Full-scale mock-up of the Phobos 

 spacecraft displayed at ttie 1987 

 Paris Air Show, counesysovioio 



Beyond the orbit of Mars lie several belts of orbiting 

 asteroids, and they separate what is called the Inner 

 Solar System from the Outer Solar System. The Inner 

 Solar System contains the solid rock planets, Mercury, 

 Venus, Earth, and Mars. The asteroids themselves are 

 solid rock planets, but are very small; the largest is only 

 300 miles in diameter, and they range downward to 



gravel-size bits and pieces. There are thousands of 

 them. But, beyond them, the Solar System takes on a 

 very different aspect. The planets of the Outer Solar 

 System are giants — Jupiter, Saturn, Uranus, and Nep- 

 tune. Only little Pluto, with its weird orbit, may be a 

 solid rock body like the inner planets. Jupiter, Saturn, 

 Uranus, and Neptune, are enormous balls of gases, roil- 



Phobos Spacecraft 

 Orbits Around Mars 



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