TWELVE NEW MOONS FOR JUPITER

This is an ongoing race between Jupiter and Saturn for the title of planet surrounded by several moons. Until a few days ago Saturn was in the lead with 83 moons confirmed compared to 80 from Jupiter. The Minor Planet Center has now confirmed the presence of twelve other satellites around Jupiter, bringing the total to 92, thus surpassing Saturn!

All the new twelve moons are small and located on very outer orbits, with a period of revolution exceeding 340 days.

Nine of the twelve moons are located on a retrograde orbit with a period of more than 550 days. Retrograde orbit suggests that these moons did not form around Jupiter, but that they are asteroids captured by its gravitational pull.

The three remaining moons move instead on more internal prograde orbits. These appear to have formed in orbit around the gas giant.

Of these twelve objects only five have a diameter of more than 8 km, while the size of the remaining are between 1 and 3 km.

Confirming the presence of satellites in orbit to the gas giants is not an easy job and requires years of work. The orbit of the satellites is influenced by both the gravitational force of the planet and that of the Sun. 

The discovery of a potential moon must therefore keep it constantly under surveillance throughout its orbit to ensure that it is truly in stable orbit around the planet. Since Jupiter’s outermost moons take up to two years to complete a revolution, this implies at least two years of almost continuous observations over time.

The advent of new-generation telescopes and the development of sensors for the study of gaseous giants will increase the number of moons known around Jupiter and Saturn. Numerical simulations, for example, suggest that there are more moons around Saturn than for all the other planets in the Solar System added together. Of these, only some tens have been observed directly so far. 

Credit: NASA, ESA, Hubble, OPAL Program, STScI, Karol Masztalerz.