"Yes, just as Two will for those who like it hotter." Jon's eyes shone. "Pop sure picked a winner when he decided to explore this system. Even with just these two worlds he has a prize." "_If_ they accept our work as proof. Wonder what the fourth planet will be like?" Jak continued in a different tone. "Cold. Lots colder, probably, than Mars." "Then it won't do us any good?" "Depends on what's on it in the way of metals that can be mined. Maybe we'll find something there. Might be natural gems or jewels, too." "And anyway, cold never stopped man." "That's right," Jon said admiringly. "They have mines on Pluto, even--although they're mostly worked by automatics while the men stay warm in their bubble-cities." As the _Star Rover_ approached closer to the distant, smaller planet they had named "Jon," their instruments showed it to have a diameter of about 4400 miles, and a density of about 4.6, a little lighter than Terra. This meant the gravity would be a bit weaker, and they would weigh less than on their home planet. Four was almost a quarter of a billion miles from the sun, and would be very cold, as Jon had said. While their ship drove in closer, the boys' mother came into the control room. All three Carvers stared excitedly into their visiplates, watching their rapid approach to this new world. Would they find anything of value there, or was it simply a barren wasteland of ice and frozen air and rocks, far too cold and forbidding for men even to bother trying to explore it? When Jak, eyes still glued to the telescopic sights of his spectro-analyzer, voiced something of this, Jon drawled, "You know better than that, Owl. We said just yesterday that there's no place, no matter how bad, that man won't explore to see if there's anything he can possibly use. They'll follow us here, don't worry." After cruising about the surface for some time, recording their data and taking the needed pictures, they saw a fairly level valley, ice-covered and bare, and Jon set the ship down there. By now he was becoming an expert astrogator and pilot, and with his new controls they could hardly feel the jar of the ship's landing. "How's the temp outside?" Jak was examining the gauges. "About a hundred below, and not a bit of moisture, naturally. Going to try going out?" "I don't...." their mother started to speak against it, but made herself stop. Her boys were showing such resourcefulness and unexpected habits of caution that she felt she must let them decide things for themselves, even though her motherly instinct was always to hold them back from possible dangers. "Sure we're going out for a bit," Jon answered his brother, then faced their mother. "It'll be all OK, Mom," he said affectionately. "We'll wear our suits, of course, with the heaters on. We won't go far, because the moment we feel any cold we'll run back. But I want to see what it's like out there, and if there's any sort of life. We're supposed to report...."