Try your hand at these exercises on commas and semicolons based on recent articles on the Pathfinder mission to Mars by Sharon Begley, "The Stars of Mars," Newsweek 21 July 1997: 27-29+, and by Richard Turner, "Who Needs Astronauts," Newsweek 21 July 1997: 33. 

• Click on words after which a comma should appear in the following sentences or on words after which a comma has been incorrectly placed (for the purposes of this exercise).  You will receive messages according to whether your answers are right or wrong.

1. As the Martian rover paid courtesy calls up and down Ares Vallis last week she showed the exemplary manners of any ambassador.
   
   
2. Tipping a bit as she went over a rock she recovered gracefully backed up about 12 inches and stuck her spectrometer onto another rock.  (This one is a challenge!  More than one comma is needed.)
   
   
3. She was given commands by controllers in Pasadena, California and then set off on her next visit.
   
   
4. There is for instance only one radio receiver on the Pathfinder lander.
   
   
5. If it fails the rover cannot execute commands sent from mission headquarters.
   
   
6. Viking which touched down on Mars in 1976 underwent tests to see whether its parachutes worked.
   
   
7. Another cost-saving move, is to buy more parts off the shelf.
   
   
8. Goldin said "We can tolerate failures."
   
   
9. "We want to encourage people to take risks in spacecraft design" he added.
   
   
10. Philip Christensen had to design build and deliver the infrared camera used on Pathfinder.
    
    
11. Scientists knew that Ares Vallis had once been swept by a flood but Pathfinder did find some surprises.
    
    
12. She analyzed one prominent rock and she found that it contained quartz.
    
    
13. Even as the headlines ebb, people are still talking about the mission and their interest has a certain purity about it.
    
    
14. The atmospheric conditions for this story, should have been as inhospitable as those of Mars.
    
    
15. There are no signs of life no people no heroic astronauts.
    
    
16. The scientists, are the real heroes.
    
    
17. Even if we didn't quite get what they were so excited about their excitement pulled us into the story.
    
    
18. The cartoon-character stuff got a bit annoying but it served a public-relations purpose.
    
    

• Click on the words in the following sentences after which a semicolon should appear or on words after which a semicolon has been incorrectly placed (for the purposes of this exercise).

1. Our children weren't always riveted by this story the scientists themselves were the children.
   
   
2. The sometimes comic names for Martian rocks were not intended to "sell" the story they were just invented because the scientists have a sense of humor.
   
   
3. The media showed little of the usual cynicism in covering the story, however, not everything was spontaneous.
   
   
4. A future Mars lander could make oxygen out of the planet's atmosphere therefore, it would supply astronauts with breathable gas.
   
   
5. Pathfinder is changing the face of exploration in space; and it has already changed our view of Mars.
   
   
6. NASA unexpectedly ordered the use of better quality equipment; but the price of the mission was not seriously affected.