Two untouched photographs from Martian days 3528 and 3540 of Opportunity's mission. The "jelly doughnut"-sized rock in the center of the photograph to the right is the mystery rock.
Image: Curiosity's tire tracks from its first
Alien Robots That Left Their Mark on Mars
Aug. 24, 2012 --
Since the dramatic powered landing of NASA's Mars Science Laboratory (MSL) on Aug. 5/6, the one-ton rover has achieved a number of "firsts." It was the first planetary mission to use the exciting Sky Crane maneuver; the first to shoot lasers (for science); it's even the first nuclear-powered rover to put tread marks into Martian dirt. But it certainly isn't the first rover on the Red Planet -- two generations of Mars rover came before it. And the numerous stationary landers have also left their mark. To any hypothetical Martians on the Red Planet, it may look like an alien invasion is underway -- but these aliens come from the Blue Planet and they seem to insist on sending wave after wave of increasingly sophisticated robotic probes that dig, burn, scour and damage their pristine landscape! So, as we watch the incredible Curiosity rover dominate Gale Crater, it's time to take a step back and contemplate how these surface missions have changed the Martian landscape.
Image: Sojourner investigates a rock a short
The First Rove As we ooh and aah over Curiosity's plus-sized wheel marks, it's time to turn the clock back to 1997 when a 2-foot long wheeled robot made its first, tentative sojourn onto Mars. NASA's Mars Pathfinder mission was the first successful rover mission to the Red Planet (the first attempts were the Soviet Mars 2 and Mars 3 surface missions in 1971 -- both failed) that saw the Sojourner rover explore its landing site for over 80 days after landing on July 4. Its primary mission was only seven days. The little rover left behind plenty of tire tracks that likely persisted for some time after the mission concluded -- they probably quickly became filled with Mars dust and eroded by winds.
Credit: NASA/JPL-Caltech/University of Arizon
Orbital Tracks The immensely successful Mars Exploration Rover (MER) Opportunity is in its ninth year of operations since landing on Mars on Jan. 25, 2004. As the rover continues to explore the Red Planet, notching up over 20 miles on the odometer (so far!), it has also left an impressive history of tire tracks. Amazingly, these tracks can be seen from orbit and NASA's Mars Reconnaissance Orbiter (MRO) has been able to keep a close eye over its roving cousin from space using its High-Resolution Imaging Science Experiment (HiRISE) camera. In this orbital snapshot, Opportunity can be seen at the edge of Victoria Crater (in 2006), plus wheel tracks. Like Sojourner, these tracks are not permanent, Mars' weather will erode them over time. So it's fortunate that Opportunity is still roving, creating new tracks.
Image: A photograph by Spirit shows the obvio
Trench Digging MER Spirit, Opportunity's ill-fated sister rover, also surpassed her "warranty" by five years after landing on Mars on Jan. 4, 2004. Sadly, after becoming immobilized in a sand trap inside Gusev Crater in 2009, rescue attempts failed and the rover was confirmed lost after it stopped transmitting in March 2010. Spirit didn't travel as far as Opportunity -- logging nearly 5 miles -- and had a harder time on the surface of Mars. Early in the mission on March 13, 2006, one of the rover's wheels ceased working, forcing rover drivers to drive Spirit backwards, dragging the dead wheel behind it. Serendipitously, the frozen wheel became a handy trench-digger, creating a deep groove in the loose top soil as it roved. Material that would have otherwise been inaccessible could be glimpsed. Spirit's roving tracks will therefore likely remain visible on Mars for some time to come due to a sticky wheel.
Image: One of the Rock Abrasion Tool (RAT) ma
Branding Rocks But it's not just tire tracks Spirit and Opportunity left on Mars, they have created a rather more permanent calling card. Using the rock abrasion tool mounted to both rovers' robotic arms, the wheeled robots have scoured the surface layers off a number of rocks for scientific study. On each rock, a 45 millimeter diameter circular "branding" has been left behind.
Image: The view of a rock plus fresh laser sc
Laser Tattooing Rocks Although tagging rocks with circles is certainly cool (and of high scientific merit), the new rover on the Mars block has been outfitted with an instrument to laser-blast rocks with. Curiosity's ChemCam instrument mounted atop its mast can shoot rocks at a distance with a powerful laser beam, burning the surface layers. The resulting flash of light contains information about the rock's constituents, which ChemCam analyzes. Like Spirit and Opportunity, Curiosity can leave its own calling card -- a tiny, permanent laser'd tattoo.
Bouncy Bouncy Landing on Mars is serious business, and some very inventive methods have been used. The 1997 Mars Pathfinder mission, for example, touched-down with a bounce -- airbags were deployed, ensuring a cushioned impact with the ground after descent through the atmosphere. Airbags were also deployed during the landings of Spirit and Opportunity in January 2004. In this photograph, Opportunity retraced its bounce-marks to see impressions of the airbags preserved in the Martian regolith. The bags' seams can be seen. As the airbag bounce only imprinted the uppermost surface, it's likely these impressions were rapidly blown away and/or covered with dust.
