Himalia group

The Himalia group is a group of prograde non-spherical moons of Jupiter that follow similar orbits to Himalia and are thought to have a common origin.

This diagram compares the orbital elements and relative sizes of the members of the Himilia group. The horizontal axis illustrates their average distance from Jupiter, the vertical axis their orbital inclination, and the circles their relative sizes.

This diagram illustrates all the irregular satellites of Jupiter. The Himalia group is bunched together near the top of the diagram. An object's position on the horizontal axis indicates its distance from Jupiter. The vertical axis indicates its inclination. Eccentricity is indicated by yellow bars illustrating the object's maximum and minimum distances from Jupiter. Circles illustrate an object's size in comparison to the others.

The known members of the group are (in order from closest to farthest from Jupiter):

• Leda
• Himalia (the biggest, which gives its name to the group)
• Lysithea
• Elara

The orbit estimate of the recently found moon S/2000 J 11 also qualified it as a member of the group (it appeared to have the same inclination, and a slightly bigger semi-major axis) but its orbit is not known exactly and the mean orbital elements have not yet been calculated.

The International Astronomical Union (IAU) reserves names in -a for the moons in this group.

Characteristics and origin

The objects in the Himalia group have semi-major axes (distances from Jupiter) in the range of 11,150,000 and 11,750,000 km, inclinations between 26.6° and 28.3°, and eccentricities of between 0.11 and 0.25. All moons in the group are grey similar to C-type asteroids. It has been suggested that the group could be a remnant of the break-up of an asteroid from the main asteroid belt. The radius of the parent asteroid was probably about 89 km, only a bit bigger than that of Himalia, which retains approximately 87% of the mass of the original body. This indicates the asteroid was not heavily disturbed.