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Jet Propulsion Laboratory
Publication Date: Spring 2005
For decades, ASU planetary geologists and their colleagues had studied Mars from afar, or at least from close orbit. Things changed in 2003. Landing twin robot rovers safely on the Martian surface provided the first thrills. The scientists now have lots of cameras and instruments working on board satellites in orbit around the Red Planet, and more instruments riding around as part of exploration rovers on the surface. The information that those machines have sent back to Earth is astounding.
In the summer of 2003, Mars and the Earth were closer than they’d been in almost 50,000 years. With the planets aligned, two robot travelers left the Earth and began a journey to our red neighbor. On June 10th and July 7th, 2003, NASA launched the Mars Exploration Rovers (MER) from the Kennedy Space Center in Cape Canaveral, Florida. The flight to Mars would take six months.
On board the launch vehicles were twin rovers, two small, solar-powered robots named Spirit and Opportunity. The machines actually are sophisticated, remote-controlled geologists.
Philip Christensen, Jack Farmer, Ronald Greeley, and James Rice have been involved in the MER mission from the very beginning. All are NASA space mission veterans. All are scientists at Arizona State University’s geology department and the ASU Mars Space Flight Facility. They helped to choose the MER landing sites, formulate the mission’s science objectives, and actually designed the instruments that help the rovers search Mars for evidence of a watery past.
Each man happily took part in all the excitement leading up to launch. They dined under a giant Saturn V rocket at NASA’s Kennedy Space Center. And they watched from a moonlit beach as the smaller Delta II rockets lifted their instruments into space.
The ASU scientists set off fireworks in the sand dunes to wish their travelers a safe trip. Also on hand to watch was a large supporting cast of ASU students, both graduate and undergraduate, post-doctoral researchers, and lots of research scientists. Each individual continues to play a role in this momentous expedition.
Summer 2003 was not the typical Florida beach vacation. For all involved, the trip was a prelude to the unprecedented success the rovers would find in the new world the ASU scientists are helping to explore.
Now Arriving…Mars
As of early 2005, the images and information sent back from Mars has been spectacular. There are close-up views of Martian hills and craters. There are images of the dry remnants of a shallow, salty sea. Scenes of bedrock that holds small round rocks nicknamed blueberries. And most importantly, evidence of formerly wet places and watery processes on the planet’s surface.
Both of the rovers have now spent more than a year driving around and working on Mars. They have revealed to scientists Martian landscapes markedly different from anything NASA’s three former landers—two Viking landers in the 1970s and the Sojourner/Pathfinder mission of the 1990s—had ever shown before.
But before Spirit or Opportunity could spin the heads of investigators with their incredible finds, each one had to touch down safely, intact.
The landings were tense moments for scientists. As the critical moment for each landing approached, there was a lot at stake and very little the scientists could do to help.
Light travels fast, but not fast enough to control a Mars rover in real time. Because of the 20-minute delay in sending commands over the great distance between Earth and Mars, Spirit and Opportunity functioned on pre-programmed landing sequences. That data was fed to them by the MER Entry Descent and Landing Team working from the Jet Propulsion Laboratory (JPL) at the California Institute of Technology in Pasadena, Calif.
All the ASU scientists could do was watch and wait. They had to rely on the expertise and ingenuity of the JPL engineers.
Planetary geologist Ron Greeley has been through the pre-landing tension many times before. But that doesn’t stop the butterflies.
“In the moments during the landing, the environment is electrically tense waiting for that single blip indicating success,” he says. “It is also a little strange knowing that the actual landing has already taken place earlier. But we don’t learn the result until later because of the communication travel time from Mars to Earth.”
Greeley has been exploring planets with NASA since the space agency’s first missions to the moon. He has experienced all of the successes and failures of missions to Mars.
“So far the score card is United States 4, the Martians 1!” says Greeley. “Not too shabby considering how difficult it is to land on the surface.”
The MER mission was particularly tense for Greeley. In 1998, he had the agonizing experience of waiting for the signal from the Mars Polar Lander (MPL). That machine crashed on the surface of Mars just before Christmas in 1998.
“It was indeed a bleak holiday season,” Greeley says.
The ASU scientist points out that the MPL crash was especially disappointing because it came on the heels of the loss of another NASA mission to Mars, the Mars Climate Orbiter, earlier that year.
