Measuring Dust on Mars

 
Cumulative dust deposition measured by rotating a quartz cover from a solar cell on the Sojourner rover (nearest corner in the photograph). Electrical heating of a 3-cm NiTi wire decreases its length by 5% to overcome a conventional return spring. Dust accumulated linearly at 0.28% per day, having implications for solar power production.

Mars Pathfinder, July 5, 1997, http://photojournal.jpl.nasa.gov, JPL image PIA01551