an error somewhere in the sequencing of the rover’s commands. Since they cannot command the rover, the MER ops engineers won’t be able to investigate until after the moratorium is lifted in early August.

“We’re not stressing too badly, although everyone worries about why this happened,” said Nelson.

Opportunity is designed to autonomously protect herself when things go awry and in automode she is a safe and stable state. “The moratorium ends in the mid-afternoon on Mars, August 1st on Earth,” said Nelson. “We have a contingency uplink track the following day on which we will recover the rover. But for the time being, he said: “We’re just going to have to ride it out.”

“This is another reminder that this rover is old,” said Callas. “It’s not like we’re in our golden years and taking it easy, watching the Sun set over the veranda, and sipping our tea. We’re now poised at one of the most scientifically interesting objectives of the mission after thirteen and a half years and Opportunity is still out there fighting it out with the unknowns on Mars to make discoveries and it hasn’t let up. But the rover is not immortal. We do have to be mindful of that every day.”

Optimism, though measured for some, continues to reign on MER. “It’s okay,” said Arvidson reassuringly. “When we wake up, we just need to go in and get the high gain antenna (HGA) going again and get the vehicle out of auto mode.”

Over the edge and into the valley
Over the edge and into the valley Opportunity took this image with her rear Hazard Camera (Hazcam) on July 6, 2017, as she drove of the edge of Endeavour Crater’s rim and into Perseverance Valley. The robot field geologist spent the month of August venturing deeper into the valley. Stuart Atkinson processed this view from the raw image the rover sent home.Image: NASA / JPL-Caltech / Cornell / ASU / S. Atkinson

The latest news — updated Aug. 4, 2017:  The MER ops engineers recovered Opportunity as planned on August 1, 2017 and recalibrated the gimbal angles on her HGA, which the team uses to uplink commands. The following day, with the rover’s HGA once again pointing appropriately to Earth, the team sent commands for the rover to check out the atmospheric opacity or haziness of the sky, take some images with her Panoramic Camera (Pancam), Navigation Camera (Navcam), and Hazard Cameras (Hazcams), as well as a still frame cloud ‘movie.'

“As hoped for, those commands executed flawlessly,” reported Nelson. “According to the data we’ve gotten so far, everything looks nominal.”

Since Opportunity works in RAM mode these days, and because RAM is volatile memory, which means when the rover shuts down for the night the data of the day is not saved, all the forensics that might offer clues as to why the rover suddenly re-booted are long gone. Therefore, the MER team isn’t really expecting to be able to pinpoint the exact cause of the sudden re-boot, though they are investigating the issue.

Whatever happened may forever remain a mystery but the MER mission is moving on. Opportunity is back at work and currently wrapping up the science investigations just inside the entrance to Perseverance Valley. “We decided that we have started the winter campaign at the conjunction location,” said Arvidson.

Anxious to get going, the team is planning on having Opportunity drive another 20 meters downslope as soon as this weekend, making "the first of what will be many stops,” Arvidson said. The plan, as previously reported, is for the robot field geologist to drive through the valley all the way to the floor of Endurance, stopping to rest every 20 meters or so on a north-facing slope to take in as much sunlight as possible for power production. At each stop or waystation, the rover will acquire a 360-degree Navcam, a high fidelity stereo panorama, targeted Pancam color and stereo images. She also willl examine targets up close “as they present themselves,” he said, using her Alpha Particle X-ray Spectrometer (APXS) to analyze chemical composition, and the Microscopic Imager (MI) to take extreme close-up pictures.

Post-Conjunction Views Inside Perseverance
Post-Conjunction Views Inside Perseverance After solar conjunction brought Mars out from behind the Sun and the MER ops team commanded Opportunity out of automode, the rover took these two images (above and below) with her Pancam . Stuart Atkinson, processed them from the raw images that the rover sent home.Image: NASA / JPL-Caltech / Cornell / ASU / S. Atkinson
View of Perseverance Valley post-conjunction

Deep Dive into July

When June turned to July at Endeavour Crater, Opportunity was stationed along the northern side atop Perseverance Valley and in the midst of finishing up an imaging survey of the surroundings with her Panoramic Camera (Pancam). In addition to focusing on some linear cuts or troughs in the terrain, perhaps channels that hint of past water, the robot was also taking various images of the area to be processed with the dozens of other images that Opportunity took in June for what the team humorously dubbed the Sprained Ankle Panorama.

