S/2003 J 12 is the temporary designation of one of Jupiter’s moons. As far as we currently know, this is the smallest moon in the Solar System.
Significance of Designation
S/2003 J 12 is the temporary designation of a small satellite of Jupiter. If its existence is confirmed and satisfactory orbital data become available, it will be given a permanent name. However, sometimes these satellites with temporary designations disappear or prove to be inaccurate observations.
The cryptic temporary designation is not hard to decipher. In case we missed the point, the NASA website explains it. The “S” indicates that the object is a satellite. The “2003” indicates that the object was discovered in 2003. The “J” associates the object with Jupiter. Since the “S” has already told us that the object is a satellite, we now know that the object is a satellite of Jupiter. Finally, the “12” tells us that 11 other Jovian satellites were discovered in 2003 before the one which we are studying.
Scott Shepherd and his team made the discovery. They used a powerful telescope on Mauna Kea in Hawaii.
According to figures given by NASA and other sources, the diameter of S/2003 J 12 is only one kilometer. Wikipedia calls it “the smallest known satellite in the Solar System.” This is correct if we ignore the fact that the tiny particles in planetary rings are actually tiny satellites of the planet about which they revolve. Moreover, we must remember that there is a lot of guesswork involved when these small satellites are measured from a great distance.
According to NASA, the density of this satellite is 2.6 grams per cubic centimeter. This, of course, is an estimate.
S/2003 J 12 has a retrograde orbit. This means that it revolves around Jupiter in a clockwise direction, assuming that our clock is perched above the North Pole of Jupiter. Or to put it another way, if it were possible to observe it from the Jupiter, it would travel westward across the celestial sphere.
In this respect, our midget moon differs from all the Jovian moons with orbits closer to Jupiter, at least as far as we know at present. Jupiter’s four inner satellites have prograde orbits. The same is true of the four Galilean moons, Themisto, the four moons of the Himalia group, and Carpo.
According to NASA, the semimajor axis of S/2003 J 12 is 17,835,000 km. The semimajor axis is roughly the average distance of the orbit from the center of the mother planet. However, the orbit is extremely eccentric, so the distance of the satellite from the mother planet varies considerably.
According to NASA, the inclination of its orbit is 150.827 degrees. If you view the angle in another way, it is only 29.173 degrees. The reason why astronomers choose the larger figure is because of the satellite’s retrograde motion.
The nearest known neighbors of our little midget are Carpo and Euporie. The orbit of Carpo is closer to Jupiter than S/2003 J 12, and the orbit of Euporie is farther away.
NASA: S/2003 J 12
Wikipedia: S/2003 J 12