“You can imagine how our apprehension built as Spirit and Opportunity headed for Mars,” he adds.
But the MER landings went without a hitch. The rovers, covered in specially designed airbags, bounced to a stop inside of their pre-determined landing ellipses. They emerged from their protective shells. Each in its turn sent back a success code, the message that it had landed safely. The next transmissions were the images of each rover in its new terrain.
This is when tensions eased and real excitement took hold, says Jack Farmer, an ASU professor of astrobiology. Farmer has been helping NASA develop strategies for the search for life on Mars since 1992.
The MER landings are two of Farmer’s fondest memories from the mission.
“The landings were simply unreal,” he says. “It was like one dream after another coming true.”
With two direct lines safely in place on the surface, Pasadena had become the closest place to Mars on Earth.
Like Greeley, ASU’s Jim Rice had been burned by the 1998 MPL crash. Then a young planetary geologist, MPL was to be Rice’s first NASA mission to Mars.
On January 3rd, during the early morning hours after the successful landing of the Spirit rover, Rice made the first entry in the personal journal he planned to keep throughout the mission.
“We have just landed safely!!” he wrote. “It has been a long hard road to the Red Planet and we have done it. Our team has really done it. We have a lot of challenges and hard work ahead but we are more than ready to take on the job. We just landed a little while ago and we are all celebrating a safe and successful landing!”
Location, Location, Location
With the rovers safely on the Martian surface, it was time for the ASU scientists to get to work. One question had to be answered before anything else could happen—where exactly on Mars were the rovers?
The scientists pored over the first images sent back by the rovers. Speculation began on where they might have landed. They had a general idea because they knew the area in which the rovers were supposed to land. But these were large landing ellipses and relatively small rovers.
“We had betting pools going to predict where we had landed,” Farmer recalls. “We had a big photo of the landing ellipse up on the wall. People stuck pins in the photo to identify where they thought we had landed.”
Using basic geological methods, the scientists eventually converged on their best guesses.
The question was ultimately settled with images from the Mars Orbiter Camera flying high above on board NASA’s Mars Global Surveyor spacecraft. The camera provided incredible high-resolution images.
According to Farmer, nothing had prepared the scientists for what they saw in the photos.
“The images revealed exactly where we had landed. We could actually see both the landers and the rovers,” he says. “But better than that, the images also showed the bounce marks from the air bags that had carried the machines to their final resting spots. And we could see the positions of the heat shields and other entry debris.”
Taking a Look Around
It was in these first looks around the landing sites that Philip Christensen got his greatest satisfaction from the mission. The ASU planetary geologist and his team had predicted before the mission that Opportunity would find the mineral hematite at its landing site, Meridiani Planum.
Christensen and his team are the designers and operators of the thermal emissions spectrometer (TES) flying on board Mars Global Surveyor. Images from TES had pointed to Meridiani Planum as a mineralogically interesting site.
Scientists used TES images to map the minerals present on the surface of Mars. The instrument creates images based on the amount of infrared light that rocks emit when heated by the sun. TES has been orbiting Mars and collecting data since 1997.
At Meridiani, TES saw something that was unusual on Mars. Most of the rock on the surface of Mars is volcanic. It shows little or no sign of ever having been affected by water.
Meridiani Planum doesn’t look like much in visible photography. The word ‘planum’ means plane. That is exactly what the area is—a large, flat expanse. But viewed in the infrared with TES, Christensen and his colleagues saw the mineral hematite. That grabbed their attention, big time.
Why the big deal? The ASU scientist explains that hematite is a mineral that forms almost exclusively in wet environments. Christensen and his team interpreted this to mean that Meridiani Planum may have once been a lake. Based on this interpretation, the MER team selected Meridiani as Opportunity’s landing site.
Spirit’s landing site was at Gusev Crater. That area had been studied for years. In visible images, it looked like a good landing site. It appeared as though an ancient river channel had once flowed into the crater.
Gusev Crater contained what looked like shorelines, deltas, and other features associated with flowing water. Soon after Spirit landed, it didn’t take the scientists long to realize that they were, as Farmer recalls, “sitting on a younger lava plane.”
Says Farmer, “If water-deposited sediments were present, they were likely buried beneath some unknown thickness of basaltic lava.”
The visible evidence had not immediately panned out.
