Reprinted from the February 2004 edition of the Mössbauer Spectroscopy Newsletter, published as part of Volume 27, Issue 2 of the Mössbauer Effect Reference and Data Journal

2004 has been quite a year so far, as the international Mössbauer community watches and celebrates as two Mössbauer spectrometers operate on the surface of Mars. The two spectrometers are, of course, aboard the NASA Mars Exploration Rovers “Spirit” and “Opportunity”, which landed on Mars January 4 and January 25, respectively. The MIMOS II (from MIniaturized MOssbauer Spectrometer) backscattering Mössbauer spectrometers on board the Mars Exploration Rovers were developed for space exploration by the Mars Mössbauer Group at Universität Mainz, headed by Dr. Göstar Klingelhöfer.

The first-ever Mössbauer spectrum recorded on the surface of another planet was received from the MIMOS II spectrometer aboard Spirit on January 17, 2004. That spectrum is featured on our front cover. Since then, both Spirit and Opportunity have repeatedly used their Mössbauer spectrometers to examine the surface of Mars and the Rovers have sent that data back to Earth. Initial results suggest that water-driven processes exist on Mars. The following is a series of photos and spectra compiled from data sent to Earth from the two Mars Exploration Rovers. The graphics and caption text following each image are courtesy NASA/JPL-Caltech, and can be found on the JPL Web site at http://photojournal.jpl.nasa.gov.

The above graph or spectrum captured by the Mössbauer spectrometer onboard the Mars Exploration Rover Spirit shows the presence of three different iron-bearing minerals in the soil at the rover’s landing site. One of these minerals has been identified as olivine, a shiny green rock commonly found in lava on Earth. The other two have yet to be pinned down. Scientists were puzzled by the discovery of olivine because it implies the soil consists at least partially of ground up rocks that have not been weathered or chemically altered. The black line in this graph represents the original data; the three colored regions denote individual minerals and add up to equal the black line.

The Mössbauer spectrometer uses two pieces of radioactive cobalt-57, each about the size of pencil erasers, to determine with a high degree of accuracy the composition and abundance of iron-bearing minerals in martian rocks and soil. It is located on the rover’s instrument deployment device, or “arm.” Image Credit: NASA/JPL/University of Mainz

Image Credit: NASA/JPL/University of Mainz

The above spectrum - the first taken of a rock on another planet - reveals the different iron-containing minerals that makeup the martian rock dubbed Adirondack. It shows that Adirondack is a type of volcanic rock known as basalt. Specifically, the rock is what is called olivine basalt because in addition to magnetite and pyroxene, two key ingredients of basalt, it contains a mineral called olivine. This data was acquired by Spirit’s Mössbauer spectrometer before the rover developed communication problems with Earth on the 18th martian day, or sol, of its mission.

The above image taken at Meridiani Planum, Mars, by the panoramic camera on the Mars Exploration Rover Opportunity shows the rover’s Mössbauer spectrometer (circular device in center), located on its instrument deployment device. The image was acquired on the ninth martian day, or sol, of the rover’s mission.

The above spectrum of the soil at Opportunity’s landing site, Meridiani Planum, shows the presence of the shiny green mineral called olivine also seen at Spirit’s landing site, Gusev Crater. Based on this data, scientists believe the soil at Meridiani is made up, in part, of finely grained basalt, a type of volcanic rock. The spectrum was captured by Opportunity’s Mössbauer spectrometer.

The above close-up image of Spirit’s instrument deployment device, or “arm,” shows the donut-shaped plate on the Mössbauer spectrometer. This image makes it easy to recognize the imprint left by the instrument in the martian soil at a location called “Peak” on sol 43 (February 16, 2004). This image was taken by the rover’s panoramic camera on sol 39 (February 11, 2004).

The above elevation map of a soil target called “Peak” was created from images taken by the microscopic imager located on Spirit’s instrument deployment device. The image reveals the various high and low points of this spot of soil after the Mössbauer spectrometer was gently placed down on it. The blue areas are farthest away from the instrument; the red areas are closest. The variation in distance between blue and red areas is only 2 millimeters, or .08 of an inch. The images were acquired on sol 39 (February 11, 2004).

The above image, taken by the microscopic imager on Spirit, reveals an imprint left by the Mössbauer spectrometer. The imprint is at a location within the rover wheel track named “Middle of Road.”

Not only was the Mössbauer spectrometer able to gain important mineralogical information about this site, it also aided in the placement of the microscopic imager. On hard rocks, the microscopic imager uses its tiny metal sensor to determine proper placement for best possible focus. However, on the soft martian soil this guide would sink, prohibiting proper placement of the microscopic imager. After the Mössbauer spectrometer’s much larger, donut-shaped plate touches the surface, Spirit can correctly calculate where to position the microscopic imager.

Scientists find this image particularly interesting because of the compacted nature of the soil that was underneath the Mössbauer spectrometer plate. Also of interest are the embedded, round grains and the fractured appearance of the material disturbed within the hole. The material appears to be slightly cohesive. The field of view in this image, taken on Sol 43 (February 16, 2004), measures approximately 3 centimeters (1.2 inches) across.

The above image was taken by the microscopic imager on Opportunity’s instrument deployment device. The image shows the imprint of the donut-shaped plate on the rover’s Mössbauer spectrometer. The Mössbauer spectrometer was deployed within the trench to investigate the fine-grained soil for iron-bearing minerals. The area in this image measures approximately 3 centimeters (1.2 inches) across.

The above spectra, taken by Opportunity’s Mössbauer spectrometer, shows the presence of an iron-bearing mineral called jarosite in the collection of rocks dubbed “El Capitan.” “El Capitan” is located within the outcrop that lines the inner edge of the small crater where Opportunity landed. The pair of yellow peaks specifically indicates a jarosite phase, which contains water in the form of hydroxyl as a part of its structure. These data suggest water-driven processes exist on Mars. Three other phases are also identified in this spectrum: a magnetic phase (blue), attributed to an iron-oxide mineral; a silicate phase (green), indicative of minerals containing double-ionized iron (Fe2+); and a third phase (red) of minerals with triple-ionized iron (Fe3+).

JPL is a division of the California Institute of Technology, Pasadena. It built the rovers and manages the Mars Exploration Rover project for the NASA Office of Space Science, Washington, D.C. Information about the rovers and the scientific instruments they carry is available online from JPL at:

http://marsrovers.jpl.nasa.gov/home/index.html

and from Cornell University, Ithaca, N.Y., at:

http://athena.cornell.edu

The Web site for the Mars Mössbauer Group at Universität Mainz can be found at:

http://iacgu7.chemie.uni-mainz.de/klingelhoefer/mer.html

Raw and processed Mössbauer data from Mars are being posted to the following Web sites:

http://www.ak-klingelhoefer.chemie.uni-mainz.de/

http://www.mtholyoke.edu/courses/mdyar/database/index.shtml?group=mera

http://www.mtholyoke.edu/courses/mdyar/database/index.shtml?group=merb