Benjamin Funk, age 11, of 01d Bridge, New Jersey, for his question:

Do all Jupiter's moons have names?

The two little moons of Mars are named for the mythical dogs that attended the Roman god of war. The names of Saturn's moons also are borrowed from mythology and the moons of Uranus are named for legendary characters of fairyland. But most of Jupiter's moons have numbers instead of names.
This story begins on a rooftop in Italy. It was the night of January 7, in the year 1610, and the great Galileo was scanning the skies through his home made telescope. All winter he had been spotting heavenly objects never seen before and carefully noting down his observations. He had seen the clouded face of giant Jupiter    and tonight he saw something else. His little telescope revealed that the big, bulky planet had four moons. He reported these satellites but he did not name them.
The world of astronomers finally accepted the work of Galileo and gave him the credit he deserved. He is still recognized as the first scientist to view the heavens through a telescope and the first to discover many objects beyond the range of human vision. However, Simon Marius of Germany claimed that he also used a telescope in 1610. In fact, he later claimed that he saw the four moons of Jupiter on January 8, the night after Galileo saw them. What's more, he named them Io, Europa, Ganymede and Callisto.
Many astronomers doubted this claim of Marius and for a long time refused to use the names he had given to Jupiter's four brightest moons. Nowadays, however, some astronomers accept his story and use the four names he borrowed from ancient mythology. Later telescopes revealed eight more Jovian satellites and they were named with numbers in order of their discovery. Some astronomers still number Galileo's four moons in order of their distances from Jupiter.
Io and Europa are about the same size as our moon and less than half a million miles from the planet. Ganymede and Callisto are 50% bigger than our moon or about the size of the small planet Mercury. No other satellite in the Solar System can compare with them in size. In 1892, a little moon was found much closer to the big planet and named Jupiter V.  
Jupiter VI and Jupiter VII were discovered in 1905 and, one by one, the list has now grown to 12. The two outside satellites are Jupiter VIII and Jupiter IX. Both of them are more than 14 million miles from giant Jupiter and both take more than two earth years to complete their lunar orbits. Jupiter XII, the last to be discovered, orbits between Jupiter VII and Jupiter XI.
The four Jovian moons observed by Galileo are whoppers and if you have even a small telescope you can spot them and track their orbits. The other eight satellites of Jupiter are among the smallest known moons in the Solar System. They can be spotted only on telescopic photo plates and their sizes are hard to measure. Several of them seem to be only 10 to 15 miles wide. Jupiter V, the biggest of the eight, is estimated to have a diameter of no more than 100 miles. Various planetary spacecraft have provided new data and pictures of Jupiter  and its moon which now number 63 and a single very thin ring.
The following are statistics on Jupiter.
    Jupiter's Statistics
    Planetary Symbol: Name in Roman/Greek Mythology: Jupiter/Zeus
    Diameter: 142,800 km
    (88,736 miles) Rotation Period about Axis: 9.8 hours
    Mass: 1,898 x10^24 kilograms (318 x Earth's)
    Revolution Period about the Sun: 12 years
    Density: 1,326 kg/m^3 Tilt of Axis: 3.1o
    Minimum Distance from Sun: 741 million km (460 million miles)
    Surface Gravity: 23.12 m/s^2 (2.64 x Earth's)
    Maximum Distance from Sun: 817 million km (508 million miles)
    Distance across the Great Red Spot: 40,000 km (24,860 miles)
    Orbital Semi-major Axis: 5.20 AU (Earth=1 AU)
    Temperature at Cloud Tops: -150o C (-101o F)
    Minimum Distance from Earth: 588 million km (365 million miles)
    Average Cloud Top Temperature (K): 123K
    Rings: 1, very thin;  Satellites: 63 known