Title: Fond Farewell to Spirit, the first Martian Geologist
Author: Ira Pasternack
Publication: The Outcrop, July 2011, p. 12-15
Article Type: President’s Column
I was very sad to read the May 24th 2011 NASA JPL press release that stated attempts to contact the Mars Exploration Rover (MER) named “Spirit” had failed to reawaken the rover and no further attempts to communicate were being made. Spirit had finally succumbed to the frigid Martian winter when there was insufficient sunlight for the rover’s solar panels to maintain the battery’s charge that provided energy to run heaters necessary to survive the bitter sub 60-degrees-Fahrenheit-below-zero cold. The last communication with Spirit was on March 22, 2010, after the rover had broken through an unseen hazard and became embedded in unconsolidated fine material. It is remarkable that Spirit lasted over 6 years and drove over 7.7 km (4.8 mi) when the original MER design specifications stipulated a 3-month mission with a kilometer traverse capability.
Spirit and the twin rover, “Opportunity,” were the first spacecraft to successfully conduct robotic geologic studies on another planet. The rovers were launched about a month apart, with Spirit’s send-off on June 10, 2003 and Opportunity on July 7, 2003. Spirit landed on Mars January 3 PST, 2004 while Opportunity landed January 24 PST, 2004. Among the two rover’s primary scientific goals was to search for rocks and soils that held clues regarding water’s history on Mars. It was thought that if life ever evolved on Mars, it probably did so in the presence of a long-standing supply of liquid water. The rovers targeted sites on opposite sides of Mars that appeared to have been affected by water in the past.
Spirit’s landing site was Gusev Crater, a possible former lake in a giant (160 km- or 100 mi-wide) impact crater. Gusev is located at the outlet of a very large dry river channel that is hundreds of miles long. It was hoped that the crater had collected sediments from a variety of sources during its 3.9 Ga history, including fluvial, lacustrine, volcanic, glacial, impact, regional and local eolian and global air falls (Cabrol, et al., 2003).
Meridiani Planum was the landing site selected for Opportunity because a layer rich in the iron-oxide mineral hematite was detected there by a spectrometer on the orbiting Mars Global Surveyor spacecraft (Christensen, et al., 2005). Under most circumstances on Earth, hematite forms in association with liquid water. There are processes under which hematite may form without water being involved, but this was considered a reasonable risk when the Meridiani Planum site was considered.
The primary scientific instruments carried onboard both rovers included:
Panoramic Camera (or “Pancam”): for determining the mineralogy, texture, and structure of the local terrain. The original designs of the Pancam were created at Ball Aerospace in Boulder, so there is a local connection to the MER mission.
Miniature Thermal Emission Spectrometer (“Mini-TES”): for identifying promising rocks and soils for closer examination and for determining the processes that formed Martian rocks. The instrument was also designed to look skyward to provide temperature profiles of the Martian atmosphere.
Mössbauer Spectrometer (“MB”): for close-up investigations of the mineralogy of iron-bearing rocks and soils.
Alpha Particle X-Ray Spectrometer (“APXS”): for close-up analysis of the abundances of elements that make up rocks and soils.
Magnets: for collecting magnetic dust particles. The Mössbauer Spectrometer and the Alpha Particle X-ray Spectrometer are designed to analyze the particles collected and help determine the ratio of magnetic particles to non-magnetic particles. They can also analyze the composition of magnetic minerals in airborne dust and rocks that have been ground by the Rock Abrasion Tool.
Microscopic Imager (“MI”): for obtaining close-up, high-resolution images of rocks and soils. This provided the equivalent of a geologist’s hand lens.
Rock Abrasion Tool (RAT): for removing dusty and weathered rock surfaces and exposing fresh material for examination by instruments onboard. This provided the equivalent of a geologist’s rock hammer.
Unfortunately for Spirit, the interpretation of the geologic history at Gusev Crater was incorrect—at least as far as what rocks were exposed on the surface at the landing site. It turned out that the floor of Gusev as far as Spirit’s Pancam could see is covered with rocks that are volcanic in origin, either lava flows or ash deposits. An arduous two-month traverse was conducted to a 250 m (820 ft) diameter crater named “Bonneville,” where it was hoped a window through the volcanic rocks would be provided. This proved futile, however, as the rim of Bonneville contained only severely impact-brecciated volcanic rocks.
