National Aeronautics and Space Administration scientists said Mars will be at the closest point to the sun in the planet's 23-month, elliptical orbit Tuesday. One month later, Mars' equinox will mark the start of summer in the planet's southern hemisphere. That atmospheric-warming combination, NASA said, makes the coming weeks the most likely time of the Martian year for the development of dust storms severe enough to affect the rovers' activities.
"Since the rovers are solar-powered, the dust in the atmosphere is extremely important to us," said Bill Nelson of NASA's Jet Propulsion Laboratory and chief of the engineering team for Spirit and Opportunity.
Researchers said global dust events don't occur every Martian year, but if they do occur it is at this time of year.