motion it was describing. Rob felt shudders rock the space ship as great powers locked in combat.

Some minutes later, Lieutenant Stone checked the dials and said with a deep sigh of relief, “I think we’ve done it! Thanks, Rob!”

They had done it. The balance was swung in favor of the Rigel as Saturn’s tiny companion continued to move away, giving up the fight. From now on the planet would appear to diminish in size, but it would be many hours before its commanding sphere would be lost among the other millions of lights in the heavens.

For days and days, nothing seemed to change in the endless depths of black space as the Rigel sped toward Pluto. There were the same monotonous patterns of stardust and the eternally broad sweep of the Milky Way and other remote galaxies. Only the distant planets grew and shrank in size. As the space ship neared Neptune, the big green world enlarged importantly. Rob and Duff, in an off-duty hour, watched the frigid, lonely planet.

“Neptune reminds me a little of Earth,” Rob said.

Duff’s brows raised questioningly. “I can’t see any similarity. Why, Neptune is four times Earth’s diameter!”

“But Neptune’s mean surface gravity is the same as Earth’s because of its low density,” Rob replied. “Like Saturn, another big puffball, Neptune has a small rocky core surrounded by huge layers of ice and atmosphere. Both Neptune and Earth have a greenish cast, and each has a satellite of about the same size and at about the same distance away.”

“There’s one big difference, though, Rob,” Duff said. “Neptune’s a zillion times colder.”

“It’s still not as cold as we’re going to find Pluto,” Rob reminded him, “near absolute zero!”

The redhead made a wry face. “Why did you have to say that? It’s so warm and comfortable in here!”

As the Rigel drove onward, thousands of miles a minute, day upon day, Rob grew impatient to reach Pluto. He was thinking of Jim Hawley and the Capella crew undergoing unknown hardship and peril. The radio circuit with the ill-fated space ship had been left open in case she was able to get a message through. But none had come during all this time, and Rob was beginning to doubt that he would ever see his fun-loving friend again.

The day finally came when the Rigel hovered over the little planet, which was not quite as large 

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