Tucson, Ariz. -- A Martian rock resembling a jelly doughnut was broken and displaced when NASA's Mars Exploration Rover Opportunity drove over it, researchers operating the rover have determined.
Only about an inch-and-a-half (4 centimeters) wide, the white-rimmed, red-centered rock, dubbed "Pinnacle Island," caused a stir last month because it showed up in an image the rover took on Jan. 8, 2014, at a location where this rock was not present four days earlier. Newer images show the original piece of rock the rover wheel hit, slightly uphill from where Pinnacle Island came to rest.
James Rice, a Planetary Science Institute Senior Scientist and rover team member, pinpointed precisely when Pinnacle Island was emplaced.
“When Pinnacle Island was first surprisingly discovered the time interval reported was that it occurred sometime between sols 3528 and 3540, a period of 12 sols, or Martian days,” Rice said. “I continued image analysis of this region and discovered that the time interval for the emplacement of this interesting rock was actually only 4 sols, between Sol 3536 and 3540. This was important because it allowed us to narrow down the search region for where this rock came from and what rover motion was responsible.”
"Once we moved Opportunity a short distance away after inspecting Pinnacle Island, we could see directly uphill an overturned rock that has the same unusual appearance," said Opportunity Deputy Principal Investigator Ray Arvidson of Washington University in St. Louis, Mo. "We drove over it. We can see the track. That's where Pinnacle Island came from."
High levels of elements such as manganese and sulfur in Pinnacle Island suggest these water-soluble ingredients were concentrated in the rock by the action of water. "This may have happened just beneath the surface relatively recently," Arvidson said, "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."
Now that the rover is finished inspecting this rock, the team plans to drive Opportunity farther south and uphill to investigate exposed rock layers on the slope.
A boulder-studded ridge the rover will be approaching has been given an informal name honoring two engineers who on Feb. 14, 1969, risked their lives to save what turned out to be NASA's second successful Mars mission, Mariner 6, on its launch pad. The "McClure-Beverlin Escarpment" commemorates the late Bill McClure and Jack Beverlin. Their quick action to tend valves as the Atlas-Centaur launch vehicle began to crumple from loss of pressure earned them the first NASA Medal of Exceptional Bravery.
"Our team working on Opportunity's continuing mission of exploration and discovery realizes how indebted we are to the work of people who made the early missions to Mars possible, and in particular to the heroics of Bill McClure and Jack Beverlin," said PSI’s Rice. " I have been in contact with the families and they are overjoyed with this honor. The story of how McClure and Beverlin saved the Mariner 6 Mission and risked their lives is very remarkable and needs to be told. We felt this was really a fitting tribute to these brave men, especially with the 45th anniversary of their actions coming today."
Opportunity's planned work on the north-facing slope below the escarpment will continue to give the vehicle an energy advantage by tilting its solar panels toward the winter sun low in the northern sky. Today, Feb. 14, is the winter solstice in Mars' southern hemisphere, which includes the Meridiani Planum region where Opportunity has been working since landing in January 2004.
"We are now past the minimum solar-energy point of this Martian winter," said Opportunity Project Manager John Callas of NASA's Jet Propulsion Laboratory, Pasadena, Calif. "We can now expect to have more energy available each week than we did the week before. What's more, the rover has experienced recent wind events that removed some dust from the solar array, and we now have higher performance from the array than in either of the previous two winters."
During Opportunity's decade on Mars and the 2004-to-2010 career of its twin, Spirit, NASA's Mars Exploration Rover Project has yielded findings of a range of wet environmental conditions on ancient Mars -- some very acidic, others milder and more clement for possible life, if Mars has ever supported life.
Rice’s research is funded under a subcontract to the Planetary Science Institute from the Jet Propulsion Laboratory/California Institute of Technology, which manages Mars Exploration Rover.