The rover solar array is seen to be accumulating dust at a rate of about a quarter of a percent of coverage per day. This is very close to the coverage of 0.22% predicted [G. Landis, "Dust Obscuration of Solar Arrays," Acta Astronautica, Vol. 38, No. 11, pp. 895-891 (1996)]. The deposition rate seems to be the same on the sols when the rover is in motion as it is on sols when the rover remains in place, indicating that the deposition is probably due to dust settling out of the atmosphere, not dust kicked up by Sojourner's motion.
The dust deposition apparatus is shown in the figure. Information on the experiment can be found at the Lewis web site. The MAE solar cell experiment was built by Geoffrey Landis of the Ohio Aerospace Institute and Phillip Jenkins of Essential Research, Inc.