Image: Two craters formed by Curiosity's rock
Rocket Excavation Of course, Curiosity has to go one-better than its predecessors. During the powered landing of the rover, the Sky Crane's rocket-powered assembly delivered a huge amount of thrust to make sure Curiosity had a soft landing (air-bags aren't a viable landing method when delivering a rover the size of a car). Although debris was blown atop the rover, potentially damaging a wind sensor, the maneuver was a resounding success. But evidence of the landing has been spied around the rover. Areas of excavated material, creating shallow craters, surrounded the rover after landing. This ended up being a fortuitous event -- loose surface layers of dust and gravel were blown away, exposing the bedrock of Gale Crater. The bedrock has been the focus of study and the craters will likely be some long-term scarring of the Martian surface.
Credit: NASA/ JPL-Caltech
Crash and Burn Although the Sky Crane landed Curiosity safely to the surface, the rocket-powered platform suffered a messy demise. After its job was done, it throttled-up and flew far away from the rover, ditching into the Mars landscape. This HiRISE image shows the carnage that the Sky Crane's mass left behind after impact -- a site to remember the Sky Crane's good work.
Credit: NASA/JPL-Caltech/University of Arizon
Man-Made Meteorites Shortly after Curiosity entered the Martian atmosphere, as it began its descent, the rover's aeroshell (a capsule composed of a heatshield and backshell) jettisoned six 55-pound (25-kilogram) tungsten slugs to improve its stability as it used the Martian atmosphere to steer to its target. These ballast slugs slammed into the Martian surface -- basically man-made meteorites -- and could be spotted from orbit.
Image: Phoenix's scoop it used to excavate th
Phoenix With all the excitement surrounding rovers, it's about time to remember the not-so-mobile Mars explorers. On May 25, 2008, NASA's Phoenix Mars Lander touched down in Mars' arctic region to carry out experiments in a region we know little about. Using its arm-mounted scoop, the lander was able to retrieve samples from the freezing ground, dropping the material into its chemical laboratory for analysis. Phoenix made the landmark discovery of perchlorate in the soil and found water ice (that slowly sublimated) in the uppermost layers of the permafrost. Although Phoenix was never going to last long -- the arctic winter most likely cocooned the robot in ice. By Nov. 2, 2008, the mission was declared lost. Surrounding the landing site, however, small trench marks will likely remain -- remnants of Phoenix's science.
Image: The view from Viking 1, with trenches
The Trendsetter NASA's first landers also left their mark on Mars. The Viking landers were hugely successful, returning the first images from the Martian surface and carrying out a suite of experiments to directly search for microbial life. Viking 1 lasted from July 1976 to November 1982; Viking 2 lasted from September 1976 to April 1980. To this day, the Viking experimental results are debated, but the deep trenches that were dug likely remain behind. MORE: Mars Curiosity 'Litter Bug' Spied from Orbit: Photos
NASA's Opportunity rover spotted an odd Martian rock that looked like a doughnut on Jan. 8. Four days earlier, however, the rock wasn't there at all. So how did the rock appear? Alien rock throwers? A nearby meteorite impact?
The truth is much less surprising. Scientists working with the intrepid robot have just confirmed that the rock (called Pinnacle Island) was simply kicked up by one of Opportunity's wheels as it made its way across the planet's surface. [Amazing Photos from NASA's Opportunity Mars Rover]
"Once we moved Opportunity a short distance, after inspecting Pinnacle Island, we could see directly uphill an overturned rock that has the same unusual appearance," Opportunity deputy principal investigator Ray Arvidson, of Washington University in St. Louis, said in a statement. "We drove over it. We can see the track. That's where Pinnacle Island came from."
The rock stirred up enough controversy that a concerned citizen even filed a lawsuit against the space agency, claiming that NASA failed to properly investigate a possible fungus growing on the Red Planet.
Although researchers figured out where the rock came from, there are other weird aspects of the Pinnacle Island tale. Using Opportunity's tools, mission scientists have discovered that the rock has very high levels of sulfur and manganese. Both of those elements are water-soluble, suggesting that they were concentrated in the rock due to the "action of water," NASA officials said.
"This may have happened just beneath the surface relatively recently, or it may have happened deeper below ground longer ago and then, by serendipity, erosion stripped away material above it and made it accessible to our wheels," Arvidson said.
The rock is located in a spot on "Murray Ridge" along the wall of Endeavour Crater, where Opportunity is spending the Martian winter. Now that the rover is done examining Pinnacle Island, the Opportunity team is planning to drive the rover uphill to check out exposed rock layers on a different part of the Martian surface.
"We are now past the minimum solar-energy point of this Martian winter," Opportunity project manager John Callas, of NASA's Jet Propulsion Laboratory in Pasadena, Calif., said in a statement. "We now can expect to have more energy available each week. What's more, recent winds removed some dust from the rover's solar array. So we have higher performance from the array than the previous two winters."
Opportunity has been exploring Mars since 2004, landing on the Red Planet a few weeks after its twin, Spirit, touched down on the Martian surface. Both rovers were assigned 90-day missions, but Spirit gathered data until 2010 and Opportunity is still roving along.
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