Spirit Discovers Surprises in Martian Soil, but Earth Weather Blocks Commands to Continue Work
Spirit got off to a running start this week, using three of the four instruments on her robotic arm to study a patch of Martian soil, and the football-sized rock Adirondack. But thunderstorms and rain around a Deep Space Network (DSN) radio dish in Canberra, Australia early this morning blocked the uplink commands for her to deploy the Rock Abrasion Tool -- the RAT -- and grind into the rock.
Then, late in the day today, the Jet Propulsion Laboratory (JPL), which designed and built the Mars Exploration Rovers, issued a press release reporting "an unresolved issue" with the status of the rover.
While ground controllers were able to send commands to Spirit early today and received a simple signal acknowledging the rover heard them, they did not receive expected scientific and engineering data from the rover during scheduled communication passes during the rest of that Martian day, the release stated. Project managers have not yet determined the cause, and the mission team is examining a number of different scenarios. The release noted that "similar events occurred several times during the Mars Pathfinder mission."
In any event, Spirit is safe and sound. When it failed to receive the uplinks this morning, it automatically shifted into a kind of safe mode. "The morning timeframe, local solar time at Gusev between 9:00 a.m. and 9:45 a.m., is an important time for us to take commands and transmit commands to the rover," explained Jennifer Trosper, Spirit mission manager, at the daily news briefing this morning. "[The rover] will start to act on those [commands] around 9:45 a.m., local solar time. Because of the rain in Canberra, we were not able to transmit the commands. [Spirit] received a weak signal from Earth because of the rain, so it didn't get all the data we wanted it to get."
As a result, Spirit did what she "was supposed to," Trosper said. The rover went into what is called a 'master sequence,' a mode that "takes care of the rover," keeping it awake during day, but not attempting any movements with her robotic arm or driving. "Not a lot of science was done today, but rover is in a very safe state, very comfy, and now we're waiting on communications from Odyssey.
Although the forecast for Canberra calls for rain over the new few days, the mission team hopes to command Spirit to use the RAT and grind into Adirondack, sometime in the next couple of days, provided her "unresolved issue" gets resolved.
While Spirit continued the master sequence that automatically puts it to sleep for the night, the team on the ground this morning presented a crisp, remarkably detailed image of Columbia Memorial Station, a mosaic of 12 smaller images that the rover took with its stereo, color Panorama Camera. Although it has not yet been put through the final phases of color balancing, the image is nothing less than impressive and reveals virtually all of the highpoints on this mission so far.
"This is an image that captures our solemn feelings toward the astronaut crew to whom the Columbia Memorial Station is dedicated," said Randall Lindemann, mechanical subsystem engineer for Spirit. "In this image, we see both the starting point of Spirit's mission -- the cradle of this exploration, namely the lander . . . the near rim of the large crater, which is about 250 meters away from the lander location, where the team would like the rover to go towards for roughly the mid-part of the surface operation mission. And finally at the upper right hand corner of the image, we see the north end of the East Hills complex, [where] the team would like the rover to head toward in the latter part of the mission and end its mission there if possible."
Despite the "unresolved issue" of today, the Mars Exploration Rover has completed in situ measurements on the soil, and on Adirondack, this week, as well as taken some microscopic images of the rock.
Early Tuesday morning -- Sol 16 for Spirit on Mars, the robot field geologist took measurements from a patch of soil directly in front of her with the Mössbauer spectrometer and the alpha particle x-ray spectrometer (APXS), both of which were brought to the MER project by Germany. Each of these instruments determines the composition of soil and rocks, but in different ways.
Late Tuesday evening and early this morning -- Sol 17, Spirit used the Mössbauer spectrometer on "an overnight integration" on Adirondack for "her first real look at a Martian rock," as the principal investigator for the suite of instruments on Spirit and Opportunity, Steve Squyres, put it at the morning news briefing yesterday. "We are starting to put together a picture of what the soil at this particular place in Gusev Crater is like," Squyres said. "There are some puzzles and there are surprises."
The mighty Mössbauer
The findings that Spirit returned from the Mössbauer spectrometer early yesterday morning presented scientists with a couple of surprises and new puzzles to solve.
Since scientists believe that many of the minerals on Mars contain iron, the Mössbauer spectrometer was designed to determine the composition and abundance of iron-bearing minerals that are difficult to detect by other means. By identifying iron-bearing minerals, scientists can learn more about Gusev's early environmental conditions, which is part of the mission's goal.
The Mössbauer -- which uses two pencil-eraser-sized pieces of radioactive cobalt-57 as the radiation sources -- is also capable of examining the magnetic properties of surface materials and identifying minerals formed in hot, watery environments that could preserve fossil evidence of Martian life.
To operate the Mössbauer, Spirit deploys her arm and the device, pressing the flat, contact plate directly against the chosen patch of soil. "Each mineral has its own distinctive Mössbauer pattern, like a fingerprint," explained the lead scientist for this instrument, Goestar Klingelhoefer, of Johannes Gutenberg University, in Mainz, Germany. When the data is returned to Earth, the measurements are displayed in graphs as peaks, with the most abundant mineral boasting the tallest peak.
