Simulating Collection of Dust on the RAT Magnets Onboard the Mars Exploration Rovers

Introduction: Rock Abrasion Tool (RAT) [1, 2] are a part of the Instrument Deployment Device (IDD) in­ strumentation on the Mars Exploration Rovers (MERs), Spirit and Opportunity. The RAT can brush and grind selected rocks on the martian surface and thereby remove dust and the outer, weathered rind of the rocks. The grinding tool can remove up to about 5 mm of a rock and the grinding process produces dust, which may for a while be locally suspended in the at­ mosphere. In this study we have grinded the two Brazilian hematite-rich rocks with a RAT simulator in order to learn more about the dust collected by RAT magnets. By Mossbauer measurements it is possible to compare the dust collected by the magnets with the bulk compo­ sition of the rock being investigated. The RAT magnets: There are four magnets inte­ grated into the RAT housing and these magnets sponta­ neously attract some of the magnetic particles that are liberated by the grinding process. The main purpose of the RAT magnet experiment is to provide information about magnetic material in the rocks and thereby give information about the rock composition that will be supplementary to information gathered by the APXand the Mossbauer spectrome­ ters of the IDD. There are three different RAT magnets; two of the four magnets (#1) are identical and very strong. These mag­ nets are designed to attract all magnetic particles from the grinding process that happen to come close to these magnets. The two other RAT magnets (#2 and #3) are different. They are less strong and are designed so they have a lower ability to attract and hold magnetic mate­ rial. This leads to a preferential attraction of only the more strongly magnetic particles that are liberated dur­ ing the grinding process. Less magnetic particles will be loosely bound on these weaker magnets and easier fall off if the RAT is moved – or if other particles ar­ rive at the surface of that particular magnet. Essentially we have seen reddish rock dust on the Op­ portunity landing site and more dark or grayish dust collected on Spirits RAT magnets. Examples are shown in fig. 2. Fig 1: Location of the magnets on the bottom of the RAT. The two identical strong magnets are labeled #1, the less strong magnets (of different strength) are la­ beled #2 and #3, respectively. Brush and grinding wheel are removed for clarity.