Himalia group
Image:TheIrregulars JUPITER Himalia.svg|thumb|right|300px|This diagram compares the orbital elements and relative sizes of the largest four members of the Himalia group. The horizontal axis illustrates their average distance from Jupiter, the vertical axis their orbital inclination, and the circles their relative sizes.
[Image:TheIrregulars JUPITER GROUPS.svg|thumb|right|300px|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 Himalia group is a group of prograde irregular satellites of Jupiter that follow similar orbits to Himalia and are thought to have a common origin.
Two additional possible satellites discovered by Sheppard in 2017 were identified to be likely part of the Himalia group, but were too faint to be tracked and confirmed as satellites. They were later officially announced in 2023.
The International Astronomical Union reserves names for moons of Jupiter ending in -a for the moons in this group to indicate prograde motions of these bodies relative to Jupiter, their gravitationally central object.
Characteristics and origin
The objects in the Himalia group have semi-major axes in the range of 11.10 and 12.30 Gm, inclinations between 27.2° and 29.1°, and eccentricities between 0.11 and 0.24. All orbit in a prograde direction. In physical appearance, the group is very homogeneous, all satellites displaying neutral colours similar to those of C-type asteroids. Given the evident clustering of the orbital parameters and the spectral homogeneity, it has been suggested that the group could be a remnant of the break-up of an asteroid from the main asteroid belt, possibly from the Hilda group or the Nysa family. The radius of the parent asteroid was probably about 89 km, only slightly larger than that of Himalia, which retains approximately 87% of the mass of the original body. This indicates the asteroid was not heavily disturbed.Numerical integrations show a high probability of collisions among the members of the prograde group during the lifespan of the Solar System. In addition, the same simulations have shown fairly high probabilities of collisions between prograde and retrograde satellites. Consequently, it has been suggested that the current group could be a result of a more recent, rich collisional history among the prograde and retrograde satellites as opposed to the single break-up shortly after the planet formation that has been inferred for the Carme and Ananke groups. Many of the smaller members of the group that once existed are predicted to have been removed in collisions with Himalia itself over the past 4 billion years.
However, the members of the Himalia group are relatively widely dispersed in their orbital elements, more so than can be conventionally explained with a collisional origin. There are multiple theories proposed to explain this. Gravitational interactions such as secular resonances between Himalia and the other moons over time could be a factor, but while it is the most dominant of all potential perturbation sources, it is not enough by itself to explain all of the scattering. There may have been more than one collision in the group's history that contributed to the dispersion today. Alternatively, the parent asteroid may have been already captured and the collisional family already formed while planetary migration was ongoing, and gravitational interactions between Jupiter and other planet-sized objects may have displaced the moons from their orbits.
List
The known members of the group are :| Name | Diameter | Semi-Major Axis | Period | Notes |
| Himalia | 139.6 | 249.91 | largest member and group prototype | |
| Elara | 79.9 | 258.89 | ||
| Lysithea | 42.2 | 258.50 | ||
| Leda | 21.5 | 240.33 | ||
| Dia | 4 | 277.25 | ||
| Pandia | 3 | 251.23 | ||
| Ersa | 3 | 248.62 | ||
| S/2018 J 2 | 3 | 249.28 | ||
| S/2011 J 3 | 3 | 259.09 |