9781422283721

Int roduct ion

T

his book looks at the three plan- ets that are nearest the Earth in the Solar System , Mercury, Venus, and

Mars. Mercury and Venus both lie closer to the Sun than the Earth, while Mars lies further away. All three planets are made up mainly of rock like the Earth, and astronomers call them the terrestrial , or Earth-like planets. But these planets are unlike the Earth in most other ways. Mercury is a searing hot world, baked by the nearby Sun. Venus gets equally hot because its heavy atmosphere traps the Sun’s heat like a gigantic greenhouse.