That panorama-to-come is named, of course, in remembrance of the anxiety-fueling wheel event that brought gloom to June when the rover’s left front steering wheel stuck turned 33 degrees outward during a turn and then glory when the ‘bot and her human colleagues managed to straighten it, the event that will forever define how this month will be remembered, as well as how Opportunity would rove on.

Once her left front steering wheel was back on the straight and narrow, the robot field geologist took off under new drive restrictions: using only her rear wheels to steer and tank turns to change direction and maneuver around things. From the first drives to the north atop Perseverance, Opportunity handled it with aplomb. No big deal.

Eagle to Victoria to Tribulation to Perseverance
Eagle to Victoria to Tribulation to Perseverance These images show the routes that Opportunity took from her landing in Eagle Crater to Endeavour Crater, and then along the western rim of Endeavour Crater from Cape Tribulation to the top of Perseverance Valley. After emerging from solar conjunction in early August 2017, the rover drove deeper into the Perseverance Valley. The High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter (MRO) took the base images for these graphics. Larry Crumpler, a member of the MER science team, provided the annotations.Image: NASA / JPL-Caltech / UA / L. Crumpler / NMMNH

Although dust from the summer storms still permeated the sky and the robot was so dusty she was only able to utilize a little more than half the sunlight hitting her solar arrays, Opportunity was still producing upwards of 325 watt-hours of power as July took hold, enough to rove on and take images. But with solar conjunction about to occur and winter soon to blow in after that, there was some concern and a lot of talk among the MER team members about just where the rover would rove to.

There had been “quite a bit of commotion” about the left front steering wheel getting stuck, said MER Project Scientist Matt Golombek, of JPL. “We had quite a bit of discussion about where to spend solar conjunction, and then where to spend the winter and those discussions included lots of options that were all bandied about,” he said.

For Opportunity, now with two right front steering wheels that were not steerable, to navigate her way down the slope of the valley and move from one north-facing slope to another to ensure that she could work throughout the season, well – it raised questions. But it never became an arm-twister. “It didn’t seem to make much sense to stay up on the plains,” Golombek said. “We figured that at a minimum, if the valley has any topography, because it goes east-west, the southern edge would have north-facing slopes where the rover could park and position her arrays to the Sun in the north.”

At the end of the Martian day, the MER team concluded that they all wanted to go into the valley. The scientists wanted to get the science, of course. The rover planners and engineers were up for the challenge, and, from all appearances, so was Opportunity. Past that, said Golombek: “This valley is the highest science proposed for the extended mission and we don’t want to not do it.”

Decision made, on Sol 4779 (July 3, 2017), the robot wrapped her imaging assignments and her investigation of the troughs or channels atop Perseverance and headed toward the entrance of the valley, which cuts into the Cape Byron segment of the 22-kilometer (13.67-mile) diameter Endeavour Crater. The rover put 31 meters (almost 101.70 feet) to the northeast, behind her stopping just a short distance from the edge of the crater rim.

Bellutta, who created innovative software to chart the rover’s routes, had picked out a couple of potential destinations. Both were north-facing knolls on the southern wall of the valley just inside the entrance that should enable the rover to bask in as much of the autumn Sun as possible during solar conjunction.

The team picked one and, following a two-sol break from driving, Opportunity went for it on Sol 4781 (July 6, 2017). The 13.4 meters (43.96 feet) the rover logged that sol took her right over the rim’s edge. After years of wondering, hoping, and then anticipating, the rover had driven the mission into Perseverance Valley – and despite the wheel fright of June, true to her image of being “Little Miss Perfect,” she made it look easy.

Portal to Perseverance Valley
Portal to Perseverance Valley After years of anticipation, Opportunity finally drove over the edge of the Endeavour Crater rim pictured above and into Perseverance Valley in July 2017. Despite an issue with her left front steering wheel in June, the rover made it look easy and promptly hunkered down on a slope to wait out solar conjunction. This view was processed by the Pancam team in false color.Image: NASA / JPL-Caltech / Cornell / ASU

Opportunity drove forward into Perseverance. “Since we managed to straighten the left front wheel, it is safe for us to drive forward using the rear wheels to steer,” said Bellutta. In fact, he added, there are two advantages to having the rover drive forward into the valley. “One reason is that the mast is in front of the vehicle; therefore, we have a better view of the terrain nearby,” he said. “When we point the camera toward the back of the vehicle, anything that is closer than about two and a half meters is only visible is using the Hazcams. But when the rover is facing forward, we can use Navcam and Pancam and have the maximum resolution that you can get with this vehicle.”

