History is shaped by our hands.

There's this article about what computer components are inside the two Mars rovers that are currently doing their business on Mars. To answer the question of how the rovers stay warm at night, this was said...
To survive the frigid Martian night, MER computers are housed in warm electronics boxed heated by a combination of electric heaters, eight radioisotope heater units as well as the natural warmth from the electronics themselves.
Natural? If its coming from a man-made chip, how natural is it? Its not like there's a mini-sun in there.