One unexpected finding from Spirit's Mössbauer measurements was its detection of a considerable amount of olivine in the soil, a silicate mineral that is made up of silicon, oxygen, iron, magnesium. In fact, there was more olivine registering than any other single material. "It is the kind of mineral that one finds in igneous rocks, volcanic rocks, lava, and basalt," Squyres explained. Although olivine actually forms in a number of different rocks, it is, for the most part, a primary igneous mineral. "It is not something that you form as a result of lots of chemical weathering," he pointed out.
"We were surprised about finding olivine in the soil, because we expected weathering material like iron oxides and we haven't seen this yet," Klingelhoefer told The Planetary Society later. " We expected to see a little bit of olivine, which is usually around from the rocks, but this amount was a little bit of a surprise."
What exactly does that mean?
The science team currently has multiple working hypotheses on the table. "There are a couple of different ways of interpreting this," Squyres noted. The lack of weathering indicated by the presence of olivine might be evidence, he suggested, that the soil particles are finely ground volcanic material. "One possibility is that this Martian soil, rather than being the result of a chemical weathering process is simply very finely ground lava, very finely ground rock. That would be a surprise to me."
Another possible explanation is that the soil layer where the measurements were taken is extremely thin, and the olivine is actually in a rock under the soil. Some members of the science team, in fact, are "so surprised" to see the olivine in this measurement, "that they don't think we're looking at the soil," Squyres said. "It's entirely possible that that one to two millimeters down beneath those grains is solid rock and [these] people believe that what we're seeing is through that fluffy stuff." The Mössbauer uses "gamma rays that can penetrate -- if it's fluffy -- a few millimeters of stuff, so there may be solid rock underneath this," he noted.
"We're not quite sure what's going here, but we have the tools to test it [more]," Squyres pointed out. "We can scrape. We can dig with the wheels. The key here is that we're starting to put together a comprehensive picture of what this stuff looks like -- and this is just our first patch of dirt."
The science team was also surprised by how little the soil was disturbed when Spirit's robotic arm pulled off the Moss Bauer’s contact plate from the patch being examined. Microscopic images from before and after that pressing showed almost no change. "I thought it would scrunch down the soil particles," Squyres said.
"What I was suspecting was that these thing were held together by electrostatic forces -- static cling -- little, very weak, electrostatic forces that holds together grains. And what I thought was going to happen was that the first time we scrunched this stuff down, the first time we pushed on, those things would just collapse, flatten like talcum powder . . . didn't happen. Nothing collapsed. What is holding these grains together?"
That remains a mystery at the moment. But, Squyres proffered: "There may be sulfates and chlorides binding the little particles together," types of salts could be left behind by evaporating water, or could come from volcanic eruptions."
The highly sensitive APXS
Data garnered from another instrument on Spirit's arm, the alpha particle X- ray spectrometer (APXS), may offer up the clues needed to unravel that mystery.
The APXS -- a small instrument, which uses alpha particles and x-rays to examine the surface of soils and rocks just down to 10 micrometers -- has revealed that the surface of the chosen patch of soil is made up of silicon, sulfur, chlorine, and argon. That synchs nicely with the characteristics of soils studied at previous Martian landing sites -- the Mars Pathfinder site, as well as the two Viking sites -- but is unlike soil composition on Earth. However, the technology has improved since those earlier missions and this model APXS has detected other minerals never found before found on Mars.
"This instrument is so sensitive that we can now detect nickel and zinc on the Martian surface which has not been done before," noted MER science team member Johannes Brueckner, from the Max Planck Institute for Chemistry, Mainz, Germany. Although the copper detected "comes from our instrument itself," the nickel and zinc are Martian. "This sensitivity will help us to monitor even minor changes in chemistry on all future soils and rocks which we hopefully measure."
"We have an enormous capability to sample a huge range of depths with this vehicle," added Squyres. "We can sample depths anywhere from 10 microns to 50 meters -- and the way we do 50 meters is we use the [rover's] wheels -- and we drive through a crater - hey, Mother Nature dug holes, man -- use them. So we put this payload on a rover for a darn good reason and that is the ability to move around and take advantage of the topography that Nature's given us."
Not from around here?
It may be that the stuff Spirit is looking at didn't come from around Gusev proper. In other words, the soil may not have even originated anywhere near Spirit's landing site. "Mars has these global dust storms where huge amounts of dust get lofted into the air, and get distributed globally over the whole planet and then eventually settle out -- that's a process that stirs up stuff and homogenizes it over the entire planet, so this stuff could have come from somewhere else."
The soil may not have even originated anywhere near Spirit's landing site, because Mars has dust storms that redistribute fine particles around the planet. The next target for use of the rover's full set of instruments is a rock, which is more likely to have originated nearby.
