Each rover will carry several magnets, which will all analyze the dust particles found on Mars. Studying dust on Mars is important because XXXXXXXXXXXXXX.

Magnet Array: Previous Mars landers (the two Vikings and Mars Pathfinder) had magnetic arrays that collected magnetic particles from the surface and from windblown dust near the surface. The Mars Exploration Rover version of the experiment includes magnets to attract airborne Martian magnetic materials from higher in the atmosphere. The robotic arm will deliver the arm-mounted spectrometers to a position where they may investigate the magnetic particle collection. (It has not yet been established whether the magnets will be visible to the Microscopic Imager and/or Pancam.)

The experiment is a significant scientific step beyond its predecessors because of the unique mineralogical capabilities of the Mössbauer spectrometer. The magnets also fill an important scientific gap left by the fact that the APXS on the Sojourner rover did not measure the composition of the dust that adhered to the magnet on the Mars Pathfinder landing ramp. The magnets array includes three elements: one filter magnet and one capture magnet mounted on the rover's magnet array; a "sweep magnet" mounted on the rover deck, and four "RAT magnets," so-called because they are mounted within the Rock Abrasion Tool, or RAT.

The filter and capture magnets are mounted on a magnet array on each rover, which is accessible to the Mössbauer spectrometer and APXS. The stronger "capture" magnet is designed to attract all iron-containing dust and magnetic-iron dust, while the weaker "filter" magnet is designed to attract only the most magnetic dust. The filter and capture magnets are each contained within an aluminum disk 45 millimeters in diameter. Each will be positioned as high as possible on the rover, in a position clear of the solar panels. The capture magnet is designed to accumulate a homogenous layer of dust as efficiently as possible, and to provide a relatively constant magnetic field at the position of the dust layer. Based on experience from the magnetic properties experiment on Mars Pathfinder, it is expected that the capture magnet will collect sufficient material for analysis by the Mössbauer spectrometer in about 15 martian days.

The filter magnet will also collect airborne dust particles dropping to the magnet from the atmosphere. It is designed to accumulate a homogenous layer of strongly magnetic dust, and to attract weakly magnetic dust as little as possible. After about 30 Martian days, the magnet should have attracted enough particles for examination by the Mössbauer spectrometer.

Sweep Magnet: An unresolved question from the Viking and Pathfinder missions is whether magnets are culling a population of more strongly magnetic particles from the airborne dust, or whether all dust particles have similar magnetic properties. The sweep magnet is designed to answer this question. This magnet consists of a thin-walled magnetic tube magnetized along its symmetry axis. With this configuration it is possible to make a strong magnet capable of deflecting the paths of wind-transported, magnetic particles arriving at the surface of the magnet. Magnetic particles will accumulate on a narrow ring corresponding to the magnetic tube. The central surface inside the ring magnet will only collect non-magnetic dust particles. At greater radial distances from the ring magnet, both magnetic and non-magnetic particles will accumulate. Pancam images of the sweep magnet will provide spectral information on the dust collected, and thus provide information on the relative amounts of magnetic versus non-magnetic particles exist in the Martian dust.

RAT Magnets: When the Rock Abrasion Tool (RAT) grinds away a rock surface, the abraded rock particles will sample and concentrate the magnetic portion of the particles for investigation by the Panoramic Camera. Pancam images can be used for characterizing the types of magnetic minerals in Martian rocks. The RAT magnets will have different strengths, providing a range of conditions for magnetic particles to be attracted and held. A set of four 7 mm diameter by 9 mm thick magnetsXXXXXX [need size comparison] will be mounted within the RAT. Once the particles have been examined, the sample platform will be cleared through a temperature-driven retraction mechanism [Need spotlight/sidebar on this ingenious device]. As temperatures drop at night, the collection area will slide into a sleeve, pushing off any particles on its surface, clearing the way for new rock samples.