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Lyle Gertsch, age 12, of Hebet Utah for his question:

Are all the moons in the universe the same?

A moon must belong to a planet and the only planets we know are in our Solar System. Thus, the only moons we know are also in our own Solar System Of course, among billions of stars, there are almost certainly, other Solar Systems. But our telescopes are not able to detect which starry suns have families of planets.

Our nine planets are different from each other in size and weight. And there is no law which says how many moons each one of them should have. A planet may have no moons, one moon or any number up to a dozen moons and, so far as we know, each moon in the Solar System is different from all the rest.

The two inner planets, little Mercury and golden Venus, have no moons at all. Next comes the earth with a solitary moon. Ours is a fair‑sized moon, with a diameter over one fourth that of its parent planet.

Mars has two very, very small moons, which astronomers have named Phobos and Deimos. These little satellites are maybe no more than 10 or 20 miles in diameter at most.

Next comes giant Jupiter, with a whole family of moons. The four largest can be seen through a pair of field Masses. These big satellites compare in size with the earth s solitary moon. They were first seen in 1610 when Galilee turned his small telescope on the heavens.

Jupiter's inner moon, Jupiter, is very small and was not discovered until 1892. The next one is 102,450 miles in diameter. Then comes a slightly smaller moon called Europa. The fourth and fifth moons are the biggest satellites of the Solar System. They are Ganymede, 3,560 miles in diameter, and Callisto, 3,350 miles in diameter. The rest of Jupiter's dozen moons are too small to be given names or exact measurements. Each is named Jupiter, followed by a number.

Beyond Jupiter is Saturn, with its golden rings plus a family of nine moons. The smallest and the most remote of them is Phoebe, with a diameter of about 200 miles. A11 of Saturn's satellites arc large enough to have names and one is the most remarkable moon in the whole Solar System.

The two smallish inner moons are Mimas and Enceladus. Then comes Tethys, Dione and Rhea, each well over 1,000 miles wide. Then comes remarkable Titan, 3,000 milers wide and having an atmosphere of its own. Its gases, like those of its parent planet seem to be mostly methane and ammonia. But Titan is the only moon known to have a blanket of air.

Uranus is so far away that it can barely be seen without a telescope. Yet the astronomers have found that it has four moons, ranging from 400 to 1000 miles in width. Neptune, too far away for our eyes to see, is known to have at least one satellite estimated to be about the size of our moan.

Each moon in the Solar System differs in size and weight from all the rest. They range from under ten to over 3,000 miles in width. Each follows its own special orbit around its parent planet. And, seen from its planet, each looks different from all the rest.

For latest information: Go to Science News in YouAskAndy main menu, click on NASA Jet Propulsion Laboratory

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