The other advantage is that if Opportunity should have to exit the valley for any reason, she would actually be in a better position to drive out backwards. Interestingly, the rover has “a slightly better performance” driving uphill backwards, “because it can climb slightly higher slowly,” Bellutta explained. There is no plan to drive out of the valley, but the rover had not yet passed the point of no return, and just in case, he said, “we want to have that option available to us.”

Opportunity’s arrival inside Perseverance Valley is a huge achievement. But there was no time to celebrate in July. “Everybody was really focused on getting to a northerly tilt and then getting the plans in place to keep the rover safe and toasty and enough to make observations over conjunction,” said Arvidson.

And, Bellutta wanted to take another look at the gentle slope on the southern wall of the valley where the team planned to have the rover park for solar conjunction. “We knew not only from orbital imagery and from previous images taken on the surface that we had a good spot to park the vehicle, but we wanted to recheck that from a different vantage point,” he explained.

Barely inside Perseverance, Opportunity snapped and delivered more images of the chosen knoll. The spot looked just as good from the new vantage point and it was all systems go. And so on Sol 4782 (July 7, 2017) — the 14th anniversary of her launch from Cape Canaveral — the rover that loves to rove put another 13.8 meters (45.27 feet) in the rear view mirror, cruising right up onto the gentle slope. And then she put it in park.

During the previous several weeks, MER Power Team Lead Jennifer Herman had crunched all the numbers and requested that Opportunity settle in for conjunction on a slope of at least 5 degrees to ensure there would be no issues with energy during conjunction. “She wanted at least 5 degrees but 10 degrees would be better,” Bellutta said with a smile. “We try to please Jennifer when we can.”

When the telemetry came down, Opportunity had pushed her odometer to 44.97 kilometers (27.94 miles) and was parked at 9.4-degrees on the knoll, her solar arrays angled toward the Sun. “That is what we wanted and so we were happy,” said Bellutta.

With that, the robot field geologist was in place for conjunction and ready to ride Mars behind the Sun. “We parked early and said, ‘we’re here and don’t want to move,’” said Arvidson. But the robot had about a week and half or so to do some science and look around before the moratorium began. “We were fortunate to have a little bit of broken outcrop under the IDD [Instrument Deployment Device] when we stopped,” said Golombek. “We think the rock is Shoemaker, but we still have some more imaging and analysis to know for sure.”

Opportunity took a well-deserved break on Sol 4783 (July 8, 2017) to recharge and prepare for her next assignments. She woke up late in the evening on Sol 4784 (July 9, 2017) to link up with MAVEN. As long as she was awake, the robot looked to the night sky and took some pictures of the stars, and then measured the argon in the atmosphere with her Alpha Particle X-ray Spectrometer (APXS). 

“The science team is overjoyed of course that the wheel is fixed and very happy that we’re getting on with things,” Golombek said then.

Stars from Mars
Stars from Mars Late in the evening on July 9, 2017, Opportunity focused her Pancam eyes, looked to the night sky, and took some pictures of the stars. This really is a picture of stars from Mars taken by the longest-lived rover ever to explore the Red Planet. How cool is that?Image: NASA / JPL-Caltech / Cornell / ASU

Usually when Opportunity arrives at a new location, the naming theme changes and with the arrival inside Perseverance, it was definitely time. The team voted for the suggestion of MER science team member Larry Crumpler, Research Curator for Volcanology and Space Science at the New Mexico Museum of Natural History and Science, and Planetary Society contributor. So the rover’s targets inside the valley are being named after stops along the El Camino Real de Tierra Adentro, or, in English, the "Royal Road of the Interior Land,” a 2,560- kilometer (about 1,591-mile) long trade route between Mexico City and San Juan Pueblo, New Mexico from 1598 to 1882.

On Sol 4787 (July 12, 2017), Opportunity exercised her IDD for some in-situ or up close and personal contact science from her position on the knoll.  She used her Microscopic Imager (MI) to take the pictures for a large mosaic of a patch of pebbles in front of her and the following sol shot a patch of the terrain with her Pancam, targets the team christened Zacatecas. Following the routine science protocol, the rover placed her APXS on the same targets to glean their chemical compositions.

