A condensed chart showing the operational timelines of both Mars Exploration Rovers. Black lines and ticks denote Earth years and months. Gray bars represent the winter season in Mars' southern hemisphere. Pale blue bars denote Earth-Mars solar conjunction, when communication is difficult. Dark red bars denote the 90-sol prime missions. Bright red bar denotes the serious sandstorm that darkened Mars' sky and impacted the function of instruments on both rovers.