Himalia group
Overview
The Himalia group is a collection of Jupiter's moons that share similar orbits, colors, and spectral features, indicating a common origin. They are thought to be remnants of a captured asteroid or minor planet that was subsequently fragmented by collisions. The group is named after its largest member, Himalia, which is also the fifth largest of Jupiter's moons.
Discovery and Naming
The first member of the Himalia group, Himalia itself, was discovered by Charles Dillon Perrine at the Lick Observatory on December 3, 1904. It was the first Jovian moon discovered since Galileo Galilei's discovery of the four largest moons in 1610. The remaining members of the group were discovered much later, with the most recent discovery, Ersa, being made in 2018.
The moons in the Himalia group are named after daughters of Zeus, the Greek equivalent of the Roman god Jupiter. The exception is Himalia, who was a nymph loved by Zeus.
Physical Characteristics
The Himalia group's members range in size from about 4 to 170 kilometers in diameter. They are irregularly shaped, indicating that they are likely remnants of a larger body that was fragmented by impacts. The moons have a reddish color, similar to C-type asteroids, suggesting a carbonaceous composition.
Orbital Characteristics
The moons in the Himalia group have similar orbits, which are prograde, meaning they orbit in the same direction as Jupiter's rotation. Their orbits are also inclined to Jupiter's equator, which is unusual for the planet's moons. These characteristics suggest that the moons are captured asteroids or minor planets.
Members
The Himalia group consists of five moons: Himalia, Leda, Lysithea, Elara, and Ersa. Himalia is the largest, with a diameter of about 170 kilometers. The smallest, Ersa, has a diameter of about 4 kilometers.
Formation and Evolution
The Himalia group is thought to have formed from a captured asteroid or minor planet that was subsequently fragmented by collisions. This theory is supported by the moons' similar orbits and spectral characteristics, as well as their irregular shapes.
Exploration
The Himalia group has not been the target of any dedicated space missions. However, several spacecraft have observed the moons during flybys of Jupiter. The most detailed observations have been made by the Galileo and Juno spacecraft.