When Opportunity arrived at Meridiani, Christensen and his team went to work. He wanted to show that infrared mineralogy could provide success where visible evidence had failed. Both rovers were equipped with an instrument called Mini-TES, a smaller version of TES.
Christensen used Mini-TES to look for the hematite that TES had predicted should be present. He would not be disappointed.
Christensen’s favorite moment from the mission is the night he presented the first Mini-TES data to the rover science team.
“I had slept four hours in the past 48,” Christensen explains. The temperature sensors on the rover deck that were supposed to be used to calibrate Mini-TES had failed. Christensen had lost sleep completely rewriting the Mini-TES calibration software.
“It took three weeks to write this software the first time. I had to rewrite it in less than two days,” he says.
But these trials only made the final presentation of the Mini-TES data sweeter for Christensen.
“It was the first real Mini-TES data ever presented. It was early in the morning, and everyone was running on adrenaline,” he continues.
The Mini-TES results were exciting. Soon after this initial presentation, and again early in the morning, Christensen presented the results a second time—this time to a crowded auditorium filled with reporters.
“We were able to show that we really had landed in a sea of hematite,” says Christensen.
It was 4 a.m., but the early hour didn’t put a damper on the excitement. As the media members applauded, the rover team cracked open a bottle of champagne to celebrate the results.
The Mission Continues
The landings and the initial findings of Spirit and Opportunity are prominent in the memories of all the ASU scientists and staff members involved. But the mission continues.
Both Mars rovers have lasted much longer than their intended 3-month lifespan. And both have performed far better than expected.
According to Greeley, “After more than a year in operation, both rovers have demonstrated that it is possible to carry out sophisticated studies of another planet through robotic operations.”
Following is a brief summary of the sophisticated studies the Mars Exploration Rovers have carried out to date.
Opportunity bounced and landed inside a small crater that the scientists named Eagle Crater. The crater contains bedrock—rock that actually sits where it was initially deposited during the planet’s formation eons ago. This is the first bedrock that scientists have ever seen on Mars. Every earlier mission had only explored rocks that had been moved to their current positions by explosive forces.
The bedrock Opportunity found set the tone for the mission as it has unfolded. The finding also influenced the way Spirit has gone about its work. Spirit was sent looking for bedrock near its landing site.
To date, Spirit has done quite a bit of traveling. When scientists found it difficult to find sediments on the surface of Gusev Crater, they set their sights on finding the nearest large crater within Gusev. This took the rover to a crater they named Bonneville.
Unfortunately, the impact that formed Bonneville did not punch deep enough through the lavas to expose the lake sediments. Spirit was again sent on the move.
In a bold strategy, the scientists sent Spirit to traverse a 2.5 kilometer distance toward the Columbia Hills. There they hoped to find an older record of water-related processes. At the Columbia Hills the scientists found their elusive outcrops.
“Against all odds we made it to the top of the hills,” Farmer explains. “We now are trying to decipher the history of what are very likely water-influenced deposits.”
The exact origin of these older deposits is not yet understood. However, looking at the minerals, the scientists are certain that water played an integral role in their origin.
Though it landed in a sweet spot, Opportunity has done its share of moving as well. Using Mini-TES and the other spectrometers and instruments onboard, scientists determined the origin of the hematite in Meridiani Planum.
The hematite had been predicted from orbit and served as a beacon to the scientists. However, none of the predictions about its formation did justice to the geologic complexity that Opportunity actually found. The hematite appears to have been formed after the deposition of sulfate-rich lake deposits.
Says Farmer, “It just shows that it is hard to second-guess Nature!”
From Eagle Crater, Opportunity has moved on to Endurance Crater, tracking outcrops of bedrock as it rolls along. Farmer has been planning missions to Mars with NASA since 1992. He couldn’t be more pleased that these sulfate-rich lake deposits have become the focus of MER research.
“The evaporate-lake environment is identical to one of the major environments I have been promoting in the search for life on Mars in the last two decades,” he says. “Imagine my surprise when we landed on exactly one of these types of deposits. Now I have the privilege of studying these rocks with an incredibly talented group of people. It was and is the chance of a lifetime.”—Matthew ShindellPlanetary geology research being conducted on Mars and in other portions of the solar system by ASU scientists is supported by NASA, the National Science Foundation, and other funding agencies.Physical Science: Space Science