“I don’t think catchers would be a very good game to play on these moons,” chuckled Professor Palmer. “You see, a person wouldn’t weigh much more than a feather on one of them, and if he took a real good leap on the under side he might find himself on his way to Mars. Not only that; there is no atmosphere on them, and you could not exist an instant in the vacuum and intense cold prevailing there, even if you were equipped with respiration tanks.” “That’s enough for me,” Taggert decided with a grimace. “How cold do you think it is out in space like that?” asked Robert. “Absolute zero--the nadir of temperature--is said to be 459 degrees below zero Fahrenheit.” “Enough, enough,” shouted Taggert. “I said I was satisfied without getting out on a moon.” “There’s Deimos over there now,” cried the professor suddenly, pointing. “Don’t know the lady,” commented the reporter. Nevertheless he looked interestedly, and a trifle uneasily in the direction indicated. “Deimos, or ‘Fear,’ is the moon farthest from Mars; Phobus, meaning ‘Panic,’ is the other,” the professor explained. Off toward the northwest, just beyond the outer rim of the planet, a small star was suspended. It appeared much like any ordinary star in spite of its small bulk, for it was much closer than the vastly larger stars which we are accustomed to see. “Now we must keep clear of that one, and watch closely for the other,” cautioned Professor Palmer. At an elevation of about 3,000 miles nothing of the other moon had been seen, and it was concluded that it was then on the opposite side of the planet. But they were soon to find out their mistake--one that nearly proved fatal. It happened while all three were intent upon the nearing planet, which presented a sight of such interest that even Professor Palmer had temporarily forgotten his own recent warning. Their sole warning was a sudden cessation of the sun’s rays. Darkness reigned, except for the reflection from the Martian disk below. The abruptness of it made them gasp in unreasoning terror. Above and around them the blackness of space was unbroken. The sun seemed simply to have gone out completely. Only the vivid sight of Mars reassured them. “The moon!” yelled Taggert, first to think of it. Hard on the heels of the realization of what had caused the sudden darkness came to Robert and Professor Palmer the knowledge that the satellite must be dangerously close to them. Otherwise, its small diameter would not have so completely hidden the sun from them. Passing between them and the sun, there was no longer danger of its crashing into them, but it was not entirely improbable that it might attract the _Sphere_ toward it, with disastrous results.