"Nine Planets Circle the Sun."

"If it were simply a matter of chance, there'd be a lot of weight behind your argument, Ned. But a lot of other factors enter the problem. I should say that the only planets where life as we know it might exist are Mars and Venus. The latter I ruled out, for astronomers have found that it is forever covered thickly with dense clouds. Thus the inhabitants, if any, must be ignorant of any world but their own."

"What have people on the planets got to do with the question, anyhow?" asked Ned. "Huge chunks of metal break off of any heavenly body and go hurtling through space. The inhabitants don't throw them off!"

Chunks of Metal Rushing Through Space

"But our meteor was no ordinary one as we have proved already," replied Tom. "I firmly believe that someone on another planet deliberately fired that missile into space, hoping it would reach this world. Since scientists agree that Mars probably is inhabited by a highly intelligent race, that planet is a reasonable guess."

"Whew!" whistled Ned. "Such ideas are beyond me."

"Someone on Another Planet Fired the Missile."

As he finished speaking, the boys reached the Swift residence. The young inventor's father had built the handsome white house many years before his son was born. Beyond were the several buildings where the inventions of Tom Swift and his father, Barton Swift, were manufactured.