Chapter 1: The Cosmic Competition

The rapid pace of astronomical discoveries suggests that textbooks will need continual updates for years to come. With advancements in technology, our ability to explore deeper into the cosmos is accelerating. Reflecting on my school days, I recall Jupiter boasting 13 moons, while Saturn had 9. Fast forward to today, and Jupiter's moon count has soared to 92, with Saturn closely trailing at 83.

In 2019, I reported that Saturn had claimed the 'Moon King' title after discovering 20 new moons, surpassing Jupiter's 79 at that time. However, the Minor Planet Center (MPC) has now announced the orbits of 12 previously unreported moons of Jupiter, bringing its total well ahead of Saturn's 83 confirmed moons.

This ongoing rivalry between these two gas giants for lunar dominance is far from settled. Recent searches for celestial objects at least 3 kilometers in size orbiting these planets have shown that Saturn possesses three times more such objects than Jupiter. This abundance may have resulted from a collision that fragmented a larger moon millions of years ago.

While these fragments have yet to be officially recognized as moons, their inclusion could potentially elevate Saturn's moon count. For now, let’s focus on the intriguing new discoveries. All twelve newly identified moons of Jupiter orbit at considerable distances, each taking over 340 days to complete an orbit. Nine of them are part of the 71 Jovian moons that have the most distant orbits, taking more than 550 days to circle the planet.

The newly discovered moons are likely captured bodies, exhibiting retrograde orbits that move in the opposite direction to the inner moons. Among the retrograde moons, only five exceed 8 kilometers in diameter, while the remaining are believed to have originated from larger objects that were shattered during collisions. Three of the new moons belong to a group of 13 with prograde orbits, positioned between the substantial Galilean moons and the distant retrograde moons.

These prograde moons are believed to have formed where they currently reside, but they are more challenging to detect due to their proximity to Jupiter and the intense light scattered by the planet. Prior to 2000, only five of these moons were identified, with an additional eight discovered since then.

The groupings of these Jovian moons are depicted above. The prograde moons beyond the Galilean moons can be classified into two groups: the nine moons of the Himalia group, which orbit between 11 and 12 million kilometers from Jupiter, and the more distant Carpo group, consisting of just two moons that orbit at a distance of 17 million kilometers from Jupiter. Recent findings have added two moons to the Himalia group and one to the Carpo group.

In comparison to asteroids and comets, which can often be identified after only a few weeks of observation, confirming the existence of lunar bodies involves a more intricate process. This includes extensive observations and complex trajectory calculations. Observations must track a moon over a complete orbit to confirm it genuinely orbits the planet; in this case, Jupiter's outer moons take about two years to complete their orbits.

Complete research findings were published in The Planetary Science Journal.

Saturn Reclaims 'Moon-King' Title: Discoveries Unveiled

Astronomers recently identified 62 new satellites orbiting Saturn, reigniting the competition for the title of 'Moon King.'

Jupiter Overtakes Saturn: The Battle of Moons Continues

Jupiter's newfound status as the planet with the most moons highlights the dynamic nature of celestial discoveries and ongoing research.