[1] The Rock Abrasion Tool (RAT) magnet experiment on the Mars Exploration Rovers was designed to collect dust from rocks ground by the RAT of the two rovers on the surface of Mars. The dust collected on the magnets is now a mixture of dust from many grindings. Here the new data from the experiment are presented. The findings from Mars are furthermore compared to simulation experiments performed on Earth. New experiments with analog rocks that mainly contain hematite indicate the likely presence of a stronger magnetic phase besides hematite in the outcrop rock formations found on Meridiani Planum, a phase which was hitherto not detected by other measurements (such as Mossbauer) on these rocks.

W. B. Brinckerhoff 1 , K. Zacny 2 , I. L. ten Kate 1,3 , A. Kusack 2 , P. G. Conrad 4 , H. B. Franz 1,5 , J. Eigenbrode 1 , P. R. Mahaffy 1 , C. M. Corrigan 6 , and T. C. Onstott 7 , 1 NASA/GSFC Code 699, 8800 Greenbelt Rd., Greenbelt, MD 20771 (william.b.brinckerhoff@nasa.gov), 2 Honeybee Robotics Spacecraft Mechanisms Corp., 460 W. 34th Street, New York, NY 10001 (zacny@honeybeerobotics.com), 3 Goddard Earth Science and Technology Center, University of Maryland, Baltimore County, MD 21228, 4 Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA (conrad@jpl.nasa.gov), 5 Dept. of Geology, University of Maryland, College Park, MD 20742, 6 Dept. of Mineral Sciences, Smithsonian Institution, PO Box 37012, MRC 119, Washington, DC 20013, 7 Department of Geosciences, B79 Guyot Hall, Princeton University, Princeton, NJ 08544.

The Rock Abrasion Tool (RAT) on board the Mars Exploration Rovers (MER) is a grinding tool designed to remove dust coatings and/or weathering rinds from rocks and expose fresh rock material. Four magnets of different strengths that are built into the structure of the RAT have been attracting substantial amounts of magnetic material during RAT activities from rocks throughout both rover missions. The RAT magnet experiment as performed on Spirit demonstrates the presence of a strongly ferrimagnetic phase in Gusev crater rocks, which based on Mössbauer and visible/near‐infrared reflectance spectra is interpreted as magnetite. The amount of abraded rock material adhering to the magnets varied strongly during the mission and is correlated in a consistent way to the amount of magnetite inferred from Mössbauer spectra for the corresponding rock. The RAT magnet experiment as performed on Opportunity also indicates the presence of a strongly ferrimagnetic phase in outcrops, such as magnetite or an altered version of magnetite. However, the evidence is weaker than in the case of Spirit. According to data from the α particle X‐ray spectrometer (APXS) and the Mössbauer spectrometer (MB), the Eagle crater outcrops should not contain magnetite and their magnetization should not exceed 0.03 A m2 kg−1. However, this assertion seems to be in contradiction with the results of the RAT magnet experiment. The evidence for a strongly ferrimagnetic phase at low abundance in the Meridiani outcrops is discussed.

The primary purpose of the Mars 2007 Phoenix Lander Robotic Arm (RA) and associated Icy Soil Acquisition Device (ISAD) is to acquire samples of Martian dry and icy soil (DIS) by digging, scraping, and rasping, and delivering them to the Thermal Evolved Gas Analyzer and the Microscopy, Electrochemistry, and Conductivity Analyzer. The RA will also position (1) the Thermal and Electrical Conductivity Probe (TECP) in the DIS; (2) the TECP at various heights above the surface for relative humidity measurements, and (3) the Robotic Arm Camera to take images of the surface, trench, DIS samples within the ISAD scoop, magnetic targets, and other objects of scientific interest within its workspace. The RA/ISAD will also be used to generate DIS piles for monitoring; conduct DIS scraping, penetration, rasping, and chopping experiments; perform compaction tests; and conduct trench cave‐in experiments. Data from the soil mechanics experiments will yield information on Martian DIS properties such as angle of repose, cohesion, bearing strength, and grain size distribution.

The Mars Exploration Rover Spirit has identified five distinct rock types in the Columbia Hills of Gusev crater. Clovis Class rock is a poorly sorted clastic rock that has undergone substantial aqueous alteration. We interpret it to be aqueously altered ejecta deposits formed by impacts into basaltic materials. Wishstone Class rock is also a poorly sorted clastic rock that has a distinctive chemical composition that is high in Ti and P and low in Cr. Wishstone Class rock may be pyroclastic or impact in origin. Peace Class rock is a sedimentary material composed of ultramafic sand grains cemented by significant quantities of Mg‐ and Ca‐sulfates. Peace Class rock may have formed when water briefly saturated the ultramafic sands and evaporated to allow precipitation of the sulfates. Watchtower Class rocks are similar chemically to Wishstone Class rocks and have undergone widely varying degrees of near‐isochemical aqueous alteration. They may also be ejecta deposits, formed by impacts into Wishstone‐rich materials and altered by small amounts of water. Backstay Class rocks are basalt/trachybasalt lavas that were emplaced in the Columbia Hills after the other rock classes were, either as impact ejecta or by localized volcanic activity. The geologic record preserved in the rocks of the Columbia Hills reveals a period very early in Martian history in which volcanic materials were widespread, impact was a dominant process, and water was commonly present.

On its traverse to Columbia Hills, the Mars Exploration Rover Spirit investigated an outcrop designated “Wooly Patch” that exhibited morphological, mineralogical, and geochemical characteristics at the extreme ends of ranges observed among rocks studied at West Spur, a westward projecting salient near the foot of the Columbia Hills, Gusev crater. The major‐element composition and Fe‐mineralogy, as determined by the Alpha‐Particle X‐ray Spectrometer and Mössbauer Spectrometer, are inconsistent with any reasonable assemblage of basaltic minerals in that there is an excess of Si and Al. The combined data are best explained by the presence of 14–17% phyllosilicate minerals. Phyllosilicates that account for the composition and cation ratios include members of the kaolinite, serpentine, chlorite, and septechlorite groups. The potential existence of kaolinite‐type Al‐rich phyllosilicates within the Wooly Patch outcrop suggests a mildly acidic environment (pH 4–6) in the past and an open hydrologic system with good drainage conditions in the environment where these rocks were altered.