Mike Sheidy, age 14, of Andrews, N. C., for his question:
Do all the planets have moons?
Giant Jupiter has 63 moons, two of them bigger than our moon and two about the size of the planet Mercury. Imagine a moonlight night on the giant planet. Actually, we would be very disappointed. Our full moon is three times brighter than all Jupiterts moons shining their brightest. And the sun shines on us 465,000 times brighter than our golden moon when it is full. Even so, though not the largest, our moon is the brightest in the Solar System.
Altogether there are 31 known moons in our Solar System. Earth is the only planet with a single moon. Other moons are larger, but we get more moonlight than any other planet, perhaps more than all the other planets combined. This is because ours is the moon nearest to the sun. Mercury and Venus, the two inner planets, are moonless. Our telescopes have not found a moon for little Pluto at the outside rim of the Solar System.
The moons of other planets have been spotted on telescopic pictures and there is no proof that all of them have been found. Any day we may hear of a newly discovered moon belonging to Saturn, Neptune or even Pluto.
The big planets have the largest families of satellites. These planets have the strongest gravity, the force which keeps a satellite orbiting around its parent planet. Some of Jupiter’s 12 children are 15 million miles from the big planet. They are too small and too far from Jupiter to shed any moonlight.
Saturn has 46 known moons, all of them outside the golden rings. Six of them are less than 1,000 miles wide. Titan, the sixth moon, is larger than our moon and is the only moon to have its own atmosphere, Uranus has five moons, all of them less than 1,000 miles wide. Neptune has two satellites, one of them closer to the planet and much larger than our moon.
The two remaining moons of the Solar System belong to Mars. They are Phobos and Deimos both of them less than ten miles wide. The orbit of Phobos is about 4„000 miles above the planet and it whizzes around its orbit three times during the Martian day. It looks perhaps like one of our man made satellites tumbling over the sky. Deimos, the smaller of the little moons of Mars, orbits 149000 miles above the planet. It is only one third as bright as its sister satellite.