Jupiter is the most massive planet in our solar system, and it also has a long cohort of other moons. To date, 79 are known, of which twenty-three remain without an official name; those who have received it are named after lovers or daughters of the Roman god Jupiter or his Greek equivalent, Zeus. To these must be added the numerous minor irregular-looking moons whose origin is in asteroids or pieces of asteroids that were trapped in Jupiter’s gravitational well. Together they are not something relevant in the Jovian system, since all of them only account for 0.003% of the total mass that is in orbit around the gas giant.
Astronomers organize the Jupiter satellite system into three groups. From farther to closer to the planet, we have the group of irregular satellites – bodies trapped by Jupiter’s gravity -; the moons of Galileo; and the group of inner moons Metis, Adrastea, Amalthea and Thebe, small rocky bodies of which little is known and that were discovered by the Voyager 1 probe in 1979. These four are within the orbit of Io and take less than one day to revolve around Jupiter following more or less regular orbits. The largest of all, Amalthea (about 160 km in diameter), it seems that it did not form there, but was either captured by Jupiter or cooked at greater distances and ended up falling where it is now. Its orbit around Jupiter is twelve hours.
These moons, along with an unknown number of smaller ones, are the ones that keep the weak ring system that surrounds the gas giant stable: while Metis and Adrastea take care of the main ring, Amalthea and Thebe do the same with the rings. exteriors.
The discovery of this peculiar ring system was one of the great surprises of the Voyager missions. It extends 53,000 km into the planet’s atmosphere, and when viewed head-on it captures less than 0.1% of the light that passes through it, making it virtually transparent: Pioneer 11 traversed that ring in 1974 without realizing its existence. Apparently, the particles that make it up are only visible when viewed in profile or against the Sun.
In the group of the outermost satellites, whose representatives are Sinope, Pasifae, Carmé, Himalia, Temisto and Ananké (which are accompanied by a whole panoply of smaller ones), none exceed 50 km in diameter. Without exception, they are located beyond the orbit of Callisto and, on average, take two years to make a complete revolution of the planet following very eccentric orbits, which confirms their extrajovian origin.