"Mars has these global dust storms, where huge amounts of dust get lofted into the air, get distributed globally over the whole planet, and then eventually settle out -- that's a process that stirs up stuff and homogenizes it over the entire planet, so this stuff could have come from somewhere else," Squyres explained. "It's going to be very interesting to start digging some holes and seeing if it looks the same beneath the surface. Or to go to someplace else, where Mother Nature has dug some whole -- craters -- and see if it looks the same there. So we don't even know if this stuff came from Gusev, but we're learning a lot about it."
For now, the science team will continue working with a number of different hypotheses about what is going on in the Martian soil at this particular location. "And we're trying to figure out which one is right," said Squyres. "These observations, preliminary as they are, have revealed some very interesting things about this soil and have posed some new questions for us to pursue in the weeks and months ahead."
Spirit's mission is to examine rocks and soil for clues about whether the past environment there was ever watery and possibly suitable to sustaining life. While the clues needed to determine whether Gusev Crater was once a lakebed may be elusive at the moment, Squyres, for one, is convinced it had to have once contained a large body of water and that Spirit has what it takes to prove it.
"I don't think there's any question that there was once a lake in Gusev Crater, but I have also said Mars is not going to give up her secrets very easily and finding those materials is going to take the full capabilities that this vehicle has to offer. It's going to take a long time to puzzle through this, but the key is we've got the tools to do it as is shown by these [Mössbauer and APXS] spectrum."
In the meantime, the debates about what they're seeing rave on backstage and even in the press briefings. When asked if there was any place on Earth where the soil resembled what scientists have seen so far at Gusev, Squyres turned to Dick Morris, a science team member and expert in soil chemistry, who was sitting with the journalists.
"There are many places in Hawaii that look exactly like this," Morris said. "Hawaii is a basaltic world, just like Mars, and there are beaches and volcanic areas like Mona Kea that have not only the same basic basaltic composition, but are denude of vegetation and look just like Mars."
But Ben Clark, another member of science team and a veteran of the Viking missions, countered: "Back when we got this first unique sulfur chlorine composition from the Viking results, we went around for a few years challenging people to bring us a sample that gave us the same signature. That was 30 years ago. I've yet to see a soil sample that matches Mars exactly or even really close with this particular profile of elements."
"The response to that is that the Earth has a lot of rain that washes that stuff into the ocean and Mars doesn't," rebutted Morris.
"This is why it's so much fun to run this science team," Squyres chuckled.
While the debates go on, the data are now coming down and being presented "hot off the spacecraft," as mission manager Jennifer Trosper put it yesterday. Odyssey, for example, was able to return 99 megabits of data Monday night. "That's just an incredible amount of data coming through the link -- it's like we got an upgrade to our Internet connection last night."
This near real time transfer makes the Mars Exploration Rover mission different from its predecessors in that scientists can make and/or adjust their plans rapidly, as findings come in. But weather can and did interrupt that flow of information today.
"This [is] something that is kind of typical of spacecraft operations," Trosper pointed out. "There are days when it rains and things don't quite go the way you expected. But the rover is healthy and depending on what we see on UHF pass, it's possible we'll wait to get all the data before we move on with the RAT-ting activity, so it's possible we would RAT tomorrow and it's also possible we'd wait one more day."
Spirit, meanwhile, has cooled off a bit now that it is off the lander, just as the mission team had predicated and that means her workday has gotten longer. "We're able to stay awake a little bit longer and accomplish some more science in the afternoon," Tropser said. In addition, she said that the rover's power situation is looking good. "We are mostly constrained by the amount of data we can collect and get on board the spacecraft and that's a great constraint to have."
In fact, the most unexpected thing to date, Trosper said was not the missed connection today, but how just how impressive Spirit's operations have been. "A lot of my involvement in this project has been in system engineering and the verification and validation of the vehicle, and I think the thing that is just a great tribute to all of the people who have worked on the project is how well the rover works -- and not just in specific instances," she said. "All through cruise, we had no problems with the vehicle. Entry, descent and landing went just like we expected it to. The impact to egress [brought on] some “poofy” airbag issues, but in general, the hardware, the software and teams that process the tools -- they're working, and we're moving much faster towards the science objectives that we ever anticipated.
"If you go back to the beginning of this mission, [when we talked about] what we could accomplish over course of 90 days, based on Pathfinder experience and on what the people who had worked Viking and other Mars missions had to say, we [figured] one in every three days something will go wrong -- rain in Canberra, problem with a tool, something so that [we weren't] going to accomplish what we intended to accomplish," Trosper continued. "Today we're 17 for 18 and that makes me very proud and surprises me a little bit."
Spirit landed in Gusev Crater on January 3 Pacific Standard Time (on January 4 Greenwich Mean Time). Her twin, Opportunity, is on target to touch down in Meridiani Planum, on the opposite side of the Red Planet from Spirit, at 9:05 p.m. PST, this Saturday night / early Sunday morning Easter Standard Time and Greenwich Mean Time, to conduct a similar geological field study of that site.