Air-fall dust accumulates on the solar panels of NASA's Mars Exploration
Rovers, reducing the amount of sunlight reaching the solar arrays.
Pre-launch models predicted steady dust accumulation. However, the rovers
have been blessed with occasional wind events that clear significant
amounts of dust from the solar panels.
This graph shows the effects of those panel-cleaning events on the amount
of electricity generated by Spirit's solar panels. The horizontal scale is
the number of Martian days (sols) after Spirit's Jan. 4, 2005, (Universal
Time) landing on Mars. The vertical scale indicates output from the
rover's solar panels as a fraction of the amount produced when the clean
panels first opened. Note that the gradual declines are interrupted by
occasional sharp increases, such as a dust-cleaning event on sol 420.
