Opportunity took this photo of its robotic arm using the navigation camera mounted on the mast.
The Rover's 'vital organs', which include motors and electronics, must be kept at operating temperatures between +40 and -40 degrees C. Chemical reactions within the batteries need a optimal temperature of +20 degrees C. All these components are kept safe within the Rover's 'body', which is well insulated to prevent heat loss, and warmed by electrical heaters.
The Rover has a built-in safety switch that will disable a heater to prevent overheating of individual components.
The Mars Exploration Rover, Opportunity, developed a problem with a heating switch on the 'shoulder' joint of the Robotic Arm, which meant the heater was turned off at night. The joint became extremely hot during the day and extremely cold at night. Such huge temperature swings make electric motors wear out faster, and eventually Opportunity's robotic arm could not be stowed away for driving. The engineers had to devise a strategy for driving the rover safely with the arm deployed.
Learn more about the role of the Thermal Engineer in Mission Control.