A dozen new moons of Jupiter – including a maverick

With 67 moons, Jupiter was already the record holder among all the planets of the Solar System. Now a team of astronomers has identified twelve more moons of Jupiter for a grand total of 79. The researchers first discovered the new moons in 2017 while searching for objects at the outermost edge of the Solar System. “Jupiter just happened to be in the way,” explained team leader Scott S. Sheppard of the Carnegie Institution for Science. Confirmation that the new objects actually had an orbit around Jupiter took one year.

Nine of the new moons form a small group that orbit Jupiter in the direction opposite Jupiter’s rotation, i.e., they have retrograde orbits, with a period of two Earth years. It is conjectured that they are the fragments of three larger objects that were destroyed in collisions.

Two of the new moons are part of an inner group with prograde orbits. These are also conjectured to have once been part of a larger moon. Their orbital period is less than one Earth year.

The twelfth moon has some peculiar characteristics. It orbits Jupiter on a prograde path that intersects the orbits of the retrograde moons. Thus, it keeps entering oncoming traffic again and again. “A highly unstable orbit,” the researchers say, which will lead at some point to more collisions. They believe that the maverick is the remnant of a moon, from which the other retrograde moons were produced by earlier impacts. The maverick moon now measures only approximately one kilometer, and is proposed to be named “Valetudo,” after Jupiter’s great-granddaughter, the goddess of health and hygiene.

Valetudo on pictures from the Magellan Telescopes. The moon can be identified by the motion relative to the background stars (Picture: Carnegie Institution for Science)
Diagram of the newly discovered moons. Valetudo is shown in green (Picture: Roberto Molar-Candanosa / Carnegie Institution for Science)

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