As the third week of July got underway on Sol 4790 (July 15, 2017), the robot acquired an MI finder frame and then moved her APXS slightly to investigate a cobble within reach, which the team named Parral. “This cobble is adjacent to the more intact broken rock and we think it’s actually representative of what’s there,” said Golombek.

On Sols 4791 and 4792 (July 16, 2017 and July 17, 2017) Opportunity began taking pictures for what will be a multi-frame color image of her conjunction location to be called Tierra Adentro.

With her position on the knoll, the rover was maintaining the ability to produce energy levels upwards of 340 watt-hours despite a solar array dust factor of 0.549. The atmospheric opacity or Tau was fluctuating as usual, but the skies remained pretty hazy and as of Sol 4792 (July 17, 2017) it was recorded at 0.774.

The MER team’s final packet of commands before the solar conjunction were uplinked to Opportunity on Sol 4793 (July 18, 2017), just three Earth days before the moratorium would go into effect on July 22nd. “These commands will keep the rover busy until the team resumes planning on August 2nd,” Bellutta said then.

As Mars disappeared behind the Sun, many of the MER engineers and scientists took a break. “It’s kind of like you’ve sent the kids off to summer camp and now it’s quiet around the house and you can get some things done that you have been putting off for a long while — or you can sleep in in the morning,” as Callas put it.

Endeavour’s west rim and Oppy’s recent roves as of August 2017
Endeavour’s west rim and Oppy’s recent roves as of August 2017 The orbital image of the western rim of Endeavour Crater [left] marks the locations of the raised segments of the rim that Opportunity has visited since arriving in August 2011, plus one. The rover drove into Perseverance in July after nearly two months of surveying the area atop the valley [right]. Annotations for the graphic on the right were meticulously documented by Phil Stooke, an associate professor at the University of Western Ontario, Canada, author of The International Atlas of Mars Exploration Volumes 1 and 2, (Cambridge University Press). The base images were taken by the Context Camera [left] and the HiRISE camera [right] both onboard MRO.Image: NASA / JPL-Caltech / UA / MSSS / P. Stooke

But not everyone took off. A skeleton engineering team would continue to report for work to keep tabs on the fleeting telemetry that Opportunity would downlink and others focused on the sols ahead.

“What is the meaning of vacation?” asked Bellutta. “It is our intention to use this time, when we don’t have a vehicle to drive on Mars, to do some ground testing using the testbed that we have here on Earth to determine if there are some maneuvers that Opportunity prefers or some maneuvers that the vehicle hates in terms of terrain and slope levels on the mechanical structure.”

The plan, said Bellutta, is to run some tests to determine if there are any “corrective actions” that the rover planners (RPs) can take in order to minimize any potential mechanical wear and tear on the vehicle. “We want to be absolutely sure that we treat this vehicle as kindly as possible,” he said. “We want to make sure that this vehicle will drive us around for quite some time.”

Although this solar conjunction would be the MER mission’s seventh, team members spent weeks in preparation, as did team members from the Mars Science Laboratory/Curiosity, and NASA-JPL’s three orbiters Mars Odyssey, the Mars Reconnaissance Orbiter (MRO) and MAVEN. "The vehicles will stay active, carrying out commands sent in advance," said Mars Program Chief Engineer Hoppy Price, of JPL, in a press statement July 14th. "Orbiters will be making their science observations and transmitting data. The rovers won't be driving, but observations and measurements will continue.”

The Mars Relay Office has been through the moratorium drill with all the Mars missions for well more than a decade. “We know what to expect,” said Edwards. “But we take it very seriously every time.”

While Edwards and his crew would exercise their normal relay processes, in the months leading up to solar conjunction, they make sure they and all the missions are ready. “We have a hard look across all the projects and confirm their strategies in terms of communication with the Deep Space Network (DSN), the available relay services, and their readiness,” said Edwards. They especially review how they will use the relay orbiters to continue to support the rovers during that communication outage period.

Since Opportunity would not be driving or using her IDD (robotic arm), the two weeks’ worth of commands the MER team uplinked to their robot were, in essence, a science light campaign. “We put together six plans of 3 sols each to keep the rover occupied through the solar conjunction period,” said Golombek. “The orbiters will still collect data for us during that two week period and will send it all back to us when that two weeks is up.”

