Solar Arrays
Two solar arrays, each 3.53 meters (11.6 feet) long by 1.85 meters (6.1 feet) wide gather power from the Sun to generate electricity. Each array mounts to the main body of the spacecraft close to the attachment point between the equipment and propulsion modules. Rectangular-shaped, metal flaps attached at the ends of both arrays add another 81.3 centimeters (32 inches) to the overall structure. These "drag flaps" serve no purpose other than to increase the spacecraft's susceptibility to air resistance when it flies through the Martian atmosphere to lower its orbit.
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(From NASA)