Approximately 2.7 km (1.7 mi) to the southeast, Spirit’s Pancam detected a group of hills on the horizon. It was decided to make a dash for these hills, (named the “Columbia Hills” after the fallen space shuttle Columbia), in the hope the hills may consist of some older rocks that were not all volcanic. It was not known how long it would take to drive Spirit to the Columbia Hills, as some days only 30 m (100 ft) of progress could be made because of all of the surface obstacles that had to be circumnavigated. There was also a great deal of concern for how much longer Spirit could continue operating. Spirit arrived at the Columbia Hills 59 days after starting the dash, averaging better than 70 m (230 ft) a day.
Spirit explored the Columbia Hills until becoming entrapped there last March. Among significant Columbia Hills findings were hydrated sulfate minerals and high silica soils that indicate past hydrothermal activity. Thus, Spirit identified the presence of two critical ingredients necessary for life on Mars: liquid water and heat. Spirit also found carbonate minerals that suggest a warmer and wetter Martian environment in the past.
Opportunity continues active exploration of Mars and has driven more than 30 km (18.6 mi) as of June 2, 2011. Unlike Spirit’s misfortune, Opportunity landed within Pancam image range of a ridge that could be considered a geologist’s treasure trove of sedimentary features. Investigations of the Meridiani Planum hematite layer identified the source to be hematite-rich concretions about the size and shape of blueberries that had weathered out of layered sediments. Opportunity has conducted traverses down the bedded flanks of Endurance Crater, taking multiple sample measurements that were used to construct the first stratigraphic section on another planet. Opportunity photographed ripple trough-cross-laminations using the Microscopic Imager tool that sedimentologists who interpreted the images agreed were evidence for flowing water.
As we bid a fond farewell to the Spirit rover, it is important to remember that it is not just how long the rover lasted, but how much geologic exploration and discovery Spirit has contributed to our understanding of Mar’s history. A job well done—actually extremely well done by Spirit and all of those involved with the NASA JPL MER program!
Selected References and Websites:
Bell, J.F., 2006, Postcards from Mars: Dutton/ Penguin, New York. 196 pp. Contains an excellent collection of Pancam images compiled by the lead scientist for the Spirit and Opportunity Pancam color cameras.
Cabrol, N.A., et al., 2003, Exploring Gusev Crater with Spirit: Review of science objectives and testable hypotheses, J. Geophys. Res., 108(E12), 8076, doi:10.1029/2002JE002026.
Christensen, P.R., S.W. Ruff, R.L. Fergason, T.D. Glotch, N. Gorelick, B.M. Jakosky, M.D. Lane, A.S. McEwen, H.Y. McSween, Jr., G.L. Mehall, K. Milam, J.E. Moersch, S.M. Pelkey, A.D. Rogers, and W.B. Wyatt, Mars Exploration Rover candidate landing sites as viewed by THEMIS, Icarus, 187, 12-43, 2005.
Squyres, S., 2005, Roving Mars: Spirit, Opportunity and the exploration of the Red Planet: Hyperion, New York, 422 pp. Excellent description of the rovers from their earliest designs through their first nine months on Mars written by the rover team’s Principal Investigator. Highly recommended.
NASA JPL Mars Exploration Rover website: http://marsrovers.jpl.nasa.gov/home/index.html.
Website that contains May 24th and 25th, 2011 Spirit rover press releases: http://marsprogram.jpl.nasa.gov/news/whatsnew/.
Website that contains many MER Pancam images: http://pancam.astro.cornell.edu/pancam_instrument/images.html.
Website that contains much of the scientific data gathered by the MER rovers: http://an.rsl.wustl.edu/mer/merbrowser/default.aspx?m=MERA.
Website where a video of the April 6, 2005 U.C. Berkeley lecture by Steve Squyres, the MER Team’s Principal Investigator is available for viewing: http://video.google.com/videoplay?docid=6464250196801743722#. [link not active]
Website where NASA’s terrestrial planetary data are archived: http://pds-geosciences.wustl.edu.