Since Opportunity is working in RAM memory however, she must send each sol’s work up to one of the orbiters the same sol before shutting down or it will be lost since RAM is volatile memory. Therefore, the MER team “tuned” the activity level on each sol to be commensurate with the downlink between the rover and the orbiters.

“On the Odyssey sols, we get very limited downlink, averaging maybe 8 megabits a sol,” said Golombek. “There’s also an overwrite issue there too. If we take too much data, then we will overwrite what we took earlier and we have to be aware of that.”

So on the sols where Opportunity is slated to send her data via Odyssey, the plans called for the rover to do an APXS integration on a target within reach and then perhaps take a Tau measurement or maybe one image. “Then every second or third sol, we get an MRO pass and since those passes are in the 40-50 megabit range, we will concentrate on imaging during those sols,” Golombek said.

Groovin’ on a Monday afternoon
Groovin’ on a Monday afternoon Opportunity took this image with her Pancam on Monday, July 10, 2017, shortly after driving into Perseverance Valley. Just to the right of her shadow you can see the deep groove or trough or perhaps channel that greeted her. The Pancam team processed this in false color.Image: NASA / JPL-Caltech / Cornell / ASU

During most solar conjunctions, including this year's, Mars does not go directly behind the Sun. However, almost counts here, like in horseshoes. [Author note: A video showing the Earth-Mars solar conjunction geometry can be found here.]

The Sun's corona, which always extends far from the surface of this humongous, organic nuclear power plant, consists of hot, ionized gas or plasma that can and does interfere with radiowaves that pass through it. “The closer we get to the Sun, the more intense those effects are,” said Edwards.

This time around, Mars will come angularly very close to the Sun as it moves behind it. “We’ll actually come within just over 1 degree between the center of the Sun and Mars as viewed from Earth,” Edwards said. “Once we get inside of about 3 degrees, which happens for about two and a half weeks here, we start to see the effects of this plasma. When we get inside 2 degrees, then the effect becomes significant enough that we’re actually not comfortable sending commands to the spacecraft because we’re worried that they can become corrupted.”

So the mission teams at the Red Planet really have to avoid transmitting for the prescribed two-week period. At least though, the mission team members continue to receive some data, mostly telemetry on the health and status of their spacecraft through the “dark” period of radio silence. But, Edwards cautioned, “loss or corruption of some bits is anticipated.”

For the MER team on Earth, a team that has overcome countless odds and become legendary in its bonding with their robotic colleague, having Opportunity out of sight and out of reach is a little unnerving. Anything can happen. And this time, something did.

Telemetry that Opportunity downlinked on Sol 4797 (July 23, 2017) the MER ops engineers discovered the rover was in automode, the safe state where no master sequence is running and the rover keeps itself calm and cool while waiting further communication from ground control, also known as safe mode.

Zacatecas After settling in on a knoll inside Perseverance Valley, Opportunity used her front Hazcam on July 12, 2017 to take a shadow selfie as she got to work taking close-up pictures of some pebbles with her Microscopic Imager (MI), shown in the image on the right.Image: NASA / JPL-Caltech

“We think that this warm re-set of the rover's computer occurred during the Sol 4795 morning X-band communication session, and that stopped the rover which stopped the stored master sequence of commands, which stopped the work,” said Nelson. “That would have been in the early morning on Friday July 21st Pacific Daylight Time (PDT). By the time this happened, we were in our command moratorium for solar conjunction with no uplink tracks and no plans to try to get any.”

The good news though is that Opportunity is power positive, thermally stable, and will continue to honor the scheduled X-band and UHF relay communication passes through the remainder of solar conjunction. Importantly, the rover is expected to remain safe until her team is able to reach out August 3rd. “We like to say safe mode is safe,” said Edwards. “Right now, that is the safest state the rover can be in.”

As July 2017 shutters, the MER team’s plan is to recover Opportunity first thing on August 3rd. “We’ll just have to pick up and carry on,” said Nelson. All things considered, it’s a safe bet that the rover will stay parked on the knoll long enough to finish the panorama she was to have completed during conjunction.

Since Opportunity works now in RAM mode, the event records or EVRs documenting the warm re-boot are lost, so uncovering the cause will be very difficult to impossible. In the meantime, with no indication that a CME might have caused the sudden stop and start, MER Mission Manager Matt Keuneke and his uplink team are reviewing all the commands on the off-chance an error occurred there.

Despite this latest wrinkle, the MER team, like always, remains optimistic. Cautiously optimistic perhaps, but optimistic. And the plan for the robot field geologist roving forward is the same as it ever was — keep on truckin’.

In Perseverance Valley, Opportunity will be taking hundreds of images so the MER scientists can scrutinize the morphology and other geological elements to test their hypotheses. There’s much work to be done. None of the scientists will commit yet to which theory is the theory with regard to how this valley system was formed, but clearly the unspoken hope is that water, a lot of water was involved.

Perseverance Valley terrain oblique view
Perseverance Valley terrain oblique view In this image taken by the HiRISE camera on Mars Reconnaissance Orbiter, Perseverance Valley is clearly visible just left of center top and as it meanders below the notch or cut in the rim. A false-color image has been draped over topographic data. The relief has been exaggerated by a factor of 2 to help MER scientists better see the valley and the channels that branch from it. In reality, the valley, which stretches for about 200 meters, is actually very shallow, sloping down toward the floor of Endeavour Crater at about 15 degrees. Opportunity stopped roving about halfway down the valley.Image: NASA / JPL-Caltech / University of Arizona

Together with her twin Spirit, Opportunity followed the water, just as NASA wanted. And they uncovered evidence of past acidic water or near-neutral water in rocks and craters, on hills, in grooves and beneath an ancient volcanic site. All of which is evidence that once, a long, long time ago there were environments that were likely habitable on Mars if only teeny tiny microbial life.

And beyond the MER mission, there is an ever-growing body of evidence that Mars has not always been the dry and beyond-freezing cold planet that it is today. In fact, the notion that the Red Planet was once warm and wet and more like Earth – with rivers and lakes, volcanoes and hot springs, and perhaps even an ocean with habitable environments –  has become conventional wisdom.

Perseverance Valley, which was carved, the MER scientists estimate, 3 to 4 billion years ago, during the Noachian Period or maybe the Hesperian Period, could be harboring more evidence for the sought-after liquid gold than any site the MER mission has studied. The whole team is looking forward.

“This will be a somewhat difficult winter, because we have more dust on the arrays than we have had in many of our winters,” noted Nelson. Actually, Opportunity will have to “hop” from one north-facing slope or lily pad to another and then another and so on, if she is to have the power needed to work and drive throughout the harsh winter season.

The valley is shallow, but still, Opportunity will be driving downhill and that limits the view from the ground. “The only concern that I have about the wintertime is that we have limited visibility of the valley,” said Bellutta. “The information from HiRISE indicates that we do have lily pads down into the valley, but we want to make sure that we see these lily pads from the surface. We want to use our vehicle’s camera’s to verify the topography and terrain; therefore, we will be able to project the future path only as far as a drive or two ahead of us.”

The latest power predicts from Herman indicate that if Oppy stays on a 10-degree north slope, then the robot should be able to operate pretty much normally through the winter. “The idea is to maintain our current power levels,” said Golombek. “That is the hope. We don’t want to be stuck in one spot for the whole winter.”

Opportunity’s winter science campaign inside Perseverance will be imaging intensive. The plan for her adventure downslope is to stop on a north-facing knoll every 20 meters or so and take the images needed for a good stereo panorama at each location. That suggests the rover, which will continue, of course, working in RAM mode, will have to spend some time at these stops in order to collect the images needed for the rich, lush panoramas that are a hallmark of this mission – because, as Golombek put it, “we can’t remember anything after we go on to the next sol.”

At the end of the journey though, it will be time well spent. As Arvidson put it: “The 360 Navcams and targeted Pancams collected all the way down for nearly 200 meters will be the dataset gives us the topography and morphology data we want and need to tell us how this whole system actually formed.”

The view from inside Perseverance
The view from inside Perseverance This mosaic scene, which combines five images that Opportunity took with her Navigation Camera (Navcam) on July 7, 2017, shows the rover’s view just after she had driven into Perseverance Valley and onto the small knoll where she waited out solar conjunction. The portion of this scene to the left of the shadow of the rover's mast shows the valley descending to the floor of Endeavour Crater, which is 22 kilometers (13.67-miles) in diameter. Foreground areas in the middle and right sections of the scene show terrain details in the upper end of the valley. The full scene spans from northeast at left to southwest at right.Image: NASA / JPL-Caltech

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