A periodic examination of these particles and their patterns of accumulation on magnets of varying strength can reveal clues about their mineralogy and the planet�s geologic history. Magnets on the Mars rovers are for collecting such magnetic dust particles.

The Danish Mars Project at the �rsted Laboratory focuses on the magnetic properties of the surface dust and soil on Mars. Martian dust includes magnetic, composite particles, with a mean size of one micron - the equivalent to powdered cement or flour in consistency. This size range is about five percent the width of a human hair.

While there is plenty of dust on the surface of Mars, it is difficult to confirm where it came from, and when it was last airborne. Because scientists are interested in learning about the properties of the dust in the atmosphere, they devised this dust-collection experiment.

Each rover has three sets of magnetic targets that will collect airborne dust for analysis by the science instruments. One set of magnets will be carried by the Rock Abrasion Tool. As it grinds into Martian rocks, scientists will have the opportunity to study the properties of dust from these outer rock surfaces.

A second set of two magnets is mounted on the front of the rover at an angle so that non-magnetic particles will tend to fall off. The capture magnet has a stronger charge than its sidekick, the filter magnet.

The lower-powered filter magnet captures only the most magnetic airborne dust with the strongest charges, while the capture magnet picks up all magnetic airborne dust.

The capture magnet is about 4.5 centimeters (1.8 inches) in diameter and is constructed with a central cylinder and three rings, each with alternating orientations of magnetization. Scientists have been monitoring the continual accumulation of dust since the beginning of the mission with panoramic camera and microscopic imager images.

These magnets will be reachable for analysis by the M�ssbauer and APXS instruments. A third magnet is mounted on the top of the rover deck in view of the Pancam. This magnet is strong enough to deflect the paths of wind-carried, magnetic dust.

The M�ssbauer Spectrometer and the Alpha Particle X-ray Spectrometer then analyze the particles collected and help determine the ratio of magnetic particles to non-magnetic particles. They also analyze the composition of magnetic minerals in airborne dust and rocks that have been ground by the Rock Abrasion Tool.

Actual mini-tornadoes of this magnetic dust, or dust devils, have been caught in the act by orbital cameras are highlighted by images below. These miniature tornadoes can span about 10 to 100 meters wide with 20- to 60-mile-per-hour (32- to 96-km/hr) winds swirling around a heated column of rising air.

One might expect to see several dust devils per hour from an active site on Mars between 10 am and 3 pm, when rising afternoon air is hottest.

In his first press conference after the Spirit rover landed, the principal investigator for the rover's science package, Cornell's Steven Squyres, described one instance his team has been discussing: the intriguing possibility that at Gusev, over their mission, the rover's camera may actually be able to animate a dust devil in action.

That fortuitous afternoon timing of an unpredictable atmospheric event has so far proven